[Show abstract][Hide abstract] ABSTRACT: Quantifying the shape and strength of mating preferences is a vital component of the study of sexual selection and reproductive isolation, but the influence of experimental design on these estimates is unclear. Mating preferences may be tested using either no-choice or choice designs, and these tests may result in different estimates of preference strength. However, previous studies testing for this difference have given mixed results. To quantify the difference in the strength of mating preferences obtained using the 2 designs, we performed a meta-analysis of 38 studies on 40 species in which both experimental designs were used to test for preferences in a single species/trait/sex combination. We found that mating preferences were significantly stronger when tested using a choice design compared with a no-choice design. We suggest that this difference is due to the increased cost of rejecting partners in no-choice tests; if individuals perceive they are unlikely to remate in a no-choice situation they will be more likely to mate randomly. Importantly the use of choice tests in species in which mates are primarily encountered sequentially in the wild may lead to mating preferences being significantly overestimated. Furthermore, this pattern was seen for female mate choice but not for male mate choice, and for intraspecific choice but not for interspecies or interpopulation mate discrimination. Our study thus highlights the fact that the strength of mating preferences, and thus sexual selection, can vary significantly between experimental designs and across different social and ecological contexts.
[Show abstract][Hide abstract] ABSTRACT: Despite the diverse array of mating systems and life histories which characterise the parasitic Hymenoptera, sexual selection and sexual conflict in this taxon have been somewhat overlooked. For instance, parasitoid mating systems have typically been studied in terms of how mating structure affects sex allocation. In the past decade, however, some studies have sought to address sexual selection in the parasitoid wasps more explicitly and found that, despite the lack of obvious secondary sexual traits, sexual selection has the potential to shape a range of aspects of parasitoid reproductive behaviour and ecology. Moreover, various characteristics fundamental to the parasitoid way of life may provide innovative new ways to investigate different processes of sexual selection. The overall aim of this review therefore is to re-examine parasitoid biology with sexual selection in mind, for both parasitoid biologists and also researchers interested in sexual selection and the evolution of mating systems more generally. We will consider aspects of particular relevance that have already been well studied including local mating structure, sex allocation and sperm depletion. We go on to review what we already know about sexual selection in the parasitoid wasps and highlight areas which may prove fruitful for further investigation. In particular, sperm depletion and the costs of inbreeding under chromosomal sex determination provide novel opportunities for testing the role of direct and indirect benefits for the evolution of mate choice.
Biological reviews of the Cambridge Philosophical Society 07/2014; · 6.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mate choice has long been appreciated as a key component of sexual selection. However, how we measure mate choice, both in the field and in the laboratory, remains problematic. Mating preferences may be tested using either no-choice or choice tests, but explicit comparisons between these two experimental paradigms remain limited. It has been suggested that preferences may be stronger in choice tests as they allow simultaneous comparison, and some studies have indeed found stronger mating preferences in choice tests compared to no-choice tests. Here we explicitly tested the effect of experimental choice paradigm on the measurement of sexual selection on male and female morphology in the promiscuous seed bug Lygaeus equestris (Heteroptera, Lygaeidae). We performed mating trials in which we varied the amount of choice presented to each sex, giving four choice treatments: no-choice, male choice, female choice and mutual choice. Overall we found evidence for significant positive directional selection on female body length and stabilizing selection on an overall measure of male body size. However, we found no significant effect of choice paradigm on the patterns of sexual selection for males or females. We suggest this may be because of the method of mate assessment in L. equestris, which appears to be primarily via contact cues, which may limit simultaneous comparison between options.
[Show abstract][Hide abstract] ABSTRACT: Niche construction refers to the activities of organisms that bring about changes in their environments, many of which are evolutionarily and ecologically consequential. Advocates of niche construction theory (NCT) believe that standard evolutionary theory fails to recognize the full importance of niche construction, and consequently propose a novel view of evolution, in which niche construction and its legacy over time (ecological inheritance) are described as evolutionary processes, equivalent in importance to natural selection. Here, we subject NCT to critical evaluation, in the form of a collaboration between one prominent advocate of NCT, and a team of skeptics. We discuss whether niche construction is an evolutionary process, whether NCT obscures or clarifies how natural selection leads to organismal adaptation, and whether niche construction and natural selection are of equivalent explanatory importance. We also consider whether the literature that promotes NCT overstates the significance of niche construction, whether it is internally coherent, and whether it accurately portrays standard evolutionary theory. Our disagreements reflect a wider dispute within evolutionary theory over whether the neo-Darwinian synthesis is in need of reformulation, as well as different usages of some key terms (e.g. evolutionary process). This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Linking behavioural phenotypes to their underlying genotypes is crucial for uncovering the mechanisms that underpin behaviour and for understanding the origins and maintenance of genetic variation in behaviour. Recently, interest has begun to focus on the transcriptome as a route for identifying genes and gene pathways associated with behaviour. For many behavioural traits studied at the phenotypic level, we have little or no idea of where to start searching for "candidate" genes: the transcriptome provides such a starting point. Here we consider transcriptomic changes associated with oviposition in the parasitoid wasp Nasonia vitripennis. Oviposition is a key behaviour for parasitoids, as females are faced with a variety of decisions that will impact offspring fitness. These include choosing between hosts of differing quality, as well as making decisions regarding clutch size and offspring sex ratio. We compared the whole-body transcriptomes of resting or ovipositing female Nasonia using a "DeepSAGE" gene expression approach on the Illumina sequencing platform. We identified 332 tags that were significantly differentially expressed between the two treatments, with 77% of the changes associated with greater expression in resting females. Oviposition therefore appears to focus gene expression away from a number of physiological processes, with gene ontologies suggesting that aspects of metabolism may be down-regulated during egg-laying. Nine of the most abundant differentially expressed tags showed greater expression in ovipositing females though, including the genes purity-of-essence (associated with behavioural phenotypes in Drosophila) and glucose dehydrogenase (GLD). The GLD protein has been implicated in sperm storage and release in Drosophila and so provides a possible candidate for the control of sex allocation by female Nasonia during oviposition. Oviposition in Nasonia therefore clearly modifies the transcriptome, providing a starting point for the genetic dissection of oviposition.
PLoS ONE 07/2013; 8(7):e68608. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Understanding variation in social behaviour both within and among species continues to be a challenge. Evolutionary or ecological theory typically predicts the optimal behaviour for an animal under a given set of circumstances, yet the real world presents much greater variation in behaviour than predicted. This variation is apparent in many social and sexual interactions, including mate choice, and has led to a renewed focus on individual variation in behaviour. Here we explore within and among species variation in social behaviour in four species of aposematic seed bug (Lygaeidae: Hemiptera). These species are Müllerian mimics, with characteristic warning colouration advertising their chemical toxicity. We examine the role of diet in generating variation in two key behaviours: social aggregation of nymphs and mate choice. We test how behaviour varies with exposure to either milkweed (a source of defensive compounds) or sunflower (that provides no defence). We show that although the four species vary in their food preferences, and diet influences their life-history (as highlighted by body size), social aggregation and mate choice is relatively unaffected by diet. We discuss our findings in terms of the evolution of aposematism, the importance of automimicry, and the role of diet in generating behavioural variation.
[Show abstract][Hide abstract] ABSTRACT: Highlights
► We survey 47 sexual cannibalism papers and note words describing males and females. ► Active words are more likely to be used to describe females than males. ► This contrasts with the findings of a previous study on sexual conflict literature. ► Females were often associated with negative stereotypes. ► Researchers are influenced by their study systems, not just cultural stereotypes.
[Show abstract][Hide abstract] ABSTRACT: Host-parasite interactions are a key paradigm for understanding the process of coevolution. Central to coevolution is how genetic variation in interacting species allows parasites to evolve manipulative strategies. However, genetic variation in the parasite may also be associated with host phenotype changes, thereby changing the selection on both species. For instance, parasites often induce changes in the behaviour of their host to maximize their own fitness, yet the quantitative genetic basis for behavioural manipulation has not been fully demonstrated. Here, we show that the genotype of the parasitoid wasp Aphidius ervi has a significant effect on where its aphid host Acyrthosiphon pisum moves to die following parasitism, including the likelihood that the aphid abandons the plant. These results provide a clear example of an interspecific indirect genetic effect whereby the genetics of one species influences the expression of a specific behavioural trait in another.
[Show abstract][Hide abstract] ABSTRACT: The ability of animals to remember the what, where and when of a unique past event is used as an animal equivalent to human episodic memory. We currently view episodic memory as reconstructive, with an event being remembered in the context in which it took place. Importantly, this means that the components of a what, where, when memory task should be dissociable (e.g. what would be remembered to a different degree than when). We tested this hypothesis by training hummingbirds to a memory task, where the location of a reward was specified according to colour (what), location (where), and order and time of day (when). Although hummingbirds remembered these three pieces of information together more often than expected, there was a hierarchy as to how they were remembered. When seemed to be the hardest to remember, while errors relating to what were more easily corrected. Furthermore, when appears to have been encoded as a combination of time of day and sequence information. As hummingbirds solved this task using reconstruction of different memory components (what, where and when), we suggest that similar deconstructive approaches may offer a useful way to compare episodic and episodic-like memories.
Proceedings of the Royal Society B: Biological Sciences 01/2013; 280(1772):20132194. · 5.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is an extraordinary diversity in genetic systems across species, but this variation remains poorly understood. In part, this is because the mechanisms responsible for transitions between systems are often unknown. A recent hypothesis has suggested that conflict between hosts and endosymbiotic microorganisms over transmission could drive the transition from diplodiploidy to systems with male haploidy (haplodiploidy, including arrhenotoky and paternal genome elimination [PGE]). Here, we present the first formal test of this idea with a comparative analysis across scale insects (Hemiptera: Coccoidea). Scale insects are renowned for their large variation in genetic systems, and multiple transitions between diplodiploidy and haplodiploidy have taken place within this group. Additionally, most species rely on endosymbiotic microorganisms to provide them with essential nutrients lacking in their diet. We show that species harboring endosymbionts are indeed more likely to have a genetic system with male haploidy, which supports the hypothesis that endosymbionts might have played a role in the transition to haplodiploidy. We also extend our analysis to consider the relationship between endosymbiont presence and transitions to parthenogenesis. Although in scale insects there is no such overall association, species harboring eukaryote endosymbionts were more likely to be parthenogenetic than those with bacterial symbionts. These results support the idea that intergenomic conflict can drive the evolution of novel genetic systems and affect host reproduction.
Ecology and Evolution 05/2012; 2(5):1071-81. · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sex ratio theory has been very successful in predicting under which circum- stances parents should bias their investment towards a particular offspring sex. However, most examples of adaptive sex ratio bias come from species with well-defined mating systems and sex determining mechanisms, while in many other groups there is still an on- going debate about the adaptive nature of sex allocation. Here we study the sex allocation in the mealybug Planococcus citri, a species in which it is currently unclear how females adjust their sex ratio, even though experiments have shown support for facultative sex ratio adjustment. Previous work has shown that the sex ratio females produce changes over the oviposition period, with males being overproduced early and late in the laying sequence. Here we investigate this complex pattern further, examining both the robustness of the pattern and possible explanations for it. We first show that this sex allocation behaviour is indeed consistent across lines from three geographical regions. Second, we test whether females produce sons first in order to synchronize reproductive maturation of her offspring, although our data provide little evidence for this adaptive explanation. Finally we test the age at which females are able to mate successfully and show that females are able to mate and store sperm before adult eclosion. Whilst early-male production may still function in promoting protandry in mealybugs, we discuss whether mechanistic constraints limit how female allocate sex across their lifetime.
[Show abstract][Hide abstract] ABSTRACT: A recent study comparing sex ratios produced by experimental evolution in spider mites with those predicted by Hamilton's Local Mate Competition Theory clearly demonstrates Evolutionary Theory's success as a quantitatively predictive science.
Current biology: CB 12/2011; 21(24):R992-4. · 10.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Local Mate Competition (LMC) theory predicts a female should produce a more female-biased sex ratio if her sons compete with each other for mates. Because it provides quantitative predictions that can be experimentally tested, LMC is a textbook example of the predictive power of evolutionary theory. A limitation of many earlier studies in the field is that the population structure and mating system of the studied species are often estimated only indirectly. Here we use microsatellites to characterize the levels of inbreeding of the bark beetle Xylosandrus germanus, a species where the level of LMC is expected to be high.
For three populations studied, genetic variation for our genetic markers was very low, indicative of an extremely high level of inbreeding (F(IS) = 0.88). There was also strong linkage disequilibrium between microsatellite loci and a very strong genetic differentiation between populations. The data suggest that matings among non-siblings are very rare (3%), although sex ratios from X. germanus in both the field and the laboratory have suggested more matings between non-sibs, and so less intense LMC.
Our results confirm that caution is needed when inferring mating systems from sex ratio data, especially when a lack of biological detail means the use of overly simple forms of the model of interest.
[Show abstract][Hide abstract] ABSTRACT: Mating systems are shaped by a species' ecology, which sets the stage for sexual selection. Males of the gregarious parasitoid wasp Nasonia vitripennis compete to mate virgin females at the natal site, before females disperse. Males could increase their fitness by being larger and monopolizing female emergence sites or by emerging earlier pre-empting access to females. We consider sexual selection on male body size and development time in Nasonia, and a potential trade-off between the two traits. We explored sex-specific patterns of larval and pupal development, finding that smaller wasps developed slower than their host-mates. Using competition experiments between brothers, we found that earlier eclosing males mated more females independently of absolute and relative body size. Our data explain the lack of relationship between fitness and body size in male Nasonia and reinforce the importance of protandry in mating systems where access to mates is time-limited.
Journal of Evolutionary Biology 06/2011; 24(9):2002-13. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Community genetics is a synthesis of community ecology and evolutionary biology. It examines how genetic variation within a species affects interactions among species to change ecological community structure and diversity. The use of community genetics approaches has greatly expanded in recent years and the evidence for ecological effects of genetic diversity is growing. The goal of current community genetics research is to determine the circumstances in which, and the mechanisms by which community genetic effects occur and is the focus of the papers in this special issue. We bring a new group of researchers into the community genetics fold. Using a mixture of empirical research, literature reviews and theoretical development, we introduce novel concepts and methods that we hope will enable us to develop community genetics into the future.
Philosophical Transactions of The Royal Society B Biological Sciences 05/2011; 366(1569):1322-8. · 6.23 Impact Factor