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Seminal Fluid-mediated Fitness Traits in Drosophila
Abstract
The seminal fluid of male Drosophila contains a cocktail of proteins that have striking effects on male and female fitness. In D. melanogaster, seminal fluid proteins affect female receptivity, ovulation, oogenesis, sperm storage, sperm competition and mating plug formation. In addition, the seminal fluid contains antibacterial peptides and protease inhibitors. Some seminal fluid-encoding genes also show high rates of evolutionary change, exhibiting both significant between-species divergence and within-species polymorphism. Seminal fluid protein genes are expressed only in males, begging the question of how and why the reproductive processes of females are influenced by males. In this review I address these issues by bringing together evidence for the function, evolution, diversification, and maintenance of variation in, seminal fluid-mediated traits.
... During mating, males of many insect species transfer seminal fluid, composed of molecules derived from the accessory glands (MAG), testes, seminal vesicles, ejaculatory bulb and/or ejaculatory duct (figure 1a) [1,2]. The seminal fluid proteins (Sfps) are associated with changes in female post-copulatory behaviour and physiology. ...
... The seminal fluid proteins (Sfps) are associated with changes in female post-copulatory behaviour and physiology. These changes include reducing female mating receptivity, promoting feeding, sperm storage and release and egg production, altering antimicrobial functions, physiology and structure of the female reproductive and digestive tracts, activity level and lifespan [1][2][3]. As a result, these proteins are of interest both for understanding basic reproductive biology and for applications such as development of novel approaches to pest management. ...
... The transfer of immune response-related proteins during the mating process could be important to decrease the probability of sexually transmitted disease infection or to combat infections caused due to injuries during mating [1,49,50]. In A. ludens, the male introduces the basal sac of the distiphallus which has teeth [51] that may damage the female's reproductive apparatus and cause more susceptibility to contract diseases. ...
Seminal fluid proteins (Sfps) modify female phenotypes and have wide-ranging evolutionary implications on fitness in many insects. However, in the Mexican fruit fly, Anastrepha ludens , a highly destructive agricultural pest, the functions of Sfps are still largely unknown. To gain insights into female phenotypes regulated by Sfps, we used nano-liquid chromatography mass spectrometry to conduct a proteomic analysis of the soluble proteins from reproductive organs of A. ludens . The proteins predicted to be transferred from males to females during copulation were 100 proteins from the accessory glands, 69 from the testes and 20 from the ejaculatory bulb, resulting in 141 unique proteins after accounting for redundancies from multiple tissues. These 141 included orthologues to Drosophila melanogaster proteins involved mainly in oogenesis, spermatogenesis, immune response, lifespan and fecundity. In particular, we found one protein associated with female olfactory response to repellent stimuli (Scribble), and two related to memory formation (aPKC and Shibire). Together, these results raise the possibility that A. ludens Sfps could play a role in regulating female olfactory responses and memory formation and could be indicative of novel evolutionary functions in this important agricultural pest.
... In the sperm plug of distinct insect www.nature.com/scientificreports/ species, proteins and lipids have been detected 14,48,49 . For example, in Drosophila protein contributes to forming of the plug 49 , but in the bumblebee B. terrestris the active substances are fatty acids 14,48 . ...
... species, proteins and lipids have been detected 14,48,49 . For example, in Drosophila protein contributes to forming of the plug 49 , but in the bumblebee B. terrestris the active substances are fatty acids 14,48 . The presence of a sperm plug may increase the probability of paternity 32 , and males may benefit by increasing investment in a single female. ...
Reproduction involves high energetic costs which are related to behaviour and gamete production. In females energy allocation to gamete production has been well documented. However, estimations of male investment in seminal material are scarce. The present study aims to assess and compare male investment in four brachyuran species by determining biochemical substrates present in the vasa deferentia to subsequently estimate energetic investment during the reproductive cycle. We identified two groups with contrasting energy investments. Two species, Homalaspis plana and Romaleon setosum, showed high investment due to significant quantities of proteins and lipids. Both species are characterised by large and complex vasa deferentia, and the formation of a remarkably large sperm plug deposited to the female after copulation as a sperm competition avoidance strategy. In contrast, Metacarcinus edwardsii and Taliepus dentatus invested little energy in their smaller-sized and simpler vasa deferentia. Morpho-functional traits may play a key role in determining the investment, which may also be influenced by mechanisms (i.e. mating tactics) to prevent sperm competition and the intensity of polygyny. This study emphasises the high amount of energy males invest in seminal material and highlights the diversity of mating strategies in Brachyura, which are reflected even on the physiological level.
... SFPs are transferred to females along with sperm during mating; their stock in accessory glands eventually becomes depleted after repeated mating (Hihara, 1981;Sirot et al., 2009), and they are costly to produce (both time-and energy-wise). Along other >200 SFPs, they have important effects on post mating processes such as female receptivity (SP), ovulation (SP, Acp26Aa), oogenesis (Acp62F), sperm storage (Acp29AB), and sperm competition (Acp29AB, Acp62F, and Acp36DE) (Avila et al., 2011;Chapman, 2001). Quantifying SFP replenishment allowed us to investigate the impact of infection on male's non-behavioral component of reproductive effort. ...
While mortality is often the primary focus of pathogen virulence, non‐lethal consequences, particularly for male reproductive fitness, are less understood; however, they are essential for understanding how sexual selection contributes to promoting resistance. We investigated how the fungal pathogen Metarhizium brunneum affects mating ability, fertility, and seminal fluid protein (SFP) expression of male Drosophila melanogaster paired with highly receptive virgin females in non‐competitive settings. Depending on sex and dose, there was a 3–6‐day incubation period after infection, followed by an abrupt onset of mortality. Meanwhile, the immune response was strongly induced already 38 h after infection and continued to increase as infection progressed. Latency to mate somewhat increased during the incubation period compared to sham‐treated males, but even on Day 5 post infection >90% of infected males mated within 2 h. During the incubation period, M. brunneum infection reduced male reproductive potential (the number of offspring sired without mate limitation) by 11%, with no clear increase over time. Approaching the end of the incubation period, infected males had lower ability to convert number of mating opportunities into number of offspring. After repeated mating, infected males had lower SFP expression than sham controls, more so in males that mated with few mates 24 h earlier. Overall, despite strong activation of the immune response, males' mating ability and fertility remained surprisingly little affected by the fungal infection, even shortly before the onset of mortality. This suggests that the selection for resistance acts mainly through mortality, and the scope for fertility selection to enhance resistance in non‐competing settings is rather limited.
... This is achieved by transferring seminal fluid proteins (SFPs) and other components to the female during mating. Within mated females, SFPs can induce a range of crucial post-mating responses and functions, such as increasing egg production, stimulating the immune system, and reducing the female's sexual receptivity (Clark et al. 1995;Wolfner 1997Wolfner , 2002Chapman 2001;Haerty et al. 2007;Wolfner 2007, 2009;Findlay et al. 2014;Sirot et al. 2015;Wigby et al. 2020). These SFPs are often rapidly evolving and undergo substantial adaptive changes within a species (Begun et al. 2000;Kern et al. 2004;Begun and Lindfors 2005;Wagstaff and Begun 2005;Findlay et al. 2008Findlay et al. , 2009). ...
Post-mating responses play a vital role in successful reproduction across diverse species. In fruit flies, sex peptide (SP) binds to the sex peptide receptor (SPR), triggering a series of post-mating responses. However, the origin of SPR predates the emergence of SP. The evolutionary origins of the interactions between SP and SPR and the mechanisms by which they interact remain enigmatic. In this study, we used ancestral sequence reconstruction, AlphaFold2 predictions, and molecular dynamics simulations to study SP-SPR interactions and their origination. Using AlphaFold2 and long-time molecular dynamics (MD) simulations, we predicted the structure and dynamics of SP-SPR interactions. We show that SP potentially binds to the ancestral states of Diptera SPR. Notably, we found that only a few amino acid changes in SPR are sufficient for the formation of SP-SPR interactions. Ancestral sequence reconstruction and MD simulations further reveal that SPR interacts with SP through residues that are mostly involved in the interaction interface of an ancestral ligand, myoinhibitory peptides (MIPs). We propose a potential mechanism whereby SP-SPR interactions arise from the pre-existing MIP-SPR interface as well as early chance events both inside and outside the pre-existing interface that created novel SP-specific SP-SPR interactions. Our findings provide new insights into the origin and evolution of SP-SPR interactions and their relationship with MIP-SPR interactions.
... Courtship feeding is prevalent across taxa [16][17][18] , and in extreme cases, mating induces some female insects to feed on male body parts 19,20 . Drosophila exempli es another form of courtship feeding referred to as seminal feeding, whereby males transfer nutrient-rich seminal uids to their mates 21,22 . In general, courtship feeding promotes male paternity because females typically prefer gift-giving males. ...
Seminal fluid is rich in sugars, but their role beyond supporting sperm motility is unknown. In this study, we found Drosophila melanogaster males transfer a substantial amount of a phospho-galactoside to females during mating, but only half as much when undernourished. This seminal substance, which we named venerose, induces an increase in germline stem cells (GSCs) and promotes sperm storage in females, especially undernourished ones. Venerose enters the hemolymph and directly activates nutrient-sensing Dh44⁺ neurons in the brain. Food deprivation directs the nutrient-sensing neurons to secrete more of the neuropeptide Dh44 in response to infused venerose. The secreted Dh44 then enhances the local niche signal, stimulating GSC proliferation. It also extends the retention of ejaculate by females, resulting in greater venerose absorption and increased sperm storage. In this study, we uncovered the role of a sugar-like seminal substance produced by males that coordinates reproductive responses to nutritional challenges in females.
... Different secretory cell types were identified in the glands of the carabid P. nigrita (Krüger et al., 2014). The secretions from the secretory tissues of the male reproductive organs, mainly the accessory glands, are involved in seminal fluid composition (Chapman, 2001). This fluid in insects includes peptides, sugars, fatty acids, and terpenoids, which affect male and female fitness [reviewed by Poiani (2006)]. ...
We investigated the male and female reproductive tracts of Gyretes sp. with light and transmission electron microscopies. The male has a pair of testes with a single coiled follicle, followed by short efferent ducts, which have a similar shape and diameter to the testes. Long ducts (epididymides) with differential epithelium open in a pair of long vasa deferentia that lead to the accessory glands. Glycoprotein secretions from the vas deferens epithelium constitute the spermatostyle for spermatozoa aggregation. The female has numerous ovarioles per ovary, a coiled fertilization duct, an accessory gland, and an elongated vagina. Spermatozoa are stored as unaggregated cells in the fertilization duct. In Gyrinidae, the testes and accessory glands show diverse shapes, and the female sperm storage organs vary in shape, size, and type and may play a role in the interaction with sperm aggregates. Testes with a single follicle and vasa deferentia opening in the accessory glands of Gyretes sp. are features shared with other Gyrinidae and other Adephaga. We proposed adding this latter trait to characterize this suborder of beetles. The morphology of the reproductive organs in both sexes contributes to comparative analyses and knowledge of the reproductive biology of Gyretes and may provide additional features for systematics.
... Different secretory cell types were identified in the glands of the carabid P. nigrita (Krüger et al., 2014). The secretions from the secretory tissues of the male reproductive organs, mainly the accessory glands, are involved in seminal fluid composition (Chapman, 2001). This fluid in insects includes peptides, sugars, fatty acids, and terpenoids, which affect male and female fitness [reviewed by Poiani (2006)]. ...
We investigated the male and female reproductive tracts of Gyretes sp. with light and transmission electron microscopies. The male has a pair of testes with a single coiled follicle, followed by short efferent ducts, which have a similar shape and diameter to the testes. Long ducts (epididymides) with differential epithelium open in a pair of long vasa deferentia that lead to the accessory glands. Glycoprotein secretions from the vas deferens epithelium constitute the spermatostyle for spermatozoa aggregation. The female has numerous ovarioles per ovary, a coiled fertilization duct, an accessory gland, and an elongated vagina. Spermatozoa are stored as unaggregated cells in the fertilization duct. In Gyrinidae, the testes and accessory glands show diverse shapes, and the female sperm storage organs vary in shape, size, and type and may play a role in the interaction with sperm aggregates. Testes with a single follicle and vasa deferentia opening in the accessory glands of Gyretes sp. are features shared with other Gyrinidae and other Adephaga. We proposed adding this latter trait to characterize this suborder of beetles. The morphology of the reproductive organs in both sexes contributes to comparative analyses and knowledge of the reproductive biology of Gyretes and may provide additional features for systematics.
... Within mated females, SFPs can induce a range of crucial post-mating responses and functions, such as increasing egg production, stimulating the immune system, and reducing the female's sexual receptivity (Chapman, 2001; Clark et al. ...
Post-mating responses play a vital role in successful reproduction across diverse species. In fruit flies, sex peptide (SP) binds to sex peptide receptor (SPR), triggering a series of post-mating responses. However, the origin of SPR predates the emergence of SP. The evolutionary origins of the interactions between SP and SPR and the mechanisms by which they interact remain enigmatic. In this study, we used ancestral sequence reconstruction, AlphaFold2 predictions, and molecular dynamics simulations to study SP-SPR interactions and their origination. Using AlphaFold2 and long-time molecular dynamics (MD) simulations, we demonstrate the structure and dynamics of SP-SPR interactions. We show that SP potentially binds to the ancestral states of Diptera SPR. Notably, we found that only a few amino acid changes in SPR are sufficient for the formation of SP-SPR interactions. Ancestral sequence reconstruction and MD simulations further reveal that SP-SPR interacts through residues that are mostly located at the SPR interface of an ancestral ligand, myoinhibitory peptides (MIPs). We propose a potential mechanism whereby SP-SPR interactions arise from pre-existing MIP-SPR interface as well as early chance events that created novel SP-specific SP-SPR interactions. Our findings provide new insights into the origin and evolution of SP-SPR interactions and their relationship with MIP-SPR interactions.
... It is important to note that fecundity encompasses not only the reproductive capacity of females but also factors related to male reproductive function (e.g. Pitnick, 1991;Lefranc & Bundgaard, 2000;Chapman, 2001). Male reproductive traits can ultimately affect reproductive output. ...
In ectotherms, body temperature is a crucial determinant of performance and fitness, as captured by thermal performance curves (TPCs). Since survival in variable environments is often facilitated by phenotypic plasticity, to reliably assess an organism’s ability to cope with thermal changes, it is necessary to characterize not only TPCs but also their reaction norms. While previous studies have investigated plasticity in TPCs, these studies focus only on selected parameters and a few developmental temperatures. They may, therefore, overlook the complexity of developmental plasticity in TPCs. Here, we examined the full extent of thermal developmental plasticity in TPCs for fecundity and hatchability in Drosophila melanogaster. By employing a factorial design with ten developmental and twelve adult temperatures, our study enabled a comprehensive characterization of reaction norms of all key TPC parameters. We found that developmental temperature had a significant impact on the egg production rate, with minor effects on other TPC parameters. Non-optimal developmental temperatures negatively affected most TPC parameters, whereas development at 22-26°C maximized reproductive fitness. We also revealed that developmental plasticity for the maximum reproductive performance might be predominantly caused by developmentally-induced changes in ovariole number. Our results in conjunction with previous studies on intraspecific variation suggest that any changes in TPC for reproduction primarily involve the egg production rate, indicating that adaptive evolution and phenotypic plasticity followed the same pathway. Overall, our findings underscore the limitations of developmental plasticity in enhancing reproductive fitness, suggesting that while certain traits, such as egg production rate, may be relatively plastic, these changes may not be sufficient to enable effective adjustment to environmental shifts.
... The direct fitness consequences of variation in the ejaculate protein composition remain to be explored, particularly considering the potential buffering effect of functional redundancies. Many individual SFPs are known to elicit differential reproductive output [91], but tracking the fitness consequences of condition-dependent abundances in single SFPs does not necessarily exclude the possibility that non-focal proteins may also be affected and contribute to eliciting the phenotypic response. Indeed, in a promiscuous species like D. melanogaster, the reproductive outcome may depend on the interactions between many actors [12], and the effect of individual, differentially abundant ejaculate proteins may be limited depending on their position in the regulatory or functional network. ...
Ejaculate proteins are key mediators of post-mating sexual selection and sexual conflict, as they can influence both male fertilization success and female reproductive physiology. However, the extent and sources of genetic variation and condition dependence of the ejaculate proteome are largely unknown. Such knowledge could reveal the targets and mechanisms of post-mating selection and inform about the relative costs and allocation of different ejaculate components, each with its own potential fitness consequences. Here, we used liquid chromatography coupled with tandem mass spectrometry to characterize the whole-ejaculate protein composition across 12 isogenic lines of Drosophila melanogaster that were reared on a high- or low-quality diet. We discovered new proteins in the transferred ejaculate and inferred their origin in the male reproductive system. We further found that the ejaculate composition was mainly determined by genotype identity and genotype-specific responses to larval diet, with no clear overall diet effect. Nutrient restriction increased proteolytic protein activity and shifted the balance between reproductive function and RNA metabolism. Our results open new avenues for exploring the intricate role of genotypes and their environment in shaping ejaculate composition, or for studying the functional dynamics and evolutionary potential of the ejaculate in its multivariate complexity.
... Males also employ chemical mate guarding strategies to prevent additional matings, marking females with unattractive pheromones postmating, to reduce their chances of remating (Ejima et al., 2007). Experimental evidence suggests that proteins in seminal fluid decrease the tendency of female remating and elevate sperm displacement (Chapman, 2001;Mane et al., 1983;Zawistowski & Richmond, 1986). ...
Bateman's principles, originally a test of Darwin's theoretical ideas, has since become fundamental to sexual selection theory and vital to contextualising the role of anisogamy in sex differences of precopulatory sexual selection. Despite this, Bateman's principles have received substantial criticism, and researchers have highlighted both statistical and methodological errors, suggesting that Bateman's original experiment contains too much sampling bias for there to be any evidence of sexual selection. This study uses Bateman's original method as a template, accounting for two fundamental flaws in his original experiments, (i) viability effects and (ii) a lack of mating behaviour observation. Experimental populations of Drosophila melanogaster consisted of wild-type focal individuals and non-focal individuals established by backcrossing the brown eye (bw -) eye-colour marker - thereby avoiding viability effects. Mating assays included direct observation of mating behaviour and total number of offspring, to obtain measures of mating success, reproductive success, and standardised variance measures based on Bateman's principles. The results provide observational support for Bateman's principles, particularly that (i) males had significantly more variation in number of mates compared to females and (ii) males had significantly more individual variation in total number of offspring. We also find significantly steeper Bateman gradient for males compared to females, suggesting that sexual selection is operating more intensely in males. However, female remating was limited, providing the opportunity for future study to further explore female reproductive success in correlation with higher levels of remating.
... ; https://doi.org/10.1101/2023.08.09.552689 doi: bioRxiv preprint 5 interacts with the male ejaculate to affect female fertilization success. Sexual selection on male 101 reproductive proteins has been inferred through molecular evolution analyses (Begun et al., 102 2000;Swanson & Vacquier, 2002;Clark et al., 2006;Chapman, 2011). These studies indicate 103 that many seminal fluid proteins evolve rapidly due to sexually antagonistic coevolution, which 104 in turn implies that direct selection is acting on both female and male post-insemination traits. ...
Sex-specific regulation of gene expression is the most plausible way for generating sexually differentiated phenotypes from an essentially shared genome. However, since genetic material is shared, sex-specific selection in one sex can have an indirect response in the other sex. From a gene expression perspective, this tethered response can move one sex away from their wildtype expression state and impact potentially many gene regulatory networks. Here, using experimental evolution in the model nematode Caenorhabditis elegans , we explore the coupling of direct sexual selection on males with the transcriptomic response in females over microevolutionary timescales to uncover the extent to which post-insemination reproductive traits share a genetic basis between the sexes. We find that differential gene expression is driven by female ancestral or evolved generation alone and that male generation has no impact on changes in gene expression. Almost all differentially expressed genes were downregulated in evolved females. Moreover, 80% of these gene were located on the X chromosome and have wildtype female-biased expression profiles. Changes in gene expression profiles were likely driven through trans -acting pathways that are shared between the sexes. We found no evidence that the core dosage compensation machinery was impacted by experimental evolution. Together these data suggest masculinization of the female transcriptome driven by direct selection on male sperm competitive ability. Our results indicate that on short evolutionary timescales sexual selection can generate sexual conflict in expression space.
LAY SUMMARY
Sexual selection drives the evolution of some of the most dramatic phenotypic differences between the sexes. Such sexual dimorphism is so common across multicellular organisms that we often overlook how remarkable it is for shared genetic material to create numerous and complex sex differences. At an evolutionary level, sexual dimorphism furthers the opportunity for sex-specific selection to optimize the fitness of a given sex. As a consequence, sex-specific selection, such as sexual selection, can have an indirect evolutionary response in the other sex due to genetic associations created by the sexes sharing the same genome. This correlated evolutionary response can create sexual conflict by shifting a sex away from their fitness optimum. At the functional level, sexual dimorphism is generated is through sex-specific regulation of gene expression. Bridging the evolutionary response to sexual selection with the evolution of sex-specific gene regulation during post-mating interactions has proved challenging. We previously used experimental evolution to increase male fertility by directly selecting for increased sperm competitive ability. In this study, we examined the effect of this direct selection on males on gene expression patterns in females. Differential gene expression was determined by whether a female was ancestral or evolved generation, indicating that gene expression changes were an evolved response due to indirect selection on females. Significantly differentially expressed genes were downregulated in evolved females. These genes tended to be female-biased in wildtype individuals and located on the X chromosome. The downregulation of X-linked genes suggests expression levels in females equal to or lower than that in males. Together these results indicate a less female-like transcriptome after experimental evolution. This supports a sexual conflict scenario by which direct sexual selection on males indirectly masculinizes the female transcriptome over short evolutionary timescales.
... Seminal fluid (SF) in most species is made in specialized accessory reproductive cells, tissues, or glands, such as the prostate, seminal vesicle, bulbourethral, and ampullary glands in humans (McGraw et al., 2015). SFPs have been shown to be especially crucial in male and female reproduction; they belong to a range of molecular classes such as antioxidants, lipases, lectins, proteases, and protease inhibitors and have been shown to have a diverse set of functions (Chapman, 2001;Avila et al., 2011;Perry et al., 2013;Ramm, 2020). For instance, SFPs facilitate normal sperm function (Wolfner, 1997), aid sperm storage and male sperm competitiveness (Fiumera et al., 2005(Fiumera et al., , 2007Goenaga et al., 2015;Patlar et al., 2020), maintain sperm viability (den Boer et al., 2008Boer et al., , 2009King et al., 2011) and regulate sperm capacitation (Manjunath and Thérien, 2002). ...
Reproductive ageing can occur due to the deterioration of both the soma and germline. In males, it has mostly been studied with respect to age-related changes in sperm. However, the somatic component of the ejaculate, seminal fluid, is also essential for maintaining reproductive function. Whilst we know that seminal fluid proteins (SFPs) are required for male reproductive success across diverse taxa, age-related changes in SFP quantity and composition are little understood. Additionally, only few studies have explored the reproductive ageing of the tissues that produce SFPs, and the resulting reproductive outcomes. Here we provide a systematic review of studies addressing how advancing male age affects the production and properties of seminal fluid, in particular SFPs and oxidative stress, highlighting many open questions and generating new hypotheses for further research. We additionally discuss how declines in function of different components of seminal fluid, such as SFPs and antioxidants, could contribute to age-related loss of reproductive ability. Overall, we find evidence that ageing results in increased oxidative stress in seminal fluid and a decrease in the abundance of various SFPs. These results suggest that seminal fluid contributes towards important age-related changes influencing male reproduction. Thus, it is essential to study this mostly ignored component of the ejaculate to understand male reproductive ageing, and its consequences for sexual selection and paternal age effects on offspring.
... Post-copulatory male fitness, in turn, is largely driven by sperm competitiveness (mostly sperm-offense, see Fricke et al. , 2010;Simmons and Fitzpatrick, 2012). Additionally, male manipulation of female reproductive behaviour via the transfer of accessory gland proteins within the seminal fluid is known to benefit male post-copulatory fertilisation success (Chenet al. , 1988;Aigaki et al. , 1991;Chapman, 2001;Chapmanet al. , 2003;Liu and Kubli, 2003;Fiumera, Dumont and Clark, 2005;Ravi Ram and Wolfner, 2007;Fricke et al. , 2009;Hopkinset al. , 2019). In fact, there is ample evidence that males strategically adjust their seminal fluid protein transfer depending on the socio-sexual environment context they experience (see for instance Wigby et al. , 2009;Hopkins et al. , 2019). ...
Phenotypic plasticity in reproductive behaviour can be a strong driver of individual fitness. For example, in species with high intra-sexual competition, changes in socio-sexual context can trigger quick adaptive plastic responses in males. In particular, a recent study in the vinegar fly ( Drosophila melanogaster ) shows that males respond adaptively to perception of female cues in a way that increases their reproductive success, but we ignore the underlying mechanisms of this phenomenon. Here, we aimed to fill this gap by investigating the short-term effects of female perception on male pre- and post-copulatory components of reproductive success: a) mating success, b) mating latency and duration, c) sperm competitiveness, and d) ejaculate effects on female receptivity and oviposition rate. We found that brief sexual perception increased mating duration, but had no effect on the main pre- or post-copulatory fitness proxies. These results tie up with previous findings to suggest that male adaptive responses to sexual perception are not due to a short-term advantage, but rather to fitness benefits that play out across the entire male lifespan.
... These substances could be incorporated directly into eggs or modulate the female physiology in a way that will affect the development of the offspring (e.g., via nutrient allocation). These malederived proteins are known to trigger an impressive range of physiological and behavioral responses by the female (Chapman 2001;Avila et al. 2011) , including support of sperm functioning inside the female reproductive tract, even though the latter could be to ensure fertilization (Sepil et al. 2019). ...
Nongenetic parental effects can contribute to the adaptation of species to changing environments by circumventing some of the limitations of genetic inheritance. A clearer understanding of the influence of nongenetic inheritance and its potentially sex-specific responses in daughters and sons is needed to better predict the evolutionary trajectories of species. However, whereas nongenetic maternal effects have long been recognized and widely studied, comparatively little is known about corresponding paternal effects. Here, by following 30 isogenic lines of Drosophila melanogaster across two generations, each reared under two dietary regimes in each generation, we tested how protein restriction during larval development of the fathers affects the fitness and health of their daughters and sons. We then quantified genetic and non-genetic paternal, and direct environmental, effects across multiple axes of offspring fitness. Daughters and sons responded differently to their father’s developmental history. While isolines differed in mean trait values, their specific responses to protein restriction generally varied little. The sex- and trait-specific responses to paternal effects emphasize the complexity of inter-generational parental effects, which raise important questions about their mode of transmission and adaptive value, including the potential for conflict between the sexes.
... The importance of AGs for male reproductive success in D. melanogaster has been widely studied (Chen, 1984;Wigby et al., 2020;Wolfner, 1997). Seminal fluid proteins (SFPs) secreted mainly by the AGs are transferred together with sperm to the female during mating causing changes in female postmating responses (e.g., behavior and physiology [Chapman, 2001;Chen et al., 1988]). In addition, SFPs affect male sperm competitiveness and modulate sperm storage dynamics inside the female's sperm storage organs (Avila et al., 2011), together ensuring fertility. ...
The predicted temperature increase caused by climate change is a threat to biodiversity. Across animal taxa, male reproduction is often sensitive to elevated temperatures leading to fertility loss, and in more adverse scenarios, this can result in sterility when males reach their upper thermal fertility limit. Here, we investigate temperature‐induced changes in reproductive tissues, fertility reduction, sterility, and the associated fitness loss during the subsequent recovery phase in male Drosophila melanogaster. We heat‐stressed males during development and either allowed them to recover or not in early adulthood while measuring several determinants of male reproductive success. We found significant differences in recovery rate, organ sizes, sperm production, and other key reproductive traits among males from our different temperature treatments. Sperm maturation was impaired before reaching the upper thermal sterility threshold. While some effects were reversible, this did not compensate for the fitness loss due to damage imposed during development. Surprisingly, developmental heat stress was damaging to accessory gland growth, and female post‐mating responses mediated by seminal fluid proteins were impaired regardless of the possibility of recovery. We suggest that sub‐lethal thermal sterility and the subsequent fertility reduction are caused by a combination of inefficient functionality of both the accessory gland and testes. We investigate the consequences of heat stress and the mechanisms of heat‐induced fertility loss and sterility in Drosophila.
... Seminal fluid is transferred to females along with sperm during mating, and its contents are capable of inducing physiological and behavioral changes in female [54,[147][148][149][150][151][152]. For example, the effects of receiving seminal fluid proteins and peptides have been extensively studied in the model organism D. melanogaster and, studies found changes in female remating behaviors (e.g., mating receptivity), ovulation, oogenesis, sperm storage and survival, egg-laying, and a number of other reproductive processes [150,[153][154][155][156][157]. Many of these seminal fluid-mediated post-mating effects on females have also been found in other species [34,132,154,[158][159][160][161][162][163][164][165][166]. ...
The evidence supports the occurrence of environmentally-induced paternal epigenetic inheritance that shapes the offspring phenotype in the absence of direct or indirect paternal care and clearly demonstrates that sperm epigenetics is one of the major actors mediating these paternal effects. However, in most animals, while sperm makes up only a small portion of the seminal fluid, males also have a complex mixture of proteins, peptides, different types of small noncoding RNAs, and cell-free DNA fragments in their ejaculate. These seminal fluid contents (Sfcs) are in close contact with the reproductive cells, tissues, organs, and other molecules of both males and females during reproduction. Moreover, their production and use are adjusted in response to environmental conditions, making them potential markers of environmentally- and developmentally-induced paternal effects on the next generation(s). Although there is some intriguing evidence for Sfc-mediated paternal effects, the underlying molecular mechanisms remain poorly defined. In this review, the current evidence regarding the links between seminal fluid and environmental paternal effects and the potential pathways and mechanisms that seminal fluid may follow in mediating paternal epigenetic inheritance are discussed.
... Seminal fluid is transferred to females along with sperm during mating, and its content is capable of causing physiological and behavioral changes in the females [138][139][140][141][142][143][144]. Notably, the effects of receiving seminal fluid proteins and peptides have been extensively studied in the model organism Drosophila melanogaster including studies that showed changes in female remating latency, receptivity, ovulation, oogenesis, sperm storage and survival, egg-laying rate, and a number of other reproductive functions [142,[145][146][147][148][149]. Many of these seminal fluid-mediated effects in females have been also defined in many other species [34,146,[150][151][152][153][154][155][156][157]. ...
The evidence supports the occurrence of environmentally induced paternal epigenetic inheritance shaping the offspring phenotype in the absence of direct or indirect paternal care, and the empirical results clearly indicate that sperm epigenetics is one of the major actors mediating these paternal effects. However, sperm often make up only a small fraction of the male ejaculate in animals. Males also have a complex mixture of proteins, peptides, types of small RNAs, and cell-free DNA fragments in their seminal fluid. These molecules are in close contact with reproductive cells, tissues, organs, and other molecules of both males and females during reproduction. Moreover, their production and use are very sensitive to environmental conditions which makes them potential modulators of environmentally and developmentally induced paternal effects on the next generation(s). Although there is some intriguing evidence of seminal fluid-mediated paternal epigenetic effects, the underlying molecular mechanisms remain poorly defined. In this review, I discuss the current evidence regarding the association between seminal fluid and environmentally induced paternal effects, the possible trajectories, and the mechanisms in which seminal fluid can involve to mediate paternal epigenetic inheritance.
... As a whole, seminal fluid is critical for male and female fertility -sperm alone is not enough to ensure fertilization -and is implicated in complex behaviors, such as sperm competition, male-female signaling and conflict (Poiani 2006). Most functional work on these seminal fluid proteins comes from the study of dozens of Drosophila accessory gland proteins (Acps) (Chapman 2011). The genes underlying many of these Acps are characterized by their elevated evolutionary rate relative to non-reproductive proteins, indicating adaptive evolution (Begun et al. 2000;Swanson and Vacquier 2002;Clark et al. 2006;Wilburn and Swanson 2016). ...
Nematode sperm contain subcellular vesicles known as membranous organelles (MOs) that fuse with the cell membrane upon sperm activation to release their soluble contents into the extracellular space. The second most abundant proteins in the MOs belong to the conserved Nematode-Specific Peptide family, group F (NSPF) gene family. We hypothesize that these proteins contribute to seminal fluid and are part of post-insemination reproductive tract dynamics. We characterized the anatomical region where the NSPF proteins likely function during fertilization using whole-worm immunostaining of a His-tagged nspf-1 transgene. We confirmed that NSPF proteins are transferred to females during mating. NSPF proteins localize to the uterus lumen when transferred to mated females and in unmated adult hermaphrodites. These results suggest that the uterine localization of the NSPF proteins is likely a functional property of both male-derived sperm and self-sperm and not incidental to the point of transfer during mating. In males, we found that NSPF presence and abundance was correlated with reproductive maturity. We then used experimental evolution to compete the wildtype allele against a deletion allele in 10 replicate obligate-outcrossing populations. We calculated a mean selective disadvantage of 0.1% for the deletion allele, which indicated that the NSPF genes are beneficial to male fitness. This conclusion was reinforced by qualitative trends from lower powered single-generation fertility assays. Together we demonstrate that nematodes use a novel mechanism for generating seminal fluid proteins and show that the highly abundant NSPF proteins likely have a beneficial impact on fitness.
... Additionally, male manipulation of female reproductive behavior via the transfer of accessory gland proteins within the seminal fluid is known to benefit male post-copulatory fertilization success (Aigaki et al., 1991;Chapman, 2001;Chen et al., 1988;Fiumera et al., 2005;Fricke et al., 2009;Hopkins et al., 2019;Liu & Kubli, 2003;Ravi Ram & Wolfner, 2007). In fact, there is firm evidence showing that males strategically adjust the transfer of seminal fluid proteins in response to the socio-sexual context they experience (Hopkins et al., 2019;Sirot et al., 2011;). ...
Phenotypic plasticity in reproductive behavior can be a strong driver of individual fitness. In species with high intra‐sexual competition, changes in socio‐sexual context can trigger quick adaptive plastic responses in males. In particular, a recent study in the vinegar fly (Drosophila melanogaster) shows that males derive net fitness benefits from being shortly exposed to female cues ahead of access to mating (termed sexual perception), but the underlying mechanisms of this phenomenon remain unknown. Here, we investigated the short‐term effects of female perception on male pre‐ and post‐copulatory components of reproductive performance: (a) mating success, (b) mating latency and duration, (c) sperm competitiveness, and (d) ejaculate effects on female receptivity and reproductive rate. We found that brief sexual perception increased mating duration, but had no effect on the other main pre‐ and post‐copulatory fitness proxies recorded. This suggests that perception of female cues may not yield net fitness benefits for males in the short‐term, but we discuss alternative explanations and future avenues of research. A recent study in the vinegar fly (Drosophila melanogaster) shows that males respond adaptively to perception of female cues in a way that increases their reproductive success, but we ignore the underlying mechanisms of this phenomenon. We found that brief sexual perception increased mating duration, but had no effect on the main pre‐ or post‐copulatory fitness proxies. These results tie up with previous findings to suggest that previously documented male adaptive responses to sexual perception may not be due to a short‐term advantage, but rather to fitness benefits that play out across the entire male lifespan.
... The male seminal fluid is a complex medium, that contains many molecules and complex components, such as seminal fluid proteins (SFPs), produced mainly by sex accessory glands (Poiani et al., 2006;Sirot et al., 2014;McGraw et al., 2015). In the mating behavior of insects, SFPs are transferred from males to females through ejaculation, which has possible benefits including sperm capacitation, sperm competition and fertilization, and plays a crucial role in reproductive success (Chapman et al., 2001;Avila et al., 2011;Denis et al., 2017;Taniguchi et al., 2018;Karr et al., 2019). In Drosophila melanogaster, RNAi-mediated knockdown of a type of SFP, Seminase, a predicted serine protease, results in a decrease of eggs and an inability to store sex peptides (LaFlamme et al., 2012). ...
Male fertility is essential for reproduction and population growth in animals. Many factors affect male fertility, such as courtship behavior, sperm quantity, and sperm motility, among others. Seminal Fluid Proteins (SFPs) are vital components of seminal fluid in the male ejaculate, which affect male fertility, sperm activation, and female ovulation. However, the knowledge of SFPs is insufficient; the function of many SFPs remains unknown, and most described functions were mainly characterized in Drosophila or other laboratory models. Here, we focus on the Serine protease 2 (Ser2) gene in the lepidopteran pest Spodoptera litura. The Ser2 gene was specifically expressed in male adults. Disruption of the Ser2 gene mediated by CRISPR/Cas9 induced male sterility but females remained fertile. PCR-based detection of the next-generation mutants showed that male sterility was stably inherited. The qRT-PCR analysis of SlSer2 mutants showed that motor protein family genes and structural protein family genes were down-regulated, while protein modification family genes were up-regulated, suggesting that SlSer2 may be involved in sperm movement and activity. These results demonstrate that Ser2 is an important component of SFPs in seminal fluid and was identified for a useful sterile gene for pest control that may lead to new control strategies for lepidopteran insect pests such as S. litura.
... Sfps of male insects are transferred to females during mating and induce numerous behavioral and physiological post-mating changes in females. These changes include increasing egg production; affecting sperm storage parameters and the extent of post-copulatory sexual selection; decreasing receptivity to remating; and modulating sperm competition, feeding behaviors, and mating plug formation [87][88][89][90]. Therefore, the down-regulated Sfps in the IAD-fed insects could contribute to lower egg viability and reduced fecundity. ...
The development of artificial diets could considerably simplify and reduce the cost of mass rearing of natural enemies compared to conventional rearing methods. However, improvement of artificial diets can be tedious, convoluted and often uncertain. For accelerating diet development, a better method that can offer informative feedback to target deficiencies in diet improvement is required. Our previous research demonstrated several biological characteristics were diminished in the insect predator, Arma chinensis Fallou, fed on an artificial diet formulated with the aid of transcriptomic methods compared to the Chinese oak silk moth pupae. The present study reports differential proteomic analysis by iTRAQ-PRM, which unravels the molecular mechanism of A. chinensis responding to improvements in the artificial diet. Our study provides multivariate proteomic data and provides comprehensive sequence information in studying A. chinensis. Further, the physiological roles of the differentially expressed proteins and pathways enable us to explain several biological differences between natural prey-fed and improved diet-fed A. chinensis, and subsequent proposed reformulation optimizations to artificial diets.
... Among other things, they are known to activate and energise sperm, affect female oviposition rate and receptivity, and influence microbial activity around sperm and eggs (e.g. Chapman, 2001;Chapman et al., 1995;Fitzpatrick & Lüpold, 2014;Giacomello et al., 2008;Poiani, 2006). ...
In species with alternative reproductive tactics, there is much empirical support that parasitically spawning males have larger testes and greater sperm numbers as an evolved response to a higher degree of sperm competition, but support for higher sperm performance (motility, longevity, speed) by such males is inconsistent. We used the sand goby (Pomatoschistus minutus) to test whether sperm performance differed between breeding‐coloured males (small testes, large mucus‐filled sperm‐duct glands; build nests lined with sperm‐containing mucus, provide care) and parasitic sneaker‐morph males (no breeding colouration, large testes, rudimentary sperm‐duct glands; no nest, no care). We compared motility (proportion motile sperm), velocity, longevity of sperm, gene expression of testes, and sperm morphometrics between the two morphs. We also tested if sperm‐duct gland contents affected sperm performance. We found a clear difference in gene expression of testes between the male morphs with 109 transcripts differentially expressed between the morphs. Notably, several mucin genes were upregulated in breeding‐coloured males and two ATP‐related genes were upregulated in sneaker‐morph males. There was a partial evidence of higher sperm velocity in sneaker‐morph males, but no difference in sperm motility. Presence of sperm‐duct gland contents significantly increased sperm velocity, and non‐significantly tended to increase sperm motility, but equally so for the two morphs. The sand goby has remarkably long‐lived sperm, with only small or no decline in motility and velocity over time (5 min vs 22 h), but again, this was equally true for both morphs. Sperm length (head, flagella, total, flagella‐to‐head ratio) did not differ between morphs, and did not correlate with sperm velocity for either morph. Thus, other than a clear difference in testes gene expression, we found only modest differences between the two male morphs, confirming previous findings that increased sperm performance as an adaptation to sperm competition is not a primary target of evolution.
... Copulation duration is another estimate of reproductive effort/investment by males as copulation in D. melanogaster lasts substantially longer than required for sperm transfer alone, with the additional time spent in the transfer of accessory gland proteins (Acps) (Gilchrist and Partridge 2000). Many of these Acps are known to mediate sexually antagonistic effects in females (Chapman et al. 1995;Wolfner 2002;Chapman 2001). We note that we have not directly assessed sexual selection via variation in male reproductive success and that, therefore, our results are suggestive rather than conclusive. ...
The role of sexual selection in mediating levels of sexual conflict has been demonstrated in many experimental evolution studies on Drosophila spp. where competition among males for mating was the target of selection. Sexual selection has also been shown to affect the evolution of life-histories. However, the influence of divergent life-histories on reproductive strategies and, therefore, sexual selection and possibly sexual conflict has been less well studied. We examined D. melanogaster populations selected for a short development time and early age at reproduction for changes in reproductive behavior and traits that are proxies of sexual selection. We report a large reduction in reproductive competition experienced by the males of these populations, compared to ancestral populations that are not consciously selected for rapid development or early reproduction, potentially leading to reduced sexual selection. We show that rapidly developing and early reproducing populations have very low levels of mating in their lifetime (females are more or less monandrous), low courtship levels, shorter copulation duration, and longer time from eclosion to first mating, compared to the controls. These results are discussed in the context of the previously demonstrated reduction of inter-locus sexual conflict in these populations. We show that life-history strategies might have a large and significant impact on sexual selection, with each influencing the other and contributing to the complexities of adaptation.
Significance statement
Sexual conflict, often manifested as an arms-race between males and females trying to enhance their own reproductive success at some cost to the other, is of great evolutionary interest because it can maintain genetic variation in populations, prevent the independent optimization of male and female traits, and also promote speciation. Sexual selection, or variation in mating success, is well known to affect levels of sexual conflict. However, it is not so clear whether, and how, the regular evolution of life-histories also affects sexual selection. Here, we show that life-history evolution in fruit fly populations selected for traits not directly related to sexual conflict might, nevertheless, mediate the possible evolution of altered sexual conflict levels through effects on sexual selection. Populations that evolved to develop to adulthood fast, and reproduce relatively early in life, are shown to potentially experience less sexual selection, which can explain the low sexual conflict levels earlier observed in them.
... Any of several non-exclusive models might explain the evolution of SP's effects on females. Firstly, SP might have arisen for an ancestral function (such as mediating the transfer of other SFPs; see Sections IV.3 and V.2), and females might subsequently have adopted SP as a cue of ejaculate receipt (Manning, 1967;Chapman, 2001;Brockhurst et al., 2014), evolving sensory apparatus that feeds the detection of SP into the induction of reproductive processes. In the language of animal signalling, 'cues' provide information, but they have not been shaped by natural selection to do so; instead, they evolve for other functions (Maynard- Smith & Harper, 2003;Laidre & Johnstone, 2013). ...
A central paradigm in evolutionary biology is that the fundamental divergence in the fitness interests of the sexes (‘sexual conflict’) can lead to both the evolution of sex‐specific traits that reduce fitness for individuals of the opposite sex, and sexually antagonistic coevolution between the sexes. However, clear examples of traits that evolved in this way – where a single trait in one sex demonstrably depresses the fitness of members of the opposite sex, resulting in antagonistic coevolution – are rare. The Drosophila seminal protein ‘sex peptide’ (SP) is perhaps the most widely cited example of a trait that appears to harm females while benefitting males. Transferred in the ejaculate by males during mating, SP triggers profound and wide‐ranging changes in female behaviour and physiology. Early studies reported that the transfer of SP enhances male fitness while depressing female fitness, providing the foundations for the widespread view that SP has evolved to manipulate females for male benefit. Here, we argue that this view is (i) a simplification of a wider body of contradictory empirical research, (ii) narrow with respect to theory describing the origin and maintenance of sexually selected traits, and (iii) hard to reconcile with what we know of the evolutionary history of SP's effects on females. We begin by charting the history of thought regarding SP, both at proximate (its production, function, and mechanism of action) and ultimate (its fitness consequences and evolutionary history) levels, reviewing how studies of SP were central to the development of the field of sexual conflict. We describe a prevailing paradigm for SP's evolution: that SP originated and continues to evolve to manipulate females for male benefit. In contrast to this view, we argue on three grounds that the weight of evidence does not support the view that receipt of SP decreases female fitness: (i) results from studies of SP's impact on female fitness are mixed and more often neutral or positive, with fitness costs emerging only under nutritional extremes; (ii) whether costs from SP are appreciable in wild‐living populations remains untested; and (iii) recently described confounds in genetic manipulations of SP raise the possibility that measures of the costs and benefits of SP have been distorted. Beyond SP's fitness effects, comparative and genetic data are also difficult to square with the idea that females suffer fitness costs from SP. Instead, these data – from functional and evolutionary genetics and the neural circuitry of female responses to SP – suggest an evolutionary history involving the evolution of a dedicated SP‐sensing apparatus in the female reproductive tract that is likely to have evolved because it benefits females, rather than harms them. We end by exploring theory and evidence that SP benefits females by functioning as a signal of male quality or of sperm receipt and storage (or both). The expanded view of the evolution of SP that we outline recognises the context‐dependent and fluctuating roles played by both cooperative and antagonistic selection in the origin and maintenance of reproductive traits.
... Beyond sex-specific coordination between environmental cues and cell signaling, sexspecific life history events contribute to male-female differences in cell signaling. This is exemplified by mating-dependent changes to female physiology and behavior (Avila et al., 2011;Chapman, 2001;Gillott, 2003;Pitnick et al., 2009;Poiani, 2006;Rodríguez-Martínez et al., 2011;Wolfner, 1997;Adams and Wolfner, 2007;Ameku and Niwa, 2016;Apger-MdGlaughon and Wolfner, 2013;Avila and Wolfner, 2009;Carvalho et al., 2006;Cognigni et al., 2011;Hadjieconomou et al., 2020;Harshman et al., 1999;Heifets and Wolfner, 2004;Mattei et al., 2015;Rubinstein and Wolfner, 2013;Sieber and Spradling, 2015;Vargas et al., 2010;Ribeiro and Dickson, 2010;Walker et al., 2015). Importantly, these matinginduced phenotypes have been shown to depend on specific hormonal and cell signaling pathways, indicating that a sex difference in life history events such as mating can be an important way to achieve a sex difference in cell signaling. ...
Male-female differences in many developmental mechanisms lead to the formation of two morphologically and physiologically distinct sexes. Although this is expected for traits with prominent differences between the sexes, such as the gonads, sex-specific processes also contribute to traits without obvious male-female differences, such as the intestine. Here, we review sex differences in developmental mechanisms that operate at several levels of biological complexity – molecular, cellular, organ and organismal – and discuss how these differences influence organ formation, function and whole-body physiology. Together, the examples we highlight show that one simple way to gain a more accurate and comprehensive understanding of animal development is to include both sexes.
... These changes can occur mainly due to two stimuli produced during copulation: ejaculate transfer and mechanical factors. The ejaculate is composed of sperm, male accessory gland products (MAGs; Gillott, 2003;Perry et al., 2013), and secretions produced by the ejaculatory bulb and ducts (Chapman, 2001;Avila et al., 2011). Transfer of sperm can trigger oocyte and embryonic development (Avila et al., 2010;Findlay et al., 2014;Wainwright et al., 2021), whereas the mode of action of MAGs is not known for most species, in some species, these stimuli act on the female nervous system, causing the release of neurosecretions that generate changes in the female (Engelman, 1970;Heifetz and Wolfner, 2004;Yapici et al., 2008;Avila et al., 2012;Rubinstein and Wolfner, 2013;Heifetz et al., 2014). ...
Copulation and/or ejaculate components can alter female physiological state and female post-mating behavior. The objective of the present study was to determine if copulation and male reproductive accessory gland products (MAGs) modify the behavior of female Anastrepha ludens (Loew) and Anastrepha obliqua (Macquart; Diptera: Tephritidae) in response to two stimuli: male-emitted pheromone and oviposition host volatiles. Olfactometry studies revealed that mated females of both A. ludens and A. obliqua have a stronger response for host volatiles compared to unmated females, which have a stronger response for male pheromone. We also examined olfactory responses of females mated to testectomized males who could transfer MAGs but not sperm. In both species, MAGs alone did not cause the change in the olfactory response observed after copulation, unlike what has been found in Ceratitis capitata (Wiedemann). Females mated to testectomized males responded equally to the male sex pheromone or to host volatiles, thus suggesting that the whole ejaculate is needed to elicit the complete behavioral switch in olfactory response. The function of MAGs is still unknown in these two pests of economic importance. The response for host volatiles by mated females has implications for the development of baits and traps that should preferably attract and target this population.
... detrimental to female recipients, as with the love darts of land snails and anti-aphrodisiac seminal peptides of Drosophila fruit flies, both of which mitigate the intensity of sperm competition in female sperm storage organs [3,4]. However, in many cases, males supply and benefit females with nutritious materials such as prey items they have collected or voluminous secretions from male internal/external glands [1,5]. ...
Background
Many male animals donate nutritive materials during courtship or mating to their female mates. Donation of large-sized gifts, though costly to prepare, can result in increased sperm transfer during mating and delayed remating of the females, resulting in higher paternity. Nuptial gifting sometimes causes severe female-female competition for obtaining gifts (i.e., sex-role reversal in mate competition) and selection on females to increase their mating rate, changing the intensity of sperm competition and the resultant paternity gains. We built a theoretical model to simulate such coevolutionary feedbacks between nuptial gift size (male trait) and propensity for multiple mating (female trait). Donation of nuptial gifts sometimes causes development of female persistence trait for gift acquisition. We also analyzed the causes and consequences of this type of traits, taking double receptacles for nutritious seminal gifts, which are known to occur in an insect group with a “female penis” ( Neotrogla spp.), as an illustrative example.
Results
Our individual-based simulations demonstrated that female-female competition for male-derived nutrients always occur when the environment is oligotrophic and mating costs are low for females. However, a positive correlation between donated gift size and the resultant paternity gain was a requisite for the co-occurrence of large gifts and females’ competitive multiple mating for the gifts. When gift donation satisfied female demands and thus resulted in monandry, exaggeration of nuptial gift size also occurred under the assumption that the last male monopolizes paternity. The evolution of double slots for gift acquisition and digestion (female persistence trait) always occurred when males could not satisfy the demands of females for gifts. However, through coevolutionary reduction in male gift size, fixation of this trait in a population drastically reduced the average female fitness.
Conclusion
Sperm usage patterns, which have rarely been examined for animals with nuptial gifts, can be a critical factor for determining the extent of exaggeration in nuptial gifting. Sex-role reversals in mate competition, as a result of donation of nuptial gifts from males to females, can involve the evolution of male-like, persistent traits in females that reduce population productivity, as is the case with persistence traits in males.
... Although we can link female remating behaviour to reduced sperm number, viability and presence in the T. castaneum female reproductive tract (Sales et al., 2018), there is also the possibility that thermal stress denatures male seminal fluid proteins, which influence female remating behaviour in other insects (e.g. Chapman, 2001;Liu & Kubli, 2003). Notably, we can be sure that these changes in female remating behaviour were not due to mating or insemination failure by their previous heatwave-exposed mates, because dissections showed that more than 90% of these males had successfully transferred spermatophores to females, and most females had some, albeit reduced, reproductive output after mating with a heatwave-exposed male. ...
Why is polyandry such a common mating behaviour when it exposes females to a range of significant fitness costs? Here, we investigated whether polyandry protects females against reduced male fertility caused by thermal stress from heatwave conditions. Sperm production and function are vulnerable to heat, and heatwave conditions are forecast to increase as our climate warms, so we examined these effects on female reproduction and mating behaviour in the flour beetle, Tribolium castaneum, a promiscuous ectotherm model in which fertility is damaged by environmental warming. We tested whether polyandrous matings, or polyandrous sperm stores, protect females against reduced male fertility caused by heatwave conditions, and whether females flexibly adjust their remating behaviour to enable fertility rescue. We found that polyandry protected females against reduced male fertility: monogamous matings with males exposed to heatwave conditions halved female offspring production, but opportunities to mate with five of these males allowed normal female reproductive output. By contrast with this fertility improvement following polyandrous mating opportunities, there was no protective benefit for females already carrying sperm stores from multiple males, which suffered similar heatwave damage within the female tract as monogamous sperm stores. Importantly, female polyandry was flexible to male condition, with females showing greater motivation to remate with new males if their previous mate had been damaged by heatwave exposure, enabling a rapid reproductive rescue. Our results reveal that flexible polyandry enables females to rescue their fertility when male reproductive function is compromised by heatwave conditions, a phenomenon that may become more prevalent under climate change.
... This occurs when selection favors sex-specific reproductive strategies that increase the reproductive success of one sex while simultaneously reducing (or constraining) fitness of the other sex (Aloise King, Banks, & Brooks, 2013;Stumpf, Martinez-Mota, Milich, Righini, & Shattuck, 2011). Sexual conflict is frequently displayed and documented in promiscuous species where males exploit female optima in an attempt to increase their own fitness (Barkow & Burley, 1980) through mechanisms such as limiting female mate choice (Chapman, 2018;Clutton-Brock & Parker, 1995;Smuts & Smuts, 1993), or increasing investment/production of offspring for a given reproductive event above the female's optimal level (Chapman, 2001;Haig, 2010). Females exhibit their own adaptations to counter male strategies to co-opt their fitness optima (Chapman, 2018;Mulder & Rauch, 2009). ...
Differential fertility preferences for men and women may provide insights into human sexual conflict. We explore whether pairbonded couples have different preferences for future offspring, which socioecological factors are associated with these preferences, and who achieves their desired fertility over time. We utilise the Indonesia Family Life Survey (IFLS), a longitudinal survey which collected data from 1993 to 2015, to compare desired future fertility for 9655 couples and follow couples who had divergent preferences. The majority of couples (64.8%) want the same number of future offspring. In 20.7% of couples, husbands want more future offspring than their wives, while the reverse occurs in 14.5% of couples. Living in villages with the husband's or the wife's parent(s) is associated with having divergent preferences for future offspring, where there is a higher likelihood that women prefer more offspring than their husbands. When examining fertility outcomes, women, particularly those who marry at older ages, are more likely to achieve their desired preference. Contrary to previous research, we do not find that living near one's natal kin or having increased autonomy increases an individual's likelihood of achieving desired fertility outcomes.
... These morphologically diverse organs have been proposed to contribute to sperm performance, sperm storage and activation, sperm buffering from osmotic and ionic challenges, and production of mating plugs, spermatophores and pheromones [11,12]. Accessory gland fluid can also influence female receptivity and oviposition rates [13][14][15][16]. While accessory gland fluid can markedly alter the chemical micro-environment of sperm and eggs during fertilization, the role of these specialized glands in parental care and antimicrobial protection is still poorly understood. ...
Males of some species possess extra reproductive organs called accessory glands which are outgrowths of the testes or sperm duct. These organs have a well-established role in reproduction; however, they also appear to have other important functions that are less understood. Here, we investigate the function of the highly complex accessory glands of a marine toadfish, Porichthys notatus , a fish with two reproductive male types: large care-providing ‘guarder’ males and small non-caring ‘sneaker’ males. While both male types have accessory glands, guarder male accessory glands are much larger relative to their body size. We show that accessory gland fluids strongly inhibit the growth of bacterial genera associated with unhealthy eggs and have no effect on the growth of strains isolated from healthy eggs. This antibacterial effect was particularly pronounced for extracts from guarder males. Furthermore, we demonstrate that both healthy and unhealthy plainfin midshipman eggs have diverse but distinct microbial communities that differ in their composition and abundance. The highly specific inhibitory capacity of accessory gland fluid on bacteria from unhealthy eggs was robust across a wide range of ecologically relevant temperatures and salinities. Collectively, these ecological and molecular observations suggest a care function for the accessory gland mediated by antimicrobial agents.
... To give but one example in experimental evolution, consider the landmark experimental evolution study in the field of sexual conflict conducted by Holland and Rice (1999). In the fruit fly Drosophila melanogaster, males can harm females through the toxicity of their seminal-fluid proteins (Chapman 2001). To study the evolution of male-induced harm, Holland and Rice (1999) experimentally enforced monogamy for 47 generations in two replicate experimental evolution lines of D. melanogaster, a species that is naturally promiscuous. ...
Discussions of reproducibility are casting doubts on the credibility of experimental outcomes in the life sciences. Although experimental evolution is not typically included in these discussions, this field is also subject to low reproducibility, partly because of the inherent contingencies affecting the evolutionary process. A received view in experimental studies more generally is that standardization (i.e., rigorous homogenization of experimental conditions) is a solution to some issues of significance and internal validity. However, this solution hides several difficulties, including a reduction of external validity and reproducibility. After explaining the meaning of these two notions in the context of experimental evolution, we import from the fields of animal research and ecology and suggests that systematic heterogenization of experimental factors could prove a promising alternative. We also incorporate into our analysis some philosophical reflections on the nature and diversity of research objectives in experimental evolution.
... We also found several seminal fluid associated proteins are evolving exclusively in one species, such as Esterase-6 and Muscleblind in D. arawakana or Lectin-46Cb in D. nigrodunni ( Figure 5, Supplementary Table 6). Inferred through mutant phenotypes, these proteins appear to regulate female receptivity postmating in D. melanogaster (CHAPMAN 2001;BLOCH QAZI et al. 2003;RAVI RAM AND WOLFNER 2005). Though the insemination reaction is not seen in D. melanogaster (ALONSO-PIMENTEL et al. 1994), it is not unreasonable to assume these proteins may play a role in it in other species and could cause the postmating phenotypes we see here (including the toxic effects in hybrid crosses, Figure 3). ...
Proteins involved in post-copulatory interactions between males and females are among the fastest evolving genes in many species, usually attributed to their involvement in reproductive conflict. As a result, these proteins are thought to often be in the formation of postmating-prezygotic incompatibilities between species. The Drosophila dunni subgroup consists of a dozen recently diverged species found across the Caribbean islands with varying levels of hybrid incompatibility. We performed experimental crosses between species in the dunni group and see some evidence of hybrid incompatibilities. We also find evidence of reduced survival following hybrid mating, likely due to postmating-prezygotic incompatibilities. We assessed rates of evolution between these species genomes and find evidence of rapid evolution and divergence of some reproductive proteins, specifically the seminal fluid proteins. This work suggests the rapid evolution of seminal fluid proteins may be associated with postmating-prezygotic isolation, which acts as a barrier for gene flow between even the most closely related species.
... They can also result in the inhibition of sexual receptivity in heterospecific females, leading to fewer rematings with conspecific males. Seminal fluid proteins (Sfps) govern the extent to which heterospecifically mated females increase their egg production, decrease their subsequent receptivity and store or release sperm (Chapman, 2001;Rubinstein & Wolfner, 2013;Sepil et al., 2019;Sirot et al., 2014). As such, Sfps, including their major constituents, the accessory gland proteins (Acps), are predicted to be key determinants of the magnitude and asymmetry of post-mating satyrization effects. ...
The satyr of Greek mythology was half‐man, half‐goat, with an animal persona signifying immoderate sexual appetites. In biology, satyrization is the disruption of reproduction in matings between closely related species. Interestingly, its effects are often reciprocally asymmetric, manifesting more strongly in one direction of heterospecific mating than the other. Heterospecific matings are well known to result in female fitness costs due to the production of sterile or inviable hybrid offspring and can also occur due to reduced female sexual receptivity, lowering the likelihood of any subsequent conspecific matings. Here we investigated the costs and mechanisms of satyrization in the Drosophila melanogaster species subgroup of fruitflies. The results showed that D. simulans females experienced higher fitness costs from a loss of remating opportunities due to significantly reduced post‐mating sexual receptivity than did D. melanogaster females, as a result of reciprocal heterospecific matings. Reciprocal tests of the effects of male reproductive accessory gland protein (Acp) injections on female receptivity in pairwise comparisons between D. melanogaster and five other species within the melanogaster species subgroup revealed significant post‐mating receptivity asymmetries. This was due to variation in the effects of heterospecific Acps within species with which D. melanogaster can mate, and significant but nonasymmetric Acp effects in species with which it cannot. We conclude that asymmetric satyrization due to post‐mating effects of Acps may be common among diverging and hybridising species. The findings are of interest in understanding the evolution of reproductive isolation and species divergence.
... In addition to plug production in some species, SFPs may induce many reproductive female responses that increase male success in sperm competition. These include reduced remating probability, increased ovulation and changes related to sperm transport, use and storage, including action against rival sperm [31,56,95,[97][98][99][100]. Males may adjust their SFP allocation strategically (following predictions for sperm allocation) in relation to the risk or intensity of sperm competition, or female mating status. ...
The past half century has seen the development of the field of post-ejaculatory sexual selection, the sequel to sexual selection for mate-acquisition (pre-ejaculatory) described by Darwin. In richness and diversity of adaptations, post-ejaculatory selection rivals that of pre-ejaculatory sexual selection. Anisogamy—and hence two sexes—likely arose by primeval gamete competition, and sperm competition remains a major force maintaining high sperm numbers. The post-ejaculatory equivalent of male–male competition for matings, sperm competition was an intense ancestral form of sexual selection, typically weakening as mobility and internal fertilization developed in many taxa, when some expenditure became diverted into pre-ejaculatory competition. Sperm competition theory has been relatively successful in explaining variation in relative testes size and sperm numbers per ejaculate and is becoming more successful in explaining variation in sperm phenotype. Sperm competition has generated many other male adaptations such as seminal fluid proteins that variously modify female reproduction towards male interests, and copulatory plugs, prolonged copulations and post-ejaculatory guarding behaviour that reduce female remating probability, many of which result in sexual conflict. This short survey of conceptual developments is intended as a broad overview, mainly as a primer for new researchers.
This article is part of the theme issue ‘Fifty years of sperm competition'.
... Extensive studies in Drosophila melanogaster reveal that these interactions are mediated in part by seminal fluid proteins (SFPs), which are secreted from the paired male accessory glands (AGs) and the ejaculatory bulb (EB) [41]. Some of these proteins induce physiological effects in the mated female, such as increased oviposition [22], facilitation of sperm storage [34], reduction of the female's propensity to remate [50], and reduction of her lifespan [12]. To date about 200 SFPs have been identified in D. melanogaster, and several of these have been shown to evolve rapidly between species of the melanogaster group [9,47]. ...
Postcopulatory sexual selection (PCSS) is a potent evolutionary force that can drive rapid changes of reproductive genes within species, and thus has the potential to generate reproductive incompatibilities between species. Male seminal fluid proteins (SFPs) are major players in postmating interactions, and likely the main targets of PCSS in males. The virilis subgroup of Drosophila exhibits strong interspecific gametic incompatibilities, and can serve as a model to study the genetic basis of PCSS and gametic isolation. However, reproductive genes in this group have not been characterized. Here we use short-read RNA sequencing of male reproductive organs to examine the evolutionary dynamics of reproductive genes in members of the virilis subgroup: D. americana, D. lummei, D. novamexicana , and D. virilis. For each of the three male reproductive organs (accessory glands, ejaculatory bulb, and testes), we identify genes that show strong expression bias in a given tissue relative to the remaining tissues. We find that the majority of male reproductive transcripts are testes-biased, accounting for ~15% of all annotated genes. Ejaculatory bulb-biased transcripts largely code for lipid metabolic enzymes, and contain orthologs of the D. melanogaster ejaculatory bulb protein, Peb-me, which is involved in mating-plug formation. In addition, we identify 71 candidate SFPs, and show that this set of genes has the highest rate of nonsynonymous codon substitution relative to testes- and ejaculatory bulb-biased genes. Furthermore, these SFPs are underrepresented on the X chromosome and are enriched for proteolytic enzymes, which is consistent with SFPs in other insect species. Surprisingly, we find 35 D. melanogaster SFPs with conserved accessory gland expression in the virilis group, suggesting these genes may have conserved reproductive roles in Drosophila. Finally, we show that several of the SFPs that have the highest rate of nonsynonymous codon substitutions reside on the centromeric half of chromosome 2, which contributes to paternal gametic incompatibility between species. Our results suggest that SFPs are under strong selection in the virilis group, and likely play a major role in PCSS and/or gametic isolation.
... Chromosome 19 contained a SNP identified as a candidate for balancing selection within 1 kb of a gene that is closest ortholog is the gene EbpIII that is specifically expressed in the ejaculatory bulb and seminal fluid of D. melanogaster. Balancing selection has been proposed as an explanation for high allelic diversity in a number of seminal fluid accessory proteins (Acps), proteins that influence reproductive traits such as sperm transfer, sperm storage, female receptivity, ovulation and oogenesis (Chapman, 2001). While these are an interesting set of candidate genes for balancing selection in this system, future studies involving more fine-scale genomic resolution and functional assays will help to evaluate these candidates more thoroughly. ...
Hybrid zones are a valuable tool for studying the process of speciation and for identifying the genomic regions undergoing divergence and the ecological (extrinsic) and non-ecological (intrinsic) factors involved. Here, we explored the genomic and geographic landscape of divergence in a hybrid zone between Papilio glaucus and Papilio canadensis . Using a genome scan of 28,417 ddRAD SNPs, we identified genomic regions under possible selection and examined their distribution in the context of previously identified candidate genes for ecological adaptations. We showed that differentiation was genome-wide, including multiple candidate genes for ecological adaptations, particularly those involved in seasonal adaptation and host plant detoxification. The Z-chromosome and four autosomes showed a disproportionate amount of differentiation, suggesting genes on these chromosomes play a potential role in reproductive isolation. Cline analyses of significantly differentiated genomic SNPs, and of species diagnostic genetic markers, showed a high degree of geographic coincidence (81%) and concordance (80%) and were associated with the geographic distribution of a climate-mediated developmental threshold (length of the growing season). A relatively large proportion (1.3%) of the outliers for divergent selection were not associated with candidate genes for ecological adaptations and may reflect the presence of previously unrecognized intrinsic barriers between these species. These results suggest that exogenous (climate-mediated) and endogenous (unknown) clines may have become coupled and act together to reinforce reproductive isolation. This approach of assessing divergence across both the genomic and geographic landscape can provide insight about the interplay between the genetic architecture of reproductive isolation and endogenous and exogenous selection.
Long matings are abundant in insects despite the range of the costs involved. The causes and consequences of the evolution of long matings remain an interesting problem for behavioural ecologists. We studied the Parthenium beetle (Zygogramma bicolorata), which is known to show extraordinarily long copulations. Our detailed investigation showed, for the first time, that the long mounting in this species entails repeated copulation. Each of these copulations is preceded and succeeded by a leg-rubbing behaviour. We found the same characteristic pattern in laboratory and semi-natural conditions. We conducted a series of interrupted mounting assays to examine the fitness consequences of the duration of mounting. We tested multiple hypotheses regarding the transfer of sperm and non-sperm components, and the function of leg rubbing in modulating the female copulatory behaviour. Sperm transfer and fertility did not exhibit a linear increase with the number of copulations. There was also no evidence of nutrient transfer by the males. In contrast, our experiments reveal significant cost of long mounting in these beetles. We showed female remating behaviour can be modulated by the long previous mounting. Our data also suggest that leg rubbing may reduce female resistance to mating. While the long mating possibly serves as copulatory mate guarding, the males may increase their competitive ability through modulating female remating. We also propose leg rubbing to be a copulatory courtship behaviour. Our study provides preliminary insights into the evolution of long mating in such systems and necessitates further research on sexual selection.
While numerous theoretical population genetic models predict that mating assortatively by genetic “quality” will enhance the efficiency of purging of deleterious mutations and/or the spread of beneficial alleles in the gene pool, empirical examples of assortative mating by quality are surprisingly rare and often inconclusive. Here, we set out to examine whether fruit flies (Drosophila melanogaster) engage in assortative mating by body-size phenotype, a composite trait strongly associated with both reproductive success and survival and is considered a reliable indicator of natural genetic quality. Male and female flies of different body-size classes (large and small) were obtained under typical culture conditions, which allows us to use standing variation of body size without involving artificial nutritional manipulation, so that their interactions and mating patterns could be measured. While flies did not exhibit assortative courtship behavior, when patterns of offspring production were analyzed, it was found that individuals produced more offspring with partners of similar quality/body size, resulting produced from disassortative mating. Together, these results validate theoretical predictions that sexual selection can enhance the effects of natural selection and consequently the rate of adaptive evolution in a positive correlation in fitness between mates. Subsequent assays of offspring fitness indicated that assortative mating produced sons and daughters that had greater or equal reproductive success than those
Thermal stress leads to fertility reduction, can cause temporal sterility and thus results in fitness loss with severe ecological and evolutionary consequences, e.g., threatening species persistence already at sub-lethal temperatures. For males we here tested which developmental stage is particularly sensitive to heat stress in the model species Drosophila melanogaster. As developmental stages characterize the different steps of sperm development, we could narrow down which particular processes are heat sensitive. We studied early male reproductive ability and, by following recovery dynamics after a move to benign temperatures, we investigated general mechanisms behind a subsequent gain of fertility. We found strong support to suggest that the last steps of spermatogenesis are particularly sensitive to heat stress, as processes occurring during the pupal stage were mostly interrupted, delaying both sperm production and sperm maturation. Moreover, further measurements in the testes and for proxies of sperm availability indicating the onset of adult reproductive capacity matched the expected heat-induced delay in completing spermatogenesis. We discuss these results within the context of how heat stress affects reproductive organ function and the consequences for male reproductive potential.
Advanced paternal age has been repeatedly shown to modulate offspring quality via male- and/or female-driven processes, and there are theoretical reasons to expect that some of these effects can be sex-specific. For example, sex allocation theory predicts that, when mated with low-condition males, mothers should invest more in their daughters compared to their sons. This is because male fitness is generally more condition-dependent and more variable than female fitness, which makes it less risky to invest in female offspring. Here, we explore whether paternal age can affect the quality and quantity of offspring in a sex-specific way using Drosophila melanogaster as a model organism. In order to understand the contribution of male-driven processes on paternal age effects, we also measured the seminal vesicle size of young and older males and explored its relationship with reproductive success and offspring quality. Older males had lower competitive reproductive success, as expected, but there was no difference between the offspring sex ratio of young and older males. However, we found that paternal age caused an increase in offspring quality (i.e., offspring weight), and that this increase was more marked in daughters than sons. We discuss different male- and female-driven processes that may explain such sex-specific paternal age effects.
Locomotor performance is an indicator of dynamic exercise; thus, it is a central trait in many animal behaviours. Although higher locomotor endurance may increase male reproductive success (e.g., in mate searching and male-male contests), investment in other male reproductive traits (e.g., male attractiveness and sperm competition) may be decreased through energy consumption due to higher activity levels. Here, I investigated male attractiveness, mating success, and paternity success using males of the red flour beetle Tribolium castaneum selected for higher (H) and lower (L) locomotor endurance. Although there was no difference in male attractiveness between the selection regimes, H males had significantly higher mating success than L males. Conversely, L males had significantly higher paternity success than H males. Therefore, there was a trade-off between mating success and paternity success among the selection regimes, suggesting that locomotor endurance affects male reproduction in T. castaneum, and individual variation of locomotor endurance may be maintained within a population.
The interface of sexual behavior and evolutionary psychology is a rapidly growing domain, rich in psychological theories and data as well as controversies and applications. With nearly eighty chapters by leading researchers from around the world, and combining theoretical and empirical perspectives, The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology is the most comprehensive and up-to-date reference work in the field. Providing a broad yet in-depth overview of the various evolutionary principles that influence all types of sexual behaviors, the handbook takes an inclusive approach that draws on a number of disciplines and covers nonhuman and human psychology. It is an essential resource for both established researchers and students in psychology, biology, anthropology, medicine, and criminology, among other fields. Volume 1: Foundations of Evolutionary Perspectives on Sexual Psychology addresses foundational theories and methodological approaches.
The interface of sexual behavior and evolutionary psychology is a rapidly growing domain, rich in psychological theories and data as well as controversies and applications. With nearly eighty chapters by leading researchers from around the world, and combining theoretical and empirical perspectives, The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology is the most comprehensive and up-to-date reference work in the field. Providing a broad yet in-depth overview of the various evolutionary principles that influence all types of sexual behaviors, the handbook takes an inclusive approach that draws on a number of disciplines and covers nonhuman and human psychology. It is an essential resource for both established researchers and students in psychology, biology, anthropology, medicine, and criminology, among other fields. Volume 1: Foundations of Evolutionary Perspectives on Sexual Psychology addresses foundational theories and methodological approaches.
Spermatozoal morphology is highly variable both among and within species and in ways that can significantly impact fertilization success. In Drosophila melanogaster , paternity success depends on sperm length of both competing males and length of the female’s primary sperm storage organ. We found that genes upregulated in long sperm testes are enriched for lncRNAs and seminal fluid proteins (Sfps). Transferred in seminal fluid to the female during mating, Sfps are secreted by the male accessory glands (AG) and affect female remating rate, physiology, and behavior with concomitant advantages for male reproductive success. Despite being upregulated in long sperm testes, they have no known function in testis tissue. We found that Sex Peptide and ovulin (Acp26Aa) knockouts resulted in shorter sperm, suggesting that Sfps may regulate sperm length during spermatogenesis. However, knockout of AG function did not affect sperm length, suggesting that AG expression has no influence on spermatogenic processes. We also found that long sperm males are better able to delay female remating, suggesting higher Sfp expression in AG. These results might suggest that long sperm males have a double advantage in sperm competition by both delaying female remating, likely through transfer of more Sfps, and by resisting sperm displacement. However, we also found that this extra advantage does not necessarily translate to more progeny or higher paternity success. Thus, we found that multiple components of the ejaculate coordinate to promote male reproductive success at different stages of reproduction, but the realized fitness advantages in sperm competition are uncertain.
Significance Statement
The ejaculate is comprised of sperm produced in the testis and seminal fluid primarily produced in the male accessory glands (AG). These complementary components are both critical for male reproductive success, but they are largely considered to be functionally, genetically, and developmentally independent. In a quest to understand genetic mechanisms of sperm length variation, we found that genes upregulated in long sperm testes are enriched for lncRNAs and seminal fluid proteins (Sfps). Knockout of two Sfps, Sex Peptide and ovulin, results in shorter sperm, though knockout of AG function has no effect. Moreover, long sperm males delay female remating longer. These results suggest sophisticated testis-AG coordination that amplifies male reproductive success, with implications for evolutionary integration of sexually selected traits.
Successful reproduction is dependent on the transfer of male seminal proteins to females upon mating. These proteins arise from secretory tissues in the male reproductive tract, including the prostate and seminal vesicles in mammals and the accessory gland in insects. Although detailed functional studies have provided important insights into the mechanisms by which accessory gland proteins support reproduction, much less is known about the molecular mechanisms that regulate their expression within this tissue. Here we show that the Drosophila HR39 nuclear receptor is required for the proper expression of most genes that encode male accessory gland proteins. Consistent with this role, HR39 mutant males are infertile. In addition, tissue-specific RNAi and genetic rescue experiments indicate that HR39 acts within the accessory glands to regulate gene expression and male fertility. These results provide new directions for characterizing the mammalian orthologs of HR39, the SF-1 and LRH-1 nuclear receptors, both of which are required for glandular secretions and reproduction. In addition, our studies provide a molecular mechanism to explain how the accessory glands can maintain the abundant levels of seminal fluid production required to support fertility.
Orphan genes are genes with no sequence homologues in other species. Here, we identified two orphan genes, namely, Tssor-3 and Tssor-4, in Plutella xylostella. Both genes contained a signal peptide sequence, suggesting their functions as secreted proteins. Expression pattern analysis based on real-time quantitative PCR (qPCR) showed that both orphan genes were specifically expressed in all male gonads except the testes. The expression of both the orphan genes peaked at the male adult stage. Immunofluorescence assays suggested that the two proteins were seminal proteins, indicating their potential roles in male reproductive regulation. To further explain their functions, we knocked down the expression of these two genes by RNA interference (RNAi). The results showed that the expression of Tssor-3 and Tssor-4 was significantly downregulated at 24 h after injection compared to that of the controls. Biological assays showed that the number of laid eggs and the hatching rate of offspring eggs were significantly reduced when the expression of Tssor-3 and Tssor-4 was reduced, suggesting that the two orphan genes played a role in male fertility in P. xylostella. Our results provide evidence that orphan genes are involved in male reproductive regulation, which is important for male fitness during evolution.
Conflict between the sexes over control of copulation may drive the coevolution of elaborate genitalia and other secondary sexual structures. Support for this hypothesis is limited to male adaptations that function to enhance male control over females in copulation (e.g. structures that function to clasp females). Evidence for morphological adaptation in females is critical to the hypothesis, yet lacking. Here, we present the first experimental evidence demonstrating that female abdominal spines in water striders function to increase female control over copulation. By experimentally extending the phenotypic size range of these spines, we show that this morphological adaptation, specific to females, allows them to thwart harassing males, and as a result, reduce the frequency of costly matings to females. This demonstrates the coevolutionary nature of sexual conflict and that females are indeed active participants in the evolutionary conflict over control of reproduction.
Different loci within the genome of a single species can potentially coevolve in a manner that is analogous to the Red Queen
process among species. The major factor driving this antagonistic coevolution among loci is intergenomic conflict, i.e., discord
between individuals that is mediated by two or more gene products that are derived from different gene loci. We conclude that
antagonistic coevolution is common among loci that code for social interactions, and that it has broad evolutionary implications,
especially in the context of speciation and sex chromosome evolution.
Identification and annotation of all the genes in the sequenced Drosophila genome is a work in progress. Wild-type testis function requires many genes and is thus of potentially high value for the identification of transcription units. We therefore undertook a survey of the repertoire of genes expressed in the Drosophila testis by computational and microarray analysis. We generated 3141 high-quality testis expressed sequence tags (ESTs). Testis ESTs computationally collapsed into 1560 cDNA set used for further analysis. Of those, 11% correspond to named genes, and 33% provide biological evidence for a predicted gene. A surprising 47% fail to align with existing ESTs and 16% with predicted genes in the current genome release. EST frequency and microarray expression profiles indicate that the testis mRNA population is highly complex and shows an extended range of transcript abundance. Furthermore, >80% of the genes expressed in the testis showed onefold overexpression relative to ovaries, or gonadectomized flies. Additionally, >3% showed more than threefold overexpression at p <0.05. Surprisingly, 22% of the genes most highly overexpressed in testis match Drosophila genomic sequence, but not predicted genes. These data strongly support the idea that sequencing additional cDNA libraries from defined tissues, such as testis, will be important tools for refined annotation of the Drosophila genome. Additionally, these data suggest that the number of genes in Drosophila will significantly exceed the conservative estimate of 13,601.
[The sequence data described in this paper have been submitted to the dbEST data library under accession nos. AI944400 – AI947263 and BE661985 – BE662262 .]
[The microarray data described in this paper have been submitted to the GEO data library under accession nos. GPLS, GSM3–GSM10.]
The seminal fluid that is transferred along with sperm during mating acts in many ways to maximize a male’s reproductive success. Here, we use transgenic Drosophila melanogaster males deficient in the seminal fluid proteins derived from the accessory gland (Acps) to investigate the role of these proteins in the fate of sperm transferred to females during mating. Competitive PCR assays were used to show that while Acps contribute to the efficiency of sperm transfer, they are not essential for the transfer of sperm to the female. In contrast, we found that Acps are essential for storage of sperm by females. Direct counts of stored sperm showed that 10% of normal levels are stored by females whose mates transfer little or no Acps along with sperm.
Mated females of many animal species store sperm. Sperm storage profoundly influences the number, timing, and paternity of the female’s progeny. To investigate mechanisms for sperm storage in Drosophila melanogaster, we generated and analyzed mutations in Acp36DE. Acp36DE is a male seminal fluid protein whose localization in mated females suggested a role in sperm storage. We report that male-derived Acp36DE is essential for efficient sperm storage by females. Acp36DE1 (null) mutant males produced and transferred normal amounts of sperm and seminal fluid proteins. However, mates of Acp36DE1 males stored only 15% as many sperm and produced 10% as many adult progeny as control-mated females. Moreover, without Acp36DE, mated females failed to maintain an elevated egg-laying rate and decreased receptivity, behaviors whose persistence (but not initiation) normally depends on the presence of stored sperm. Previous studies suggested that a barrier in the oviduct confines sperm and Acp36DE to a limited area near the storage organs. We show that Acp36DE is not required for barrier formation, but both Acp36DE and the barrier are required for maximal sperm storage. Acp36DE associates tightly with sperm. Our results indicate that Acp36DE is essential for the initial storage of sperm, and that it may also influence the arrangement and retention of stored sperm.
This article reports the results of some sperm displacement experiments, as well as the results of a theoretical study of selection arising from genetic differences in displacing ability. The experimental work involved the use of three genetic marker stocks in double and triple matings. The speed of displacement following the matings was determined by scoring the progeny of each female daily. There were clear differences between strains in their displacing ability. It is shown how new information concerning the displacement process results when three markers are used; however, no new light is shed by these experiments on the mechanism of displacement.
The theoretical study of selection resulting from displacement uses a one-locus, two-allele model in which three diploid male genotypes confer different displacing abilities. The results indicate stable equilibria if (1) there is heterosis, and (2) there are certain nontransitive relationships in displacing ability among the different kinds of double matings.
Some evolutionary consequences are discussed in which sperm displacement is regarded as a form of sexual selection.
A striking aspect of many vertebrate immune system genes is the exceptionally high level of polymorphism they harbor. A convincing case can be made that this polymorphism is driven by the diversity of pathogens that face selective pressures to evade attack by the host immune system. Different organisms accomplish a defense against diverse pathogens through mechanisms that differ widely in their requirements for specific recognition. It has recently been shown that innate defense mechanisms, which use proteins with broad-spectrum bactericidal properties, are common to both primitive and advanced organisms. In this study we characterize DNA sequence variation in six pathogen defense genes of Drosophila melanogaster and D. mauritiana, including Andropin; cecropin genes CecA1, CecA2, CecB, and CecC; and Diptericin. The necessity for protection against diverse pathogens, which themselves may evolve resistance to insect defenses, motivates a population-level analysis. Estimates of variation levels show that the genes are not exceptionally polymorphic, but Andropin and Diptericin have patterns of variation that differ significantly from neutrality. Patterns of interpopulation and interspecific differentiation also reveal differences among the genes in evolutionary forces.
Paternity of offspring of multiply inseminated females is in many organisms highly skewed, with an advantage generally going to the male that most recently mated. Variation in sperm competitive ability can result in strong natural selection, and one expects that a gene that offers an advantage in sperm displacement would, all else being equal, be rapidly fixed, leaving low equilibrium levels of variability in sperm competition. However, empirical studies have demonstrated genetic variation in sperm displacement, begging the question of how this variation can be maintained. Here we develop a population genetic model to find conditions that maintain polymorphism in alleles that influence sperm displacement. We consider a one-locus model in which allelic variants have pleiotropic effects on fecundity and mating ability in addition to sperm displacement. This model can admit more than one stable polymorphism, and we find conditions for protected polymorphism. Induced overdominance is not necessary for stable polymorphism. These results have direct bearing on the observed variation in the ability of resident sperm to defend against displacement.
Drosophila males, like males of most other insects, transfer a group of specific proteins to the females during mating. These proteins are produced primarily in the accessory gland and are likely to influence the female's reproduction. The results of studies of DNA sequence polymorphism and divergence in two genes coding for male accessory gland proteins of Drosophila are reported here. The Mst26Aa and Mst26Ab transcription units are tandemly arranged in a approximately 1.6-kb segment in Drosophila sechellia, Drosophila mauritiana and Drosophila simulans as they were reported to be in Drosophila melanogaster. The DNA sequences of 10 alleles from D. melanogaster and one allele each from the three sibling species reveals a high degree of amino acid replacement variation. A substantial part of the variation is due to insertion/deletion differences. Possible functional significance of these amino acid sequence changes is discussed. Statistical analyses based on the neutral theory of molecular evolution show that the distribution of polymorphism over the 1.6-kb region is inconsistent with the pattern of divergence between the species. The amount of 4-cutter restriction map polymorphism in a larger sample of 75 alleles from the same D. melanogaster population is similar to that obtained from the DNA sequence of the 10 alleles (a pairwise average of 0.007 difference per site). The 6-cutter restriction map survey of a 18-kb region containing the Mst26A genes indicates that polymorphism in the region flanking these genes maybe higher. The failure of polymorphisms and divergence in the Mst26A region to conform to the expectations of a simple mutation-drift-equilibrium model indicates that selection in or near this region has played a role in the history of these genes.
In this paper we show that when Drosophila melanogaster females are mated twice, the semen of the second male causes a reduction of the effective number of resident sperm from the previous mating. This is demonstrated by two different kinds of experiments. In one set of experiments, mated females were remated to two different kinds of sterile males, one with normal semen and the other with deficient semen. The effect on the resident sperm was determined from the number of remaining progeny after mating to the sterile male, with the result that the normal semen reduced the amount of resident sperm in comparison with matings to the males with deficient semen. The second set of experiments employed interrupted matings. These experiments were based on the observation that semen is delivered before sperm during the first 5 min of copulation. The second matings were interrupted instantly, 2 min, and 4 min after the initiation of copulation. Compared to the instant interruptions, the two later interruptions had the effect of reducing the amount of resident sperm. The results of these two experiments clearly indicate that a sperm-incapacitation process plays a role in the well-documented phenomenon of sperm displacement (last-male advantage) in this species. Such a process could play a role in sperm displacement in the many cases where the mechanism is unknown.
A model of sexual selection that leads to the evolution of exaggerated male display characters that is based on antagonistic coevolution between the sexes is described. The model is motivated by three lines of research: intersexual conflict with respect to mating, sensory exploitation, and the evolution of female resistance, as opposed to preference, for male display traits. The model generates unique predictions that permit its operation to be distinguished from other established models of sexual selection. One striking prediction is that females will frequently win the coevolutionary arms race with males, leaving them encumbered with costly ornaments that have little value except that their absence understimulates females. Examples from the literature suggest that the model may have broad application in nature. The chase-away model is a special case of the more general phenomenon of Interlocus Contest Evolution (ICE).
In this paper, I consider the criteria necessary to demonstrate the postcopulatory ability of females to favor the sperm of one conspecific male over another, that is, sperm choice. In practice it is difficult to distinguish between sperm competition and sperm choice, and sperm choice can be demonstrated only if the effects of sperm competition can be controlled. Few studies have used experimental protocols that do this, so evidence for sperm choice is limited. Moreover, in those studies in which sperm choice occurs, it does so to avoid incompatible genetic combinations and is therefore unlikely to result in directional sexual selection.
Insects and arachnids display the most impressive diversity of mating and social behaviour among all animals. This book investigates sexual competition in these groups, and the variety of ways in which males and females pursue, persuade, manipulate, control and help one another, enabling us to gain a better understanding of how conflicts and confluences of interest evolve together. Each chapter provides a comprehensive review of mating systems in particular insect and arachnid groups, discusses intrinsic and extrinsic factors responsible for observed mating strategies, and suggests fruitful avenues for further research. The book culminates in a synthesis, reviewing the date in terms of the theory of sexual conflict. This broad-based book will be of immense value to students and researchers interested in reproductive strategies, behavioural ecology, entomology and arachnology.
Identification and annotation of all the genes in the sequencedDrosophila genome is a work in progress. Wild-type testis function requires many genes and is thus of potentially high value for the identification of transcription units. We therefore undertook a survey of the repertoire of genes expressed in the Drosophilatestis by computational and microarray analysis. We generated 3141 high-quality testis expressed sequence tags (ESTs). Testis ESTs computationally collapsed into 1560 cDNA set used for further analysis. Of those, 11% correspond to named genes, and 33% provide biological evidence for a predicted gene. A surprising 47% fail to align with existing ESTs and 16% with predicted genes in the current genome release. EST frequency and microarray expression profiles indicate that the testis mRNA population is highly complex and shows an extended range of transcript abundance. Furthermore, >80% of the genes expressed in the testis showed onefold overexpression relative to ovaries, or gonadectomized flies. Additionally, >3% showed more than threefold overexpression at p <0.05. Surprisingly, 22% of the genes most highly overexpressed in testis matchDrosophila genomic sequence, but not predicted genes. These data strongly support the idea that sequencing additional cDNA libraries from defined tissues, such as testis, will be important tools for refined annotation of the Drosophila genome. Additionally, these data suggest that the number of genes in Drosophila will significantly exceed the conservative estimate of 13,601.
[The sequence data described in this paper have been submitted to the dbEST data library under accession nos.AI944400–AI947263 and BE661985–BE662262.]
[The microarray data described in this paper have been submitted to the GEO data library under accession nos. GPLS, GSM3–GSM10.]
In this paper we show that when Drosophila melanogaster females are mated twice, the semen of the second male causes a reduction of the effective number of resident sperm from the previous mating. This is demonstrated by two different kinds of experiments. In one set of experiments, mated females were remated to two different kinds of sterile males, one with normal semen and the other with deficient semen. The effect on the resident sperm was determined from the number of remaining progeny after mating to the sterile male, with the result that the normal semen reduced the amount of resident sperm in comparison with matings to the males with deficient semen. The second set of experiments employed interrupted matings. These experiments were based on the observation that semen is delivered before sperm during the first 5 min of copulation. The second matings were interrupted instantly, 2 min, and 4 min after the initiation of copulation. Compared to the instant interruptions, the two later interruptions had the effect of reducing the amount of resident sperm. The results of these two experiments clearly indicate that a spermincapacitation process plays a role in the well-documented phenomenon of sperm displacement (last-male advantage) in this species. Such a process could play a role in sperm displacement in the many cases where the mechanism is unknown.
Progeny production and sperm use in D. melanogaster were analyzed with attention to the different effects contributed by males containing the putative reproductive enzyme, EST 6, and males lacking it. A stochastic model of daily progeny production, framed in terms of an exponential egg growth phase and an exponential decay in sperm release, was proposed to explain the two primary components of productivity. The model fit well to observed production and permitted a quantitative analysis of differences in the form of daily productivity due to EST 6, where no differences were found in total productivities of these males. This model analysis suggested that release of stored sperm differed due to EST 6, in particular that the initial number of stored sperm was lower, and the exponential rate of release was slower when EST 6 was present. Sperm counts undertaken to determine the validity of this sperm release hypothesis and the existence of sperm use differences due to EST 6 revealed a complex pattern of sperm use. The primary features of this usage pattern are: an initially high release of sperm leading to significant sperm wastage; an exponential decline in storage with time as predicted by random release of sperm from storage; a sudden high rate of release from the receptacle starting at about the time of declining fertility; and an initially higher rate of sperm release due to EST 6. This initial rapid release effect of EST 6 is interpreted in the light of other information about this enzyme and of sperm use relationships to suggest that it acts as a sperm displacement-release enzyme. The primary adaptive significance of EST 6 to male Drosophila would be in terms of the balance he strikes between displacing sperm of another male and wasting his own.
The period of initial sperm storage and use by Drosophila melanogaster females is examined for effects of the seminal fluid enzyme esterase 6. Females mated to males differing in their level of esterase 6 activity were dissected from 5 min to 50 hr after the start of copulation and numbers of sperm contained in the uterus, ventral receptacle and paired spermathecae were counted. Of the 4000–6000 sperm transferred at copulation, about 700 are stored in the receptacle by 4 hr post mating and 400 in the spermathecae by 7 hr. However, sperm are released rapidly from storage organs following these peaks and may be found again in the uterus in numbers up to 100 or more. The rate of sperm release is closely related to the level of esterase 6 activity, suggesting that this seminal fluid enzyme is involved in sperm motility.
In methanolic extracts of accessory glands (paragonia) from Drosophila funebris, two specific, ninhydrin-positive substances, PS-1 and PS-2, were found. PS-1 and PS-2 were isolated by column chromatography. PS-1 consists of 27 amino acid residues. Two forms of PS-1 are present in the ratio of 7:3 which differ only in the content of valine and leucine. Fractions containing partially purified valine-PS-1 and leucine-PS-1, respectively, have the same biological activity. All males in the population synthesize both forms of PS-1. PS-2 is a low molecular weight substance containing glycine and ammonia as ninhydrin-positive components and carbohydrate as indicated by several sugar tests. In vitro studies showed that copulation provides the stimulus for enhanced synthesis of paragonial substances.
The substance, PS-1, produced in the paragonial gland of adult male Drosophila funebris influences the mating behavior of virgin female flies after injection. The substance was isolated and characterized as a 27-residue peptide. The complete amino acid sequence was determined by manual sequence analysis of tryptic peptides, automated Edman degradation, and carboxypeptidase A digestion. The sequence is Asp-ValLeu-Pro-Ser-Ala-Asn-Ala-Asn-Ala-Asn-Asn-Gln-Arg-Thr-Ala-Ala-Ala-Lys-Pro-Gln-Ala-Asn-Ala-Glu-Ala-Ser-Ser. The ratio of Val: Leu in the second position of the sequence is 7:3. This is the first detailed report on an insect peptide which causes a biological response in the opposite sex following mating.
In many sexually mature insects egg production and oviposition are tightly coupled to copulation. Sex-Peptide is a 36-amino-acid peptide synthesized in the accessory glands ofDrosophila melanogastermales and transferred to the female during copulation. Sex-Peptide stimulates vitellogenic oocyte progression through a putative control point at about stage 9 of oogenesis. Here we show that application of the juvenile hormone analogue methoprene mimics the Sex-Peptide-mediated stimulation of vitellogenic oocyte progression in sexually mature virgin females. Apoptosis is induced by 20-hydroxyecdysone in nurse cells of stage 9 egg chambers at physiological concentrations (10−7M). 20-Hydroxyecdysone thus acts as an antagonist of early vitellogenic oocyte development. Simultaneous application of juvenile hormone analogue, however, protects early vitellogenic oocytes from 20-hydroxyecdysone-induced resorption. These results suggest that the balance of these hormones in the hemolymph regulates whether oocytes will progress through the control point at stage 9 or undergo apoptosis. These data are further supported by a molecular analysis of the regulation of yolk protein synthesis and uptake into the ovary by the two hormones. We conclude that juvenile hormone is a downstream component in the Sex-Peptide response cascade and acts by stimulating vitellogenic oocyte progression and inhibiting apoptosis. Since juvenile hormone analogue does not elicit increased oviposition and reduced receptivity, Sex-Peptide must have an additional, separate effect on these two postmating responses.
We suggest that damaging mating tactics, such as physical aggression, the evolution of genital barbs and spines, and the transfer of seminal toxins may serve as a general means by which males can induce females to avoid or to delay remating. Provided that cu- mulative damage has an accelerating impact on fitness, a female who has already been harmed by previous partner(s) may do best to refrain from remating to avoid suffering still further damage. Con- sequently, a male can gain through the imposition of mating costs, even though this may reduce female fitness because by doing so he minimizes the chances that his mate will copulate again. We develop a game theoretical model of this possibility, focusing on toxin transfer as an illustrative example. We show that toxicity as a means of in- hibiting remating is phenotypically stable over a broad range of con- ditions (although, under some circumstances, it may be necessary to invoke other selective pressures to account for the initial evolution of toxicity). The model predicts that toxin transfer should be more common (and involve greater levels of toxicity) in species with greater last-male mating advantage; it is also most likely where the poison inflicts strongly accelerating, dose-dependent costs on females.
An analytical model was used to explore the effect of X-linkage on the evolution of sexual dimorphism. The model examined the requisite conditions for increase when rare, and the equilibrium frequency of genes that produce a 'sexually-antagonistic' phenotype, ie a phenotype that is selectively favored in one sex but disfavored in the other sex. A simulation model was used to examine the evolution of sex-limited modifier genes that restrict the expression of sexually-antagonistic genes in the sex where they are selected against. Sex chromosomes appear to facilitate the evolution of sexual dimorphism and X-linked genes have a predominant role in coding for sexually dimorphic traits.-from Author
The "sexy-sperm" hypothesis proposes that multiple-mating females have a selective advantage over single-mating females because the former are fertilized by the most competitive sperm and have sons that produce competitive sperm. A deterministic genetical model of the sexy-sperm process is described here. It assumes one locus that influences sperm competitive ability and a second locus that influences female mating behavior. The conditions for sperm competition to promote the evolution of multiple mating in females are very restrictive: there must be tight linkage between the two loci, positive linkage disequilibrium, and no fitness cost associated with multiple mating. Any trait (even single-mating female behavior) can increase by hitchhiking if it carries no cost and is under the control of a locus that is tightly linked to the positively selected sperm competition locus. When there are costs for multiple mating, the sexy-sperm mechanism fails: the multiple-mating tendency increases initially but is eliminated when linkage disequilibrium decays. Linkage disequilibrium, rather than intergenerational payoff, is the driving force in this model. Under the assumptions of this model, sperm competition plays no special role in the evolution of female mating frequency.
A model of sexual selection that leads to the evolution of exaggerated male display characters that is based on antagonistic coevolution between the sexes is described. The model is motivated by three lines of research: intersexual conflict with respect to mating, sensory exploitation, and the evolution of female resistance, as opposed to preference, for male display traits. The model generates unique predictions that permit its operation to be distinguished from other established models of sexual selection. One striking prediction is that females will frequently win the coevolutionary arms race with males, leaving them encumbered with costly ornaments that have little value except that their absence understimulates females. Examples from the literature suggest that the model may have broad application in nature. The chase-away model is a special case of the more general phenomenon of Interlocus Contest Evolution (ICE).
Abstract Several recent studies suggest that interactions with conspecific males can reduce the longevity of female Drosophila melanogaster or support the idea that male and female fitness components are involved in antagonistic interactions. Here we report that males from third-chromosome isogenic lines demonstrated significant genetic variation in male reproductive performance and in the longevity of their mates. Increased male performance was marginally significantly associated with one measure of increased female survival rate. However, there was no indication of tradeoffs or negative correlations between male reproductive success and female survival. We discuss alternative hypotheses for the cause of the induced variation in female longevity.
Recent results from biochemical and molecular genetic studies of the accessory gland proteins in maleDrosophila are reviewed. The most prominent feature is the species-specific variability. However, the analysis of the sex peptide inD. melanogaster shows that there is a strong homology in the molecular structure to the closely related sibling species, and that divergence increases with increasing phylogenetic distance. For this reason the sex peptide, after being transferred to the female genital tract during copulation, reduces receptivity and increases oviposition only in virgin females belonging to the same species group and subgroup. Even though studies were hitherto limited to a small number of the secretory components, it is evident that the accessory gland proteins play a key role in reproductive success of the fruit fly by changing female sexual behavior, supporting sperm transfer, storage and displacement. Thus, genes encoding the accessory gland proteins are apparently under strong evolutionary selection.
The ovarian state of Drosophila melanogaster females from a wild population in the south of France was studied by immediate dissection, in the field, during two different periods in the year: early in June and at the end of September. It was compared with either the reproductive capacities of aliquot females kept in laboratory conditions or the reproductive potential of the first laboratory generation.
Among the wild flies, about 20% were young (less than 24 h). 85 to 90% of all females were inseminated and virgins were found among the youngest ones.
In the field, the vitellogenetic activity appeared to be very low and noncontinuous. Females with active vitellogenesis were fairly rare but about 60% of the females presented eggs in retention in the ovaries and 50% had a fertilized egg waiting in the uterus. All these observations showed that fecundity in the field was certainly low.
When wild females were studied in the laboratory, their daily egg production was relatively high, more than 50 eggs per day per female. This production was stimulated by insemination and decreased with adult population density.
Daughter females reared in the laboratory were bigger, had more numerous ovarian tubes than their mothers (an average of 50 instead of 32), and their daily egg production was very high. However the daily overiole production in these two groups was very similar.
The genetic reproductive potential of this natural French population seems to be very high but, under natural life conditions, this potential is not expressed. Wild flies do not seem to give priority to their reproductive effort but to individual survival and activity.
Twelve genomic clones containing sequences complementary to male-specific trancripts were isolated from a library of Drosophila melanogaster. They define five gene regions which were localized by in situ hybridization at 51F, 57D, 75C, 87F, and 95F. The region at 75C contains a small gene family for a male-specific transcript whereas all other coding sequences are represented only once in the genome. Four of the male-specific RNAs accumulate in the male accessory gland while the fifth (localized at 87F) is transcribed in the male germ cells.
Previous studies have shown that the esterase 6 (EST6) enzyme ofD. melanogaster is mainly produced in the sperm ejaculatory duct of the adult male and comparisons of wild-type males with laboratory null mutants have suggested that the enzyme plays a role in reproductive fitness. In this study we have compared 18 field-derived lines each isoallelic forEst6 for differences in five components of male reproductive fitness. No consistent fitness differences were found among lines differing in respect of the two major allozyme classes EST6-F and EST6-S, despite other evidence that these two classes are not selectively equivalent in the field. However, differences in reproductive fitness were found among lines differing in the minor mobility variants that segregate within EST6-F and EST6-S. A failure to distinguish among these minor forms may explain the discrepancies in previous studies on the effects of the major EST6 allozymes on reproductive fitness. The most significant associations we have found between EST6 and reproductive fitness were due to variation in EST6 activity levels. Male EST6 activity levels were found to be positively correlated with their time to first mating, negatively correlated with the numbers of eggs laid and progeny produced by their mates, and negatively correlated with the frequency with which their mates remate. We conclude that some EST6 variants differ in components of male reproductive fitness operative in laboratory cultures. However, the evidence for fitness differences is stronger for variants affecting the amount, rather than the structure of the enzyme, and the direction of the differences varies between some of the fitness components tested.
Males of many insect species transfer, within the ejaculate, substances that render females sexually unreceptive and promote ovulation and oviposition. In this paper, I propose hypotheses for the evolutionary origin of these substances and discuss how selection may have modified them subsequently. Two hypotheses are considered. According to the handicap hypothesis, receptivity inhibition substances (RIS) and ovulation and oviposition stimulating substances (OSS) are used by females to evaluate the quality of the ejaculate received, the last being a function of the genetic or phenotypic quality of sperm, and of the nutritional or protective (to the female or her offspring) quality of its chemical constituents. This hypothesis predicts that RIS and OSS must be reliable indictors of ejaculate quality, reliability being the result of the high RIS/OSS production costs and specific chemical composition. The second hypothesis proposes that RIS/OSS are selected only in regard to their effectiveness as stimulators through Fisher's sexual selection runaway process. According to this hypothesis, RIS/OSS are not necessarily are reliable indicators of sperm or ejaculate chemical constituents quality (other than ability to stimulate), and must show a high species-specificity (rapid evolutionary divergence). Empirical evidence is reviewed, and the kind of information necessary to evaluate the relative importance of each hypothesis is indicated.
Esterase 6 is a non-specific carboxylesterase (EC 3.1.1.1) and is a component of the seminal fluid of Drosophila melanogaster. Previous studies showed the presence of this enzyme in seminal fluid is associated with a variety of effects on female reproductive behaviour and physiology. In the present experiments, male-derived esterase 6 was initially transferred into the female's reproductive tract but was translocated within minutes of the beginning of mating into the haemolymph. Seminal-fluid esterase 6 was detected by Western blot analyses in mated-female haemolymph for as long as 4 days after mating. These results show that the enzyme remains in females for a period long enough to account for many of its behavioural and physiological effects.
In many insect species, sperm transferred in a single mating are stored by the female in specialized organs and are gradually used to fertilize eggs. Thus, insects must have mechanisms to ensure that substantial numbers of sperm reach and become stored in the storage organs. We report here that a glycoprotein, Acp36DE, made by the accessory glands of Drosophila melanogaster males, shows localization in the mated female suggesting a role in sperm storage. In the mated female, Acp36DE associates with the wall of the oviduct, just anterior to the openings of the sperm storage organs. Acp36DE also associates with the leading edge of the sperm mass. It does not enter the hemolymph. Complete localization of Acp36DE in the mated female requires sperm and the presence of eggs in the ovaries. We hypothesize that Acp36DE, or a complex containing it, forms a barrier that “corrals” sperm near the openings to the sperm storage organs. Concentration of sperm here could facilitate their efficient storage. Acp36DE remains in the genital tract for several hours after mating, concurrent with the time that sperm are being stored. Facilitation of sperm storage by Acp36DE may also explain the previously observed effect of this protein on sperm competition.
The accessory gland of male insects produces components of the seminal fluid that alter the behavior, physiology and life span of the mated female, and contribute to her efficient storage and utilization of sperm. As a step towards understanding how this occurs, we have isolated genes encoding 12 previously unreported accessory gland-specific mRNAs from the fruit fly Drosophila melanogaster. We report here the restriction maps of the new genes, the chromosome positions — which are all autosomal — of the 11 non-repetitive genes, their expression patterns, and the sequences of the accessory gland proteins (Acps) encoded by nine of the genes. Eight of the proteins predicted from these sequences begin with putative secretion signals. Following their signal sequences, three of the predicted molecules are peptides and the other five are larger polypeptides with characteristics of cleavable prohormones. The ninth molecule, which has an N-terminal hydrophobic region but no consensus signal peptide cleavage site, is predicted to be a 716 amino acid glycoprotein. Of the nine proteins, two have intriguing similarities to sequences in protein databases. Acp76A is a 388 amino acid pro-protein which contains a signature sequence for the serpin class of protease inhibitors. The 115 amino acid Acp62F has a 28 amino acid region of high sequence similarity to a neurotoxin of the Brazilian armed spider Phoneutria nigriventer. Models are discussed in which Acp76A plays a role in the observed regulation of Acp proteolysis and/or in the coagulation of seminal fluid to form a mating plug, and in which Acp62F contributes to the reported toxicity of Drosophila seminal fluid.
Female D. melanogaster kept with males had lower survival rates than virgins. Inseminated females initially laid significantly more eggs and, later in life, significantly fewer eggs than virgins. Addition of males to virgins resulted after a lag both in a decrease in egg-laying and an increase in death rates, but neither became identical to those of inseminated females before the latter group went extinct. Removal of males from inseminated females resulted after a lagin reversion to the egg-laying and death rates of virgins of the same age. The effects of males on both egg-laying and survival rates were therefore reversible, and not due to an acceleration of senescence. The effect of males on female survival rates could not be explained in terms of the numbers of eggs laid, so that either inseminated and virgin females must produce qualitatively different eggs or males must exert their effect on survival in some other way. Carbon dioxide anaesthesia was without effect on female survival or fertility.
The electrophoretic protein pattern of the male accessory gland in Drosophila sechellia differs from those in the sibling species D. melanogaster, D. simulans and D. mauritiana. The male-specific sex peptides isolated from D. melanogaster and D. sechellia are qually efficient in repressing female sexual receptivity in these four sibling species, but have no effect on females of a distantly related species D. funebris. Sequencing of the sechellia-peptide shows that it consists of 36 amino acids and differs from the melanogaster-peptide reported previously only in three amino acids at positions 8, 11 and 12.
An ovulation stimulating substance (OSS) was isolated from males of the fruit fly Drosophila suzukii, and purified to a homogeneous state by a 5-step purification procedure: extraction with 80% methanol, chloroform wash, heat treatment, ion-exchange chromatography, and reverse phase high performance liquid chromatography. Approximately 100-fold purification was obtained thereby yielding 39 μg of OSS from 1000 males for an overall yield of 34%. The OSS is a single peptide consisting of at least 35 amino acid residues and having a molecular weight of 3990. The purified OSS not only initiated ovulation in unmated females but also suppressed their receptivity towards males. The peptide of D. suzukii was found to be effective in the females of D. melanogaster, a species that belong to a different subgroup, but was less effective in a more closely related species, D. pulchrella.
In this paper, I consider the criteria necessary to demonstrate the postcopulatory ability of females to favor the sperm of one conspecific male over another, that is, sperm choice. In practice it is difficult to distinguish between sperm competition and sperm choice, and sperm choice can be demonstrated only if the effects of sperm competition can be controlled. Few studies have used experimental protocols that do this, so evidence for sperm choice is limited. Moreover, in those studies in which sperm choice occurs, it does so to avoid incompatible genetic combinations and is therefore unlikely to result in directional sexual selection.
Seminal fluid proteins from males of many insect species affect the behavior and physiology of their mates. In some cases, these effects result from entry of the proteins into the female's circulatory system. In the fruit fly Drosophila melanogaster, some seminal fluid proteins enter the female's circulatory system after transfer from the male while others remain confined within the reproductive tract. To address where and how seminal fluid proteins enter the hemolymph of the mated female, we compared the kinetics of transfer and localization in mated females of two seminal fluid proteins that enter the hemolymph (Acp26Aa and Acp62F) and one that does not (Acp36DE). We also generated transgenic flies that produce Acp26Aa tagged with Aequorea victoria green fluorescent protein (GFP) to monitor its transfer in vivo. We report that Acps enter the female circulatory system from the posterior vagina immediately after insemination. The ability of Acps to enter the female hemolymph correlates with their ability to cross the intima that lines the posterior vagina. The ventral posterior vagina is structurally unlike other parts of the female reproductive tract in that it lacks muscles. We hypothesize that it has higher permeability thus affording access to the female's circulatory system.
A 3.1-kb region of Drosphila subobscura homologous to the Acp70A region of D. melanogaster, which contains the sex-peptide gene, was cloned and sequenced. This region contains an approximately 600-bp duplication that includes the sex-peptide and its 5' and 3' flanking regions. The preproteins are 54 and 56 amino acids long, respectively (as compared to 55 amino acids in D. melanogaster), and each includes a 19-amino-acid-long signal peptide. The C-terminal part of the mature peptide is highly conserved between D. melanogaster and the two copies of D. subobscura. In this species, both copies of the gene are transcribed and, like in D. melangaster, only expressed in males. The duplicated region includes 300 bp upstream of the gene that would therefore seem sufficient for their expression in males. This region presents at its 5' end a stretch 93-bp that has a high similarity with the corresponding region of D. melanogaster and could be part of a still unidentified regulatory element of these genes.
Selection clearly focuses on differences in reproduction, but studies of reproductive physiology generally have been carried out in a near vacuum of modern evolutionary theory. This lack of contact between the two fields may be about to change. New ideas indicate that sexual selection by cryptic female choice has affected the evolution of products in male semen that influence female reproductive behavior and physiology.