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Why do male terrestrial isopods (Isopoda: Oniscidea) not guard females?
Abstract
Precopulatory mate guarding is a male strategy by which female mates are monopolized and is thought to evolve when female receptivity is temporally restricted (Parker 1974; Grafen & Ridley 1983) thus producing a male-biased operational sex ratio (cf. Clutton-Brock & Vincent 1991; Jormalainen et al. 1994). In many aquatic isopods and amphipods, the female is considered recep-tive only during parturial moult (summarized in Ridley 1983; cf. Table 1), when the marsupium (brood pouch) is developed. In amphipods, sperm is transferred directly into the marsupium to fertilize the simultaneously intro-duced eggs. By contrast, male isopods exhibit internal insemination and transfer sperm into the female oviduct where it meets the eggs when they are released into the marsupium. This reproductive strategy requires the female be in the parturial moult, since it is probably only then that the morphology of the female's genital open-ings makes them accessible to male genitalia (e.g. Ridley 1983). Precopulatory mate guarding has been described in many species of aquatic isopods and amphipods (Table 1), often occurring when female receptivity is restricted. During precopula, both sexes are closely attached to each other and may stay in what is called 'amplexus' for several hours, days, or even weeks. In a recent review, Jormalainen (1998) not only summarized the suggested reasons for, and consequences of, monopolization of females by mate-guarding males, but also stressed the idea of precopulatory mate guarding producing intersexual conflict in these species. Initially, precopulatory mate guarding had been assumed to be simply a cost–benefit decision on the part of the male (Parker 1974). However, there may be energetic costs of precopulatory mate guard-ing in both sexes. In this respect, remarkable differences between species exist, depending on precopulatory behaviour (Table 1). Costs for females may lead to an intersexual conflict over the beginning and the duration of precopula (for summary, see Jormalainen 1998). Thus, females of several species resist the attempts of males to form precopulatory pairs, at least in the early stages of their reproductive cycle (Table 1). Female resistance may in fact be a form of indirect selection for males of higher quality (Ward 1984; Jormalainen et al. 1992; Jormalainen & Merilaita 1993), since only those males are accepted as mates that are strong and/or agile enough to overcome female resistance. If female receptivity is restricted temporally to the parturial intramoult (see above), females will be expected to be temporally monogamous within a single reproduc-tive cycle. However, evidence for multiple mating of females and sperm storage has been presented for several isopod species (cf. Table 1). In sperm-storing terrestrial isopods, for instance, stored spermatozoa remain capable of fertilizing eggs for several months (e.g. Porcellio laevis: Longo et al. 1998) and may be used for successive broods (Heeley 1941; Vandel 1941; Lueken 1962; Johnson 1982). By contrast, sperm is retained for only a couple of weeks, but not over successive broods, in aquatic species (e.g. Thermosphaeroma thermophilum: Jormalainen et al. 1999; but see Veuille 1980, for Jaera albifrons). This difference between aquatic and terrestrial species has important implications for the effectiveness, and thus the evolution-ary stability, of mate guarding. Monopolization of females prior to, or after, insemination is ineffective if the female has already stored active sperm from previous matings. As this is often the case in terrestrial isopods, we may expect mate guarding to have been lost during evolution in terrestrial species owing to the higher costs and unlikely reproductive gain. In terrestrial isopods (Isopoda: Oniscidea), the position of the male on the back of the female during mating strongly resembles the clasping ('amplexus') of marine and freshwater isopods during precopula (e.g. Johnson 1985). However, with the exception of supralittoral species of the genus Ligia (Ligiidae) which represent prototypal oniscid isopods (Schmalfuss 1978, 1989; Carefoot & Taylor 1995) and of one species of the genus Helleria (Tylidae), no hint of precopulatory mate guarding has been presented in Oniscidea thus far (Table 1). Since phylogenetic relatives of Oniscidea, for example Valvifera and 'Flabellifera', as well as prototypal terrestrial species, do guard mates, males of the common ancestor of oniscid isopods, being monophyletic, probably guarded their mates too. A similar evolutionary loss of precopulatory mate guarding is obvious when comparing aquatic and Correspondence: M.
... Previous literature indicates that all the marine isopods including Ligia spp. practice mate guarding (Nicholls 1931;Carefoot 1993;Jormalainen and Shuster 1999;Zimmer 2001;Lopes et al. 2006). The present observations on mate guarding behaviour in the semi-terrestrial species L. dentipes suggest a transitional condition by which mate guarding is retained as in other marine species. ...
... In a way, pre-mate guarding in supralittoral species such as L. dentipes could be considered an ancestral behaviour as all marine species are found to practise this behaviour. Understandably, all terrestrial isopods belonging to the Oniscidea have abandoned the practice of pre-mate guarding in lieu of prolonged sperm storage (Zimmer 2001). As indicated in Table 1, Helleria brevicornis is the only terrestrial isopod that has retained the ancestral behaviour of female mate guarding. ...
... However, the mate guarding duration ranges between 12 and 60 h in L. dentipes, whereas in L. oceanica mate guarding duration extends up to 7 days (Nicholls 1931). During mate guarding, the cost of precopulation is greater for males, because males do not feed at this time and they are more vulnerable to predation (Zimmer 2001). The average duration between parturition and the reproductive moult in T. thermophilum and T. milleri was 6.5 and 15 days, respectively (Jormalainen and Shuster 1999), but about 24 days in L. dentipes. ...
Precopulatory mate guarding is a characteristic feature in the mating behaviour of many Malacostraca, and a necessary prerequisite for those species in which female receptivity for males is restricted to a short period of time after the pubertal/reproductive moult. This study deals with the pre-mate guarding behaviour of the semi-terrestrial isopod Ligia dentipes living in the crevices of coral boulders and rocks in the supralittoral region of the Andaman Islands. As in other isopods, moulting in L. dentipes is biphasic, in which the posterior body part invariably moults first. The guarding male aids the female partner in the removal of the moulted exoskeleton. Mating occurs immediately after the posterior body exuviates. The male leaves the female after copulation and goes in search of another receptive female, demonstrating a polygamous mating system in these isopods. The mated females also re-mate with several other males without mate guarding. Females that had mated several times produced more young, compared to females mated only once in the laboratory. Female receptivity ceases following moulting of the anterior half. Intrasexual encounters among males lead to the large males acquiring receptive females. This study reveals interesting deviations from the general pattern of mate guarding already reported in other isopods and decapods. The evolutionary and ecological significances of mate guarding, intrasexual and intersexual conflicts, found in these semi-terrestrial isopods, are discussed.
... However, Zimmer (2001 noted that mate guarding generally does not occur in terrestrial crustacean species. Mate guarding could have been lost in this group because the cost of this strategy would be higher than the reproductive gain, following the evolution of mating systems during adaptation to the terrestrial environment (Zimmer 2001). For example, the evolution of sperm storage in terrestrial isopod females, following the appearance of internal fertilization, would have meant that a mate-guarding male could not ensure his exclusive paternity (Zimmer 2001). ...
... Mate guarding could have been lost in this group because the cost of this strategy would be higher than the reproductive gain, following the evolution of mating systems during adaptation to the terrestrial environment (Zimmer 2001). For example, the evolution of sperm storage in terrestrial isopod females, following the appearance of internal fertilization, would have meant that a mate-guarding male could not ensure his exclusive paternity (Zimmer 2001). The loss of mate guarding would therefore have allowed the evolution of multiple mating in terrestrial crustaceans. ...
... Multiple mating has been documented in land isopods (Oniscidea, woodlice;Lueken 1963;Johnson 1976;Sassaman 1978), and sperm stored after a single mating remains functional over many clutches (Schobl 1880;Lueken 1963;Adamkewicz 1969;Johnson 1976). Zimmer (2001) did not propose an alternative strategy for males to increase their probability of paternity in terrestrial crustaceans, but many strategies have been selected in other terrestrial arthropods, for example, the reduction of postmating receptivity in females (Eberhard 1996;Simmons & Siva-Jothy 1998). A better knowledge of female remating in terrestrial species would therefore help us to understand how mating strategies evolved in crustaceans. ...
In most species, both sexes may mate with more than one partner during their life. In terrestrial isopods (woodlice) female remating can occur within a reproductive season (immediate remating) or after a period of sexual rest and sperm storage, that is in a subsequent reproductive season (delayed remating). The pattern of sperm precedence is unknown in both cases. These two female remating patterns may shape male–male competition in different ways. To elucidate both patterns of female remating and sperm precedence, we used an albinism mutation in Armadillidium vulgare to track paternity in laboratory experiments. Males had low remating success after immediate remating attempts, mainly because of the female's refractory behaviour. However, refractory behaviour seemed to be lost after female sexual rest: delayed remating attempts were as successful as first mating attempts with virgin females. In both immediate and delayed remating, competing males had similar fertilization success, but varied in sperm precedence. We hypothesize that males might induce the refractory mating behaviour in females to ensure their paternity. This could be a strategy that evolved in woodlice after the loss of precopulatory mate guarding during adaptation to the terrestrial environment. We discuss the consequences of these findings for woodlice optimal mating strategies. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
... In crustaceans, the morphological structures to store spermatozoa/spermatophores are highly diverse, and their homologies in many cases are not clear, especially within the nonmalacostracans. Paired or unpaired sperm/spermatophore storage chambers are found in Anostraca (Martin 1992), Cirripedia (Walker 1992), Copepoda (Boxshall 1992, Corni et al. 2000, Titelman et al. 2007), Branchiura , Ostracoda (Cohen andMorin 1990, Matzke-Karasz et al. 2009), Isopoda (Wilson 1991, Johnson et al. 2001, Zimmer 2001, Suzuki and Ziegler 2005, Ziegler and Suzuki 2011, Euphausida (Guglielmo and Costanzo 1983), and Decapoda (Table 15.1) (for review, see Adiyodi and Subramoniam 1983, Bauer 1986, Wortham-Neal 2002, Sainte-Marie 2007. In many cases, the sperm/spermatophore storage chambers are differentiated regions of the genital duct, and in other cases they are morphologically separated from the genital duct. ...
... While most crustacean taxa feature one or maximally two different types of seminal receptacles, all four "designs" can be found among the Isopoda. The morphological diversity of the reproductive tract and its impact on mating strategies have been related to the aquatic or terrestrial habitat of the diverse taxa of isopods (Zimmer 2001). Thus, isopods appear an excellent model to study phylogenetic trends in sperm storage and the influence of the habitat on the coevolution of form-function and reproductive behavior. ...
This chapter brief ly describes the diversity in the functional morphology of the crustacean reproductive organs from both macroscopic and microscopic approaches. The anatomical design of the female reproductive system involving the different positions of germaria and growing oocytes and types of accessory cells is compared within crustaceans and partially with other Arthropoda. Male reproductive systems also show diversity in testes design and in the proposed roles of Sertoli-like cells. The genital ducts in both females and males show large morphological variability related to their functions in gamete transport, sperm matura-tion, sperm storage, and spermatozoa packaging. This anatomical diversity is proposed to be partially driven by the environment since some similar morphofunctional patterns are found in similar habitats. Specially, different patterns of sperm storage are discussed within the framework of sperm competition. Reproductive morphology in hermaphroditic and intersex species is also included and compared, highlighting the significance of these reproductive models to understand sexual differentiation mechanisms in crustaceans. Finally, morphological comparative studies are proposed to address questions related to the evolution of general and particular designs and primitive and advanced patterns, as well as the study of the embryological development of the reproductive system as a key to understand the differences between and within taxa and neurohormonal pathways of sexual differentiation and endo-crine disruption.
... Precopulatory mate guarding in male terrestrial isopods, however, is rare, although males may adopt a posture resembling amplexus during internal fertilization of females. Zimmer ( 2001 ) notes that aquatic isopod females generally do not store sperm between matings (Jormalainen et al., 1999 ), whereas terrestrial isopod females can store sperm for several months ( P. scaber , Longo et al., 1998 ) and over several broods ( A. vulgare , Lueken, 1962;Venezillo evergladensis , Johnson, 1982 ). Hence male mate-guarding behavior in terrestrial isopods would be an ineff ective strategy if a female has already mated with a previous male. ...
... A rare oniscid exception is the genus Ligia , in which males exhibit precopulatory mate guarding (Schmalfuss, 1989 ;Carefoot and Taylor, 1995 ). Th e Ligiidae are supralittoral and appear to be prototypal oniscids, suggesting that precopulatory mate guarding was lost early as the Oniscidea evolved in terrestrial environments (Zimmer, 2001 ). Mead ( 1973 ) described the courtship behavior of A. vulgare , in which a courting male assesses a female with his antennae and thereafter attempts to mount her dorsal surface. ...
Terrestrial isopods (Crustacea: Oniscidea) are important detritivores in many ecosystems. Because reproductive success and population dynamics of the Oniscidea depend on diverse biotic and abiotic environmental factors, the effects of global climate change on their biology may be significant. Although few studies have examined the relationship between climate change and population ecology in terrestrial isopods, much is known about their environment, genetics, physiology, behavior, life history, population biology, and evolutionary patterns. This review addresses the influence of biotic and abiotic environmental factors on terrestrial isopod reproduction. Significant biotic factors include microorganism-mediated sex determination, mate choice, sperm competition, maternal effects, food availability, and predation. Significant abiotic factors include temperature and moisture regimes, photoperiod, altitude, latitude, and microhabitat diversity. Studies of these factors reveal general patterns, as well as informative exceptions, in the ways different oniscid species, as well as different populations within a species, respond to environmental variation.
... It appears that neotenic forms have evolved independently over a number of times. This phenomenon is associated with a change in sexual systems where mate guarding is probably not as important in the terrestrial environment as it is in the aquatic (see also Zimmer 2001). The energetic demands of carrying large gnathopods can be compensated, and the neotenic condition becomes more appropriate. ...
This volume examines Evolution and Biogeography of Crustacea, one of the dominant groups of animals, especially in aquatic environments. The first part of this volume is dedicated to the explanation of the origins and successful establishment of the Crustacea in the oceans. In the second part the biogeography of the Crustacea is explored in order to infer how they conquered different biomes globally, while adapting to a wide range of aquatic and terrestrial conditions. A final section examines more general patterns and processes, and looks to the future. Collectively, these eighteen chapters provide a thorough exposition of present knowledge across the major themes in evolution and biogeography of crustaceans. They do this by summarizing what is known and providing novel analyses of patterns.
... In most terrestrial oniscidean isopods, males do not guard females (but see Linsenmair 1989 and A in Fig. 12.1). Within Oniscidea, sperm storage organs have evolved and female receptivity is no longer time-limited (Zimmer 2001). Specialized structures for sperm storage, referred to as either seminal receptacles or spermathecae, have also evolved in janiroidean Asellota and Sphaeromatidea, and those show a high degree of structural diversity (Wilson 1991, Longo et al. 1998. ...
This is the sixth volume of a ten-volume series on The Natural History of the Crustacea. The volume synthesizes in nineteen chapters our current understanding of diverse topics in crustacean reproductive biology. The first part of the volume address allocation strategies to reproduction, gamete production, brooding behavior and other components of parental care in crustaceans. The second part of the volume centers on sexual systems in crustaceans. The third section of the volume covers crustacean mating systems and sexual selection. The volume ends with three chapters covering diverse topics including reproductive rhythms, and crustacean personality research, and record breaking crustaceans with respect to reproductive characters. Collectively, these nineteen chapters provide an integrative and comprehensive treatment of crustacean reproductive biology from gamete formation to mating and reproductive strategies and their evolutionary and ecological consequences.
... In most isopods, a true copula occurs and males inject sperm in the female spermatheca (Wilson 1991). Females can store sperm for long periods (~months) and fertilization is thought to be internal during oviposition (Zimmer 2001). Multiple paternity of clutches has been documented in amphipods and isopods, and is also likely for other peracarids (Birkhead andPringle 1986, Dennenmoser and. ...
Many crustacean species are known to provide parental care, with behaviors ranging from ventilating the eggs to providing food for young. This chapter provides an overview of parental care patterns across crustaceans, and then compares crustacean parental care to that of select other taxa (insects, fishes, frogs) that share important traits with crustaceans (exoskeleton, aquatic or amphibious lifestyle, respectively). The aim is to identify gaps in the understanding of the evolution of parental care in crustaceans. We show that nearly all crustaceans provide parental care for early embryos (eggs), while caring for advanced stages is rarer. The most common forms of care are simple behaviors (e.g. fanning and cleaning behaviors), while complex behaviors (e.g. feeding the young) evolved exclusively in groups that also care for longer. Caring is most frequently done by
females, while biparental is rare, and exclusive paternal care is nonexistent. When compared across taxa, simple behaviors are also the most common forms of care, and reasons for the evolution of parental care have common themes. First, parental care enhances offspring survival. In crustaceans, early embryo/ egg mortality is apparently high, which might have triggered the evolution of parental care in several crustacean taxa independently. Second, crustaceans that have large eggs and inhabit stable habitats tend to care for longer. Lastly, internal fertilization seems to prevent male crustaceans from caring by not allowing the males to access the eggs and to ensure paternity.
... However, females of other species can also store the sperm (e.g., copepods Calanus spp., Eurytemora affinis; Marshall andOrr 1955, Katona 1975, respectively) or mate every reproductive cycle (e.g., copepods Acartia tonsa, Temora stylifera; Wilson andParrish 1971, Ianora et al. 1989, respectively) and do not seem to have any sort of postcopulatory mate guarding. For example, oniscid isopods have lost the precopulatory amplexus, probably in the course of their evolutionary shift from an aquatic to a terrestrial lifestyle (reviewed in Zimmer 2001). A possible explanation could be that oniscid females can store sperm, such as in Porcellio, Venezillo, and Armadillidium. ...
Due to an exceptional variety of habitats, body plans, and lifestyles, crustaceans exhibit a wide array of mating systems. Some groups engage in simple, pure- search polygamous systems in which males usually search for receptive females. In other groups, males defend valuable resources to attract and/ or guard females to ensure paternity. Some species have developed highly complex systems of harem defense polygyny and monogamy, even cases of sub- and eusociality are reported. The expression of mating systems does not seem to be uniformly correlated to taxonomic affiliation, but is
rather diverse within certain groups, suggesting that the evolution of mating systems is largely facilitated by the lifestyle of the species. Despite the broad range of mating systems in crustaceans, and although some groups have been studied comparably well, there remains a lack of knowledge about the behavioral and sexual biology of many species. In the light of the high diversity of lifestyles, mating systems, and habitats of certain groups, crustacean species would be ideal models to unravel the evolution of reproductive strategies and social behaviors.
... Breeding events occur for both males and females of this iteroparous species throughout their entire reproductive lifespan during up to four years (see Lawlor, 1976;Stearns, 1989;Dangerfield and Hassal, 1992;Caubet, 1998), including one or more broods within a season (Hornung, 2011). In terrestrial isopods, the existence of sperm storage organs, in the spermathecae, allow females to keep the sperm of previous copulations in their genital tracts and to use the sperm months, or even years, later to fertilize their oocytes (see Zimmer, 2001, for a review). In natural populations, reproductive animals thus belong to different cohorts (i.e., more or less synchronously born broods), and the largest animals can be nearly ten times of the size of the smallest sexually mature ones (Brody et al., 1983). ...
In the terrestrial crustacean Armadillidium vulgare, a large size range exists in natural populations within which males and females could potentially mate. Because of continuous growth far beyond sexual maturity, the largest individuals can be nearly ten times the live mass of the smallest sexually mature individuals. In this study, we explored the influence of male and female body mass on the mating behaviour and success. Starting with a representative panel of males and females in which females are significantly larger than males in average, we followed the sexual behaviour of 23 groups of 20 mixed-sex virgin animals under conditions comparable with natural field situation during the early breeding season. We found a correlation between paired individuals showing an assortative pairing. During pairing male stimulates female and duration of stimulation is determinant for pairing follow-up: efficient stimulation is correlated with female size and not with male size. In consequence, pairs in mating show a reversed size dimorphism between male and female where female are about 20% smaller. Largest females were not mated. During copulation behaviour, the quantity of sperm transferred is positively correlated with copulation duration. Stored sperm can be used for immediate breeding by the female and stored in the spermatheca for future breeding. The last option allows to largest females in the field to continue breeding without additional mating, avoiding the lack of availability of large males able to stimulate them efficiently.
... These details would require development in order to model exploration of different environments, saturation of shelters, and detailed mechanisms to maintain aggregates. Further development of the model would also be required to simulate the spatial distribution of woodlice in nature, including attraction to food sources [29], life-cycle and gender [30], and interactions with other species and the environment [31]. This could be of broad interest, as the study of woodlice aggregation is relevant to a number of areas, including soil dynamics [32], bioindication [33], terrestrialisation and social adaptation [9,34] Czaczkes et al. [35] recently developed an agent-based model of ant foraging in which individuals specialise in exploiting different resource sites based on their experience of the environment and memory. ...
Aggregation of many species of invertebrate is an example of a consensus decision, the success of which is central to survival. Personality is a stable form of behavioural diversity which has been observed in the aggregation process, but neither the reasons for its stability nor its effects on consensus decisions are well understood. By using an agent-based model of invertebrate aggregation, it is found that diverse personalities have only limited benefits to the experimental consensus decision-making process, but may have a more valuable role in natural settings. Importantly, although certain personalities may ostensibly have potential drawbacks at the individual level, such as choosing to rest in unfavourable places, all individuals are likely to benefit from maintaining a constant personality, which promotes group stability. These findings help to improve understanding of consensus decision-making and the prevalence of stable personality.
... It is likely that stridulation of male C. japonica functions as a form of threatening competitive male intruders or predators at the entrance of the narrow nesting cavity. Zimmer (2001) suggested that male precopulatory guarding in isopods has disappeared as a consequence of the evolutionary loss of the temporal-restricted female receptivity cycle, which was limited by cycle(s) of parturial molting during adaptation from aquatic to terrestrial habitats. At least, in the case of A. officinalis, it would be difficult physically to produce sound while guarding a female beneath them (ventral side). ...
A vast variety of acoustic behaviors and mechanisms occur in arthropods. Sound production, in particular, in insects and decapod crustaceans has been well documented. However, except for a brief, anecdotal statement, there has been no report on the acoustic behavior of aquatic isopods. We present the first empirical evidence in aquatic Isopoda that males of Cymodoce japonica produce sound by stridulation, or the rubbing together of body parts. Sound production was associated with tail-lifting behavior, suggesting that stridulation occurs on thoracic and or abdominal somites. Acoustic analysis revealed that syllable length was similar throughout the stridulation, at a mode of 25003000 Hz. With a scanning electron microscope, we identified file-like structures on the inner surface of the dorsal exoskeleton. Each file consisted of 188 ± 11.1 ridges at about 0.5 µm intervals; the theoretical frequency (number of ridges per syllable length) was estimated to be 2208-3646 Hz. This finding suggests that the stridulation sounds arose from these structures. Laboratory observations show that stridulation may play a role in the threatening of other males in the context of territorial and or reproductive competitions.
... Multiple mating is a prerequisite for cryptic female choice to evolve and is commonly found in animals (e.g., Jennions and Petrie 2000;Simmons 2005). In crustaceans, a plethora of studies has accumulated evidence for multiple mating over the past decades (e.g., Sassaman 1978;Johnson 1982;Christy and Salmon 1984;Shuster 1989a;Bauer 1996;González-Gurriarán et al. 1998;MacDiarmid and Butler 1999;Franke 2000;Hartnoll 2000;Clark and Caudill 2001;Zimmer 2001;Moreau et al. 2002;Jensen and Bentzen 2012;Bailie et al. 2014). Most studies rely on direct behavioral observations, but multiple matings do not necessarily translate into multiple paternity or biased offspring ratios (Eberhard 1996). ...
Cryptic female choice
may be common among crustaceans
, but few studies have thoroughly examined it in this diverse taxonomic group. Herein, we summarize current genetic evidence for multiple paternity
and skewed offspring ratios in crustaceans, and document observations that could suggest cryptic female choice. Behaviors indicative of cryptic female choice have been reported from numerous crustacean taxa (e.g., crayfish
, hermit crabs
, isopods
), showcasing a diverse array of behavioral mechanisms such as failed copulations, spermatophore removal
, selective sperm passage, chemical signaling
, adjusting duration of receptivity, delayed copulation
, or discriminative reproductive investment in favor of preferred males. We highlight a few case studies, in which a suite of different cryptic behaviors permits females to maintain control over fertilizations. The possibility of selective sperm–egg interactions
is briefly discussed, and parallels to other aquatic invertebrates are drawn revealing similar cryptic choice mechanisms. The disparity of body forms and reproductive strategies found in crustaceans
and the fact that they inhabit many different habitats with variable selective environments makes them an ideal model taxon for future studies on cryptic female choice
.
... Despite these advantages and an extensive literature on many aspects of the biology of isopods (e.g., Sutton & Holdich, 1984;Ferrara et al., 1989;Warburg, 1993;Alikhan, 1995;Hassall et al., 1998), including the behavioral and physiological changes accompanying terrestriality (e.g., Edney, 1968;Cloudsley-Thompson, 1977;Wieser, 1984;Warburg, 1987Warburg, , 1993Carefoot, 1993;Wright & Machin, 1993;Greenaway & Warburg, 1998;Zimmer, 2001), no one has made a concerted attempt to compare the ecology and life histories of aquatic and terrestrial species using the same methods. Extensive data on life histories of both aquatic and terrestrial isopods already exist, but the methods and kinds of data collected have usually been so different or otherwise insufficient that useful marine-freshwater-terrestrial comparisons cannot be made at present. ...
... In such a situation, males may engage in behaviours that reduce this risk, such as guarding receptive females. Given long-term sperm storage and continuous female receptivity in symbiotic janirids, even prolonged guarding of large females may not lead to a substantial reduction in the risk of sperm competition (see also Zimmer 2001). Furthermore, a study by Johnson (1982) indicates that in isopods, first males' sperm have a fertilisation advantage. ...
Mating systems of many symbiotic crustaceans are characterised by a high degree of mate guarding. A peculiar case of mate guarding has been reported for small symbiotic janirid isopods where males mate with immature females. Field samples of individual hosts and laboratory experiments were conducted to reveal the mating behaviour of the symbiont in a natural environment, that is, on their hosts. Along the coast of the Magellan Strait, Chile, the janirid isopod Iais pubescens was frequently found on the shore-living isopod Exosphaeroma gigas. Symbiont prevalence (percent hosts occupied) was high at eight of the nine sampling sites. Mean symbiont intensity was very low at one site (<<1 individual host-1), intermediate at two sites (1-10 individuals host-1) and high at the other sites (10-40 individuals host-1). The mean sex ratio (males:females) was male biased at most sampling sites (n=7). Females of I. pubescens reached substantially larger sizes (1.5-3.0 mm body length, BL) than males (1.1-1.9 mm BL). The majority of males were carrying small juveniles (66.15%), and males with juveniles were significantly larger than males without juveniles - this suggests that males prefer virgin juveniles to adult females and that they compete for small juveniles. In laboratory observations, males were seen to manipulate the marsupium of adult females that were about to release small juveniles. Males obtained virgin juveniles in this manner. Juveniles were carried for ~7 days, and they moulted shortly before being fertilised and released by males. The high proportion of juveniles carried by males in the field (68.2%) supports previous observations that males initially are not able to distinguish male and female juveniles. It is suggested that the mating system of symbiotic janirid isopods with long-term sperm storage and continuous receptivity in females and male mating with virgin females has evolved in response to highly unpredictable encounter probabilities between the sexes. Mate guarding and manipulation of small virgin juveniles may be favoured on the highly mobile hosts of symbiotic janirid isopods. Furthermore, adult females may gain by leaving their emerging offspring in the protective grip of guarding males, thereby reinforcing the maintenance of this peculiar mating system.
... The potential for cryptic female choice in crustaceans In many crustacean species, females mate with multiple males (e.g. Christy and Salmon 1984;Koga et al. 1993;Bauer 1996;Gonzµlez-Gurriarµn et al. 1998;MacDiarmid and Butler 1999;Franke 2000;Hartnoll 2000;Clark and Caudill 2001;Zimmer 2001), and these males may vary substantially in important characters such as size, age, resource holding power, or physiological capacity. Some of the best-documented cases are crabs from the genus Chionoecetes, where females mate multiply with males of different ages and sizes Paul 1992, 1996;Urbani et al. 1998). ...
While studies on a wide diversity of organisms have demonstrated the importance of female behavior during matings, in crustacean studies, a strong bias towards male mating behavior prevails. Reproductively mature rock shrimp (Rhynchocinetes typus) exist as several ontogenetic stages that differ in their morphological and physiological capacities. In natural populations, the majority of males are in early ontogenetic stages (termed typus), many are in intermediate stages (intermedius), and few are in the terminal molt stage (robustus). Dominant robustus males, which have already demonstrated their biological fitness by surviving to this stage, have previously been shown to have a higher potential than subordinate typus males to defend receptive females against other males, and fertilize the entire clutch of a female. While females should thus show a preference for robustus males, they nevertheless frequently receive sperm from typus males. These observations suggested that females might have mechanisms to discriminate against sperm from subordinate males. In laboratory experiments, we observed that females avoided being seized by typus males for longer time periods in the absence of robustus males than in their presence. Following seizure, females that were initially held by typus males, required more time to initiate spawning than those held by robustus males. Many typus males transferred spermatophores to females before these started to spawn while robustus males waited until females began to spawn before they transferred spermatophores. Females manipulated spermatophores received from typus males for long time periods (minutes), but not those they received from robustus males. By accepting sperm from subordinate typus males, females may avoid further harassment (convenience polyandry), but they subsequently may discriminate against these subordinate males by delaying spawning and removing their sperm. These observations suggest that female behavior influences the outcome of matings, favoring fertilization of eggs by sperm from dominant males. Convenience polyandry and cryptic female choice may be common in other crustaceans as well.
Isopods show a wide range in mating systems. Mate guarding by males before copulation occurs commonly in most free-living taxa, with the notable exception of the terrestrial Oniscidea. Such guarding prior to copulation is interpreted as a male mate monopolization strategy, evolved as a response to short female receptivity to copulation. Males are able to assess female maturity and to adjust guarding duration accordingly; relatively long guarding duration is often optimal for males. Guarding has no known benefits for females. Moreover, guarding is likely to impose costs for females, thus leading to a sexual conflict. Experimental studies suggest that conflicts over the start of guarding generate sexual selection for traits related to obtaining or resisting mates, as well as for traits related to cryptic female choice. Isopod mating systems can be used to clarify the roles played by traditional female choice and intersexual conflicts in sexual selection.
A key feature of crustaceans important in their social and sexual evolution is the presence of supernumerary appendages that are modified for a variety of functions. Claws are employed in agonistic and courtship interactions, underlining their importance in the evolution of social behavior. Other appendages carry diverse chemosensory structures, allowing crustaceans to obtain information about their environment, including the presence, status, and even individual identity of conspecifics. Most crustaceans are aquatic and, as a group, crustaceans are best adapted to this environment. Most large decapods release planktonic larvae, but many smaller and terrestrial crustaceans release fully developed offspring. The mode of dispersal influences the structure of kin groups and populations, and the behavioral constraints and opportunities that arise therefrom. Besides such organismal characteristics, extrinsic factors such as resource availability and predation have figured in the evolution of social and sexual systems in crustaceans. Present knowledge of their social behavior is approaching levels that permit rigorous comparisons across taxa, making crustaceans a valuable model system for the study of social and sexual evolution.
This chapter briefly describes the diversity in the functional morphology of the crustacean reproductive organs from both macroscopic and microscopic approaches. The genital ducts in both females and males show large morphological variability. This anatomical diversity is proposed to be partially driven by the environment since some similar morphofunctional patterns are found in similar habitats. Specially, different patterns of sperm storage are discussed within the framework of sperm competition. Reproductive morphology in hermaphroditic and intersex species is also included and compared, highlighting the significance of these reproductive models. Finally, morphological comparative studies are proposed to address questions related to the evolution of general and particular designs and primitive and advanced patterns, as well as the study of the embryological development of the reproductive system as a key to understand the differences between and within taxa and neurohormonal pathways of sexual differentiation and endocrine disruption.
Light and electron microscopic studies that we have published in the past have reported many aspects of the reproductive process in Armadillidium vulgare with particular emphasis on the reconstruction of female genitalia. Together this body of work provides an almost complete, albeit fragmented picture of these processes and include many data on sperm storage and sperm translocation. Females of A. vulgare have a pair of cuticular genitalia in the lumen of the oviduct. For insemination, these genitalia can receive the copulatory organs of males formed by the elongated tips of the first two pleon endopods. During transitions between reproductive (parturial) and non-reproductive (normal, non-parturial) moult cycles the genitalia undergo intriguing structural changes resulting in two types of genitalia. Throughout their reproductive lifetime, either type is reconstructed after each moult depending on the reproductive phase of the female. In this review, we integrate the events that occur during a reproductive cycle with particular emphasis on the genitalia reconstruction and sperm storage, and discuss functional aspects of the genitalia. Thereby, we provide a case model that can be useful for further studies on genitalia diversity and female reproductive strategies in terrestrial isopods.
Due to their world-wide distribution in marine and terrestrial (as well as freshwater)
habitats, the order Isopoda (Crustacea: Malacostraca: Peracarida) provides an excellent model for
the evolutionary ecology of terrestrialization.
(1) Terrestrial isopods (Oniscidea) harbor endosymbiotic bacteria in their midgut glands (hepatopancreas)
that are lacking in marine isopods of the suborders Valvifera and Sphaeromatidea, considered
being (part of) a sister taxon of Oniscidea. Thus, these bacterial endosymbionts seem to be
significant in the context of living in terrestrial habitats and may have been important during the
course of terrestrialization. In truly terrestrial species (Crinocheta), two different endosymbionts
have been characterized that are distantly related to known parasites and pathogens of the orders
Rickettsiales and Mycoplasmatales, respectively. Both these endosymbionts form cytoplasmic appendages
that are in contact with the host epithelium and may serve in the exchange of nutrients
and information and or serve as holdfasts. In non-crinochete terrestrial isopods (Diplocheta, Tylida,
Synocheta), hepatopancreatic bacteria belong to the genus Pseudomonas.
Both marine and freshwater Asellota also harbor bacteria in their midgut glands. The lack of bacteria
in other marine suborders (as studied so far) may be due to antibiotic agents in these isopods.
Based on the present findings, I propose a common (marine) ancestor of Asellota and Oniscidea
that acquired the ability to harbor bacterial endosymbionts inside the hepatopancreas. While symbiotic
relationships remained unspecific in marine Asellota, they developed towards specific primary
symbioses with bacteria that aid in digesting cellulosic and phenolic compounds, and thus, facilitate
the utilization of terrestrial food sources in semi-terrestrial and terrestrial Oniscidea and in
freshwater Asellota. I, further, hypothesize that later during early phylogeny of Crinocheta, primary
symbionts have been replaced by secondary endosymbionts that are still characteristic of recent
Crinocheta.
In contrast to previous studies, suggesting a role of hepatopancreatic bacteria in nutrition, our present
knowledge does not provide any evidence for crinochete symbionts to supply any digestive enzymes
to their isopod host. However, Pseudomonas spp. are well-known to degrade both cellulosic and phenolic
compounds. Thus, I hypothesize that, while primary symbionts of Oniscidea provide cellulases
and/or phenol oxidase, a transfer of cellulase and/or phenol oxidase genes from symbiont to host
occurred in early Crinocheta, resulting in endogenous cellulase of evolutionarily bacterial origin. Besides
(a) providing enzymes for the digestion of leaf litter, further possible contributions of hepatopancreatic
endosymbionts to their hosts physiological constitution and fitness include (b) increasing
the availability of nitrogen on a nitrogen-poor food source, (c) protecting their host from secondary
(pathogenic) infection, (d) protecting their host from predatory attack, or (e) increasing fertility, mating
success and fecundity of their host these hypotheses are briefly discussed.
(2) Terrestrial isopods interact with leaf litter-colonizing microbiota that they ingest along with their
major food source. While, however, it is well-documented that isopods gain from feeding on microbially
inoculated leaf litter, reasons for this dependence are not well understood. Possibly, (a) microbiota
serve as supplementary high-quality food source and provide essential or otherwise limiting
nutrients; (b) microbiota promote digestion of leaf litter itself, either prior to ingestion or during the
gut passage; (c) microbiota simply act as indicators of easily digestible food sources of high quality.
These explanations are not mutually exclusive, and the prevailing reason for preferentially consuming
microbially inoculated leaf litter depends on both the species and developmental stage of the isopod
and the nutritional context, i.e. the food source as such; recent results, however, indicate that cellulolytic
capabilities of litter-colonizing microbiota [see (b)] may be less significant than previously
thought, while a role of litter-colonizing microbiota in indicating high-quality food [see (c)] is supported.
The ability to digestively utilize microbial cells as supplementary food [see (a)] depends on cell
wall characteristics as indicated by gram-staining of the microbes, gram-positive bacteria being
digested more effectively than gram-negative bacteria and fungi, and being preferred as food source.
Despite numerous studies, the most recent ones using modern molecular techniques, it is still debated
whether or not terrestrial isopods harbor resident gut microbes in their hindgut. Most hindgut
bacteria that may be candidates for hindgut residents appear to belong to gram-negative bacterial
taxa, and are taxonomically related to anaerobic species. Thus, we have to assume anoxic
microhabitats in cuticular wrinkles. Further, the radial center of the hindgut is anoxic, too, allowing
for fermentative digestive processes, while the periphery of the hindgut lumen is largely oxic and
oxidizing, thus, allowing for aerobic and oxidative digestive processes. These processes are promoted
through cell compounds of ingested microbiota resulting in homeostatic maintenance of a
slightly acidic pH that is optimal for the activity of involved enzymes. Potentially harmful effects of
phenolic food compounds that are likely under such conditions are counteracted through hydrolytic
enzymes and surfactants of microbial origin.
In conclusion, our up-to-date knowledge as summarized and discussed herein strongly confirms
the assumption that (terrestrial) isopods strongly depend on microbial activity and nutrients for
their capability of digestively utilizing terrestrial leaf litter; on an evolutionary scale, this dependence
may indicate the role that microbiota played during the course of terrestrialization, although
this aspect of isopod-microbe interactions is far from being understood.
The reproductive cycle of female Tylos granuliferus was investigated in laboratory conditions. We focused our experiments on female copulative timing for effective insemination and on female sexual receptivity for reproduction. We used females who were isolated from males along with delayed copulation. The female reproductive cycle of T. granuliferus is related to the parturial moult cycle. Females copulate soon after shedding the posterior half of their body cuticle through anterior shedding with a shedding interval of 2 days. Copulation ends just before oviposition. The optimum timing for copulation is within a few days after completion of the parturial moult. Oviposition immediately follows insemination. Without copulation, females do not oviposit their eggs. Pre-copulatory mate guarding by males and sperm storage by females for future broods do not appear to occur in this species. Isolated females have a sexual receptive period of 12 days during the early stages of the reproductive cycle and cannot produce mancas if insemination is more than 10 days later after the parturial moult. We propose that females are exposed to oviposition-stimulating factors at copulation to oviposit the fertilized eggs into their marsupium.
Mate choice is mediated by many components with the criteria varying across the animal kingdom. Chemical cues used for mate attractiveness can also reflect mate quality. Regarding the gregarious species (isopod crustacean), we tested whether individuals can discriminate conspecifics at two different levels (between sex and physiological status) based on olfactory perception. Tested conspecifics were individuals of the same or opposite sex, with the females at different moult stages. We found that the attractiveness of individuals was mediated by short-distance chemical cues and tested individuals were able to discriminate and prefer individuals of the opposite sex. Moreover, male preference to female increased during their moulting status as they matured. Males were particularly more attracted by females with appearing white calcium plates, which corresponds to the beginning of their higher receptivity period. These differences in attractiveness due to sex and physiological status are likely to shape the composition of aggregates and facilitate mate finding and optimize the reproductive success for both males and females. Thus aggregation pheromones could be linked to sex pheromones in terrestrial isopods.
Isopods are the only crustacean taxon with many truly terrestrial species, including desert inhabitants. These species show a highly developed social behavior that is crucial for survival under the harsh conditions in desert environments. The desert-living Hemilepistus spp. depend on burrows that are costly to produce, can only be dug anew in spring, and have to be continuously defended against competitors. This is achieved by division of labor between the sexually and socially monogamous pair partners, and later with the progeny's participation. Using a comparative approach, this chapter draws inferences about the probable evolutionary route to the strict monogamous mating system found in one of the best studied and highly social species, H. reaumuri. It concludes that the narrow temporal window during which the extremely valuable family burrow can be constructed has resulted in the sophisticated social behavior found in this semelparous oniscoid isopod.
The cuticular genitalia of the terrestrial isopod, Armadillidium vulgare, have two distinct states during the reproductive cycle of the females. The structural differences between the reproductive and non-reproductive states, and the structure of the sperm storage sites were investigated employing electron and light microscopy. In both states the genitalia consist of a distal segment that connects to the gonopore, and a cuticular tube-like structure lining the lumen of the oviduct in the middle region of the oviduct. Sheath-like projections, apparently consisting of cuticular material, extend laterally along two sides of the cuticular tube. In the proximal region of the oviduct cuticular structures are lacking. In the non-reproductive state the distal segment consists of endo-, exo- and epicuticle. The exocuticle is three layered with unusual spongy and dense layers at the distal side. On one side the endocuticle doubles in thickness to form a cuticular bulge that fills the lumen of the distal segment leaving just a narrow U-shaped space. The cuticular tube consists of endo- and epicuticle only. In the reproductive state the distal segment is funnel-shaped and forms branched cuticular folds that increase in complexity from distal to proximal. In the cuticular tube these folds tightly fill the lumen of the oviduct. At the confluence of the oviduct with the ovary spermatozoa are stored in a seminal receptacle.
Successful invasion must be viewed as the result of a unique sequence of events, with the established species overcoming a number of previously prohibitive obstacles, for example lack of dispersal vectors, habitat characteristics and environmental conditions of the new area, and the ability to persist in interspecific interactions in the new community. The Japanese skeleton shrimp, Caprella mutica, is proving to be a highly successful non-native crustacean in coastal waters outside its native range having overcome these obstacles. In the past 40 years, C. mutica has spread from its native sub-boreal waters of north-east Asia to numerous locations in both the northern and southern hemisphere, where it has successfully established self-sustaining and thriving populations. After its first European record from the Netherlands in 1995, C. mutica spread rapidly within the North Sea and later to the west coast of Scotland and to Ireland in less than 15 years. Caprella mutica is generally associated with man-made structures and can be found in abundance on boat hulls, floating pontoons and aquaculture infrastructure clinging to fouling organisms.
In Gammarus pulex, male–male competition is generally intense because the operational sex ratio (OSR) is strongly biased towards males; however, studies have shown possible fluctuation in this intrasexual competition, which could be caused by sperm depletion, a phenomenon recently found in gammarids. Sperm depletion may also affect male mating behaviour. We therefore tested the influence of sperm depletion on the OSR in G. pulex. Two sets of experiments were conducted: first, to find out the number of sperm in the testis before and after mating events (sperm depletion), and second, to test the implications of sperm depletion for the mating behaviour of male G. pulex.We found substantial sperm allocation to each reproductive event but also a relatively fast replenishment. However, contrary to one of our hypotheses, sperm depletion had no impact on the male reproductive ‘time-out’ and therefore on the OSR, since depleted males could engage in a precopula within a few hours of a previous copulation. The decision to initiate an amplexus de novo was more dependent on indicators of the female's quality such as her time left to moult. Depletion status also did not affect male competitive ability. Indeed, in a competitive context, recently mated G. pulex males were more likely to pair again than those males that had not mated recently, independently of sperm reserves, male size and energy storage. Consequently, some males had better access to reproduction than others, which could be explained by various hypotheses.
In the terrestrial crustacean At madillidium vulgare the prolonged presence of males along with females is known to boost female reproductive physiology, and the so-called 'male-effect' was best characterized by a significant shortening of the pre-parturial intermoult (PPI) during which oocyte maturation spontaneously takes place Continuous presence of a male over that period can speed up both the vitellogenesis and the moulting cycle, so to reduce female PPI by 15-20 days (shortening of 30-40%, in comparison to females reared with other females or in isolation respectively) In the last investigation on the subject we revealed that sexual interactions may start much sooner than previously thought in this species, and suggested that the observed male effect may likely result from early mating stimulations Here we tested the specific effect of controlled mating interactions (one or two mating events at different times) on female PPI We revealed that male presence for the time that allowed a single mating to occur (about 2 h) was enough to reduce the female intermoult by about 10 days (shortening of 19% in comparison to females reared in similar conditions but in the absence of mating interaction) Moreover, results indicate that the earlier and longer the copulations the stronger the 'male-effect' Altogether, the data support the conclusion that A vulgare females are able to adjust their reproductive physiology according to the presence/absence and the intensity of male mating stimuli We place the findings in a broader ecological context, revise the so far prevailing view on the 'male-effect', and stress on its possible significance in relation to the occurrence of feminising bacteria in this and other terrestrial isopod species
This study investigates the reproductive strategies of the pill-box crab, Halicarcinus cookii on the Kaikoura Peninsula, New Zealand. Various aspects essential to understanding reproductive strategies were examined including growth, population dynamics, reproductive biology and mating behaviour. H. cookii exhibits obvious sexual dimorphism such that females develop wide abdomens forming brood chambers, and males tend to grow larger than females and have larger chelipeds in relation to body size. H. cookii allocates energy into growth and reproduction in separate phases of its life cycle where growth ceases as reproductive maturity begins due to a terminal/pubertal moult. Despite the presence of ovigerous females throughout the 15 month sampling period, the population was highly seasonal, with peaks in recruitment and growth occurring primarily during the winter months and peaks in numbers of mature individuals during the summer months. Reproductive output increased with body size in H. cookii, as larger females produced more eggs and larger males transferred more sperm than their smaller counterparts. Ovaries matured prior to the terminal/pubertal moult (anecdysis) and, in multiparous females, in synchrony with brood development, allowing females to produce broods in quick succession, maximising their reproductive output in their short life span (approximately 12-18 months, 6 months as an adult). Incubation duration of broods decreased as seawater temperature increased, suggesting that temperature is the primary cause of the seasonal population cycling. Sperm storage allowed females to produce at least 4 fertilised broods without re-mating. Some sperm mixing in the spermathecae appeared to occur and the ventral-type structure implies last male sperm precedence. Males therefore preferentially mated with females closest to laying a new brood and guarded them longer than other females to ensure their paternity. Guarding duration varied according to the sex ratio allowing males to maximise their reproductive output.
A trade-off is found between growth and the length of time male amphipods (Gammarus lawrencianus) spend in amplexus. Males spending the majority of time in amplexus showed 45% less growth than unamplexed males. The inability of males to use their gnathopods to feed while in amplexus appears to cause this reduced growth. Growth rates of females appear unaffected by amplexus. Since male size is correlated with male reproductive success in G. lawrencianus, a 45% decrease in size increment at the next molt would represent a similar loss in the incremental male reproductive success. Male mating decisions are therefore based not only on immediate past male investment in amplexus, male size, and population characteristics, but also on the trade-off between present reproduction and future size.
Isopod Crustacea are ubiquitous and have a long evolutionary history. Their success may have been aided by their mating systems, of which an important feature is internal insemination. This work presents an overview of the function of isopod genitalia, with some discussion of their evolutionary aspects. Isopods have varying degrees and kinds of precopula, and the actual copulation has been described in detail only a few times. Mating generally takes place during the isopodan biphasic molt, although some groups have extended receptive periods. The nonmotile, "pennantlike" sperm are grouped into "spermatophores" that may be necessary for sperm transfer during internal insemination. Primitively, the male genital papillae are on the coxae of the last walking legs, but in most isopods they have moved onto the last thoracic sternite or, in some taxa, onto the pleotelson. Sperm transfer may be mediated by the appendix masculina of the male second pleopod, although this appendage's morphology shows a great deal of diversity. In the simple and primitive form, the second pleopod has a rod on the medial ramus. The copulatory function of this rodlike appendix mascu-
We examine the reproductive anatomy of both sexes of the isopod Thermosphaeroma thermo‐philum using SEM and light microscopy, and study the occurrence of multiple paternity using allozyme electrophoresis. Female reproductive openings are found ventrally, under the cuticular plate covering the body between the fifth and seventh pereonites. Receptivity for copulation is short during the sexual moult. Sperm from copulation are stored within the oviducts, close to the ovary, for up to two weeks before fertilisation and oviposition into ventral brood pouches. Sperm are not stored between broods. Male genitalia consist of penes with erectile extensions, and curved, channelled appendices masculinae. We suggest that appendices masculinae either channel sperm from the penes to oviduct openings located beneath the cuticular plate, or are used to push aside the cuticular plate for penile intromission. Paternity analyses suggest that multiple paternity is uncommon and that precopulatory guarding is an effective mate monopolisation strategy for males. We discuss the evolution of reproductive anatomy in the context of intersexual conflict, and suggest that conflict resolution may play a prominent role in the evolution of temporally restricted receptivity, male mate guarding, sperm storage, and delayed oviposition.
The endangered species (Federal endangered species list), Thermosphaeroma thermophilum, or “¿�Socorro Isopod,â€is endemic to a small spring near Socorro, New Mexico, that is thermally stable year-round. Isopods were observed in the field, and monthly samples were collected between March 1978 and February 1979 for laboratory examination. Males were larger than females, and sex ratio in the habitat was consistently biased toward males, particularly when sexually receptive females were abundant. Reproduction occurred primarily, although not exclusively, in spring and fall. Food seemed scarce, and intense predation by the omnivorous isopods appeared to exclude most invertebrate species, including predaceous aquatic insects, from the habitat. Fish do not inhabit the spring and avian predation is minimal or non-existent, perhaps permitting isopods to reach high densities and decreasing risks associated with male mate-searching behavior. Field and laboratory data indicated that isopods live less than 1 year. Males grow and reach sexual maturity faster than females. No evidence of hermaphroditism or sex-change was observed. Females were iteroparous and brood size increased with a female's age, but females were small and varied little in size, suggesting selection for an optimal female size.
Precopulatory mate guarding in crustaceans is a common male mating strategy when female receptivity for copulation is short. The decision to start guarding is not made by only males, however; it is commonly found that females resist the guarding attempts of males. Furthermore, experimental data show that males aim for longer guarding durations than females allow. Shorter guarding durations may be favored by females because of a number of potential costs of guarding. Precopulatory guarding therefore presents a model case of intersexual conflict where the fitness maximizing strategies of males and females differ. When the interests of the sexes are in conflict, the actual guarding duration may be a compromise between mat and female optima, resulting from the adjustment of contest behavior to the fitness gains of winning and to the fighting abilities of the parties. Intersexual conflicts are also likely to generate sexual selection on male and female traits related to the outcome of the contests.
In species with time-limited opportunities for insemination, precopulatory mate-guarding is expected to coevolve with the duration of female reproductive cycles. Despite this adaptation to female characteristics, it may also be advantageous for males to adjust the duration of guarding with respect to sex ratio because the benefits of guarding are dependent on the availability of females. If female fitness is reduced because of guarding, male guarding behavior leads to intersexual conflict. We studied these aspects of male mate-guarding behavior in two closely related, thermal-spring isopods (Thermosphaeroma). First, guarding duration showed species specificity which was related to the duration of reproductive cycle; cycle length for females and duration of guarding by males in T. milleri were twice as long as in T. thermophilum. Second, males in both species adjusted their guarding duration with sex ratio, guarding longer when a competing male was present. Third, in T. thermophilum, ovarian development began immediately after the birth of the previous brood and continued through guarding, sexual molt and post-molt periods until oviposition, whereas in T. milleri, ovarian development was largely postponed until the post-molt period. Because guarding during ovary provisioning periods may be costly for females, we tested the existence of intersexual conflict over guarding duration in T. thermophilum. We compared the duration of guarding of control pairs with those of pairs in which either male guarding ability or female ability to resist guarding was reduced experimentally. Guarding durations for manipulated and control males were equal, but manipulated females were guarded longer, suggesting that conflict exists and that females can effectively shorten guarding duration by their behavior. Moreover, we suggest that selection in the context of intersexual conflict may play an important role in the evolution of delayed oviposition and sperm-storage organs in mate-guarding crustaceans.
In the desert woodlouse Hemilepistus reaumuri monogamy and kin recognition have been found. To understand the evolution of this behavior, the mating system of the related subsocial woodlouse Hemilepistus elongatus was examined. This species shows maternal broodcare. If some of these woodlice were put together for some days in our experiments, almost all males had progeny with almost all of the females. However, if two males and one female were put together for 24 hr only, most juveniles were fathered by the male with the higher share of the first 10 copulations. Generally, the heavier male was the superior male in agonistic interactions. Superior males fathered more offspring. If two males were paired with a female one after another for 24 hr each, the first male fathered the majority of the offspring. The reproductive success of the second male increased, if it was paired with the female 48 hr after the removal of the first male. An explanation for these findings was found in the morphology of the spermatheca, which consists of a chitin tube and a surrounding cavity. In virgin females the chitin tube is closed. Some time after fertilization the tip of the chitin tube dissolves and sperm and sperm bundles fill the surrounding cavity. Mate guarding was not observed. The mating system found in H. elongatus cannot be used to model the evolution of monogamy in Hemilepistus sensu stricto.
[In dieser Arbeit wird versucht, beim terrestrischen Isopoden Venezillo evergladensis den relativen Beitrag zu schatzen, der nach Paarung eines Weibchens mit mehreren Mannchen hintereinander von diesen zu den resultierenden Mischungen gespeicherten Spermas geleistet wird. Mit Hilfe von drei die Farbmuster kontrollierenden Genloci lassen sich die Beitrage von 2-3 aufeinanderfolgenden Mannchen identifizieren. Mehrfache Besamung fuhrt zu Spermamischungen, bei denen das erste Mannchen groseren Befruchtungserfolg erzielt als das zweite und dritte, und das zweite einen groseren als das dritte Mannchen. Vorrangiger Befruchtungserfolg durch das zuletzt gekommene Mannchen existiert nicht. Jungfrauliche oder junge Weibchen bieten den Mannchen groseren Fortpflanzungerfolg, so das die Selektion zweifellos jede Fahigkeit der Mannchen begunstigen durfte, solche Weibchen zu erkennen. Die Vorteile der Spermamischung sind folgende: 1. Die Frequenz von Vollgeschwistern in der Nachkommenschaft eines Weibchens nimmt ab. Da Paarungen von Vollgeschwistern zu einer Minderung des Fortpflanzungserfolgs fuhren, bietet der Anteil von Halbgeschwistern an der Nachkommenschaft eines Weibchens die Moglichkeit, dem entgegenzuwirken. 2. Langandauernde Spermaspeicherung verbessert die Stabilitat von Polymorphismen. 3. Die effektive Populationsgrose ist groser, als es auf Grund der Anzahl lebender Individuen den Anschein hat. Dadurch verringert sich die Wahrscheinlichkeit von Auswirkungen von Gendrift., In dieser Arbeit wird versucht, beim terrestrischen Isopoden Venezillo evergladensis den relativen Beitrag zu schatzen, der nach Paarung eines Weibchens mit mehreren Mannchen hintereinander von diesen zu den resultierenden Mischungen gespeicherten Spermas geleistet wird. Mit Hilfe von drei die Farbmuster kontrollierenden Genloci lassen sich die Beitrage von 2-3 aufeinanderfolgenden Mannchen identifizieren. Mehrfache Besamung fuhrt zu Spermamischungen, bei denen das erste Mannchen groseren Befruchtungserfolg erzielt als das zweite und dritte, und das zweite einen groseren als das dritte Mannchen. Vorrangiger Befruchtungserfolg durch das zuletzt gekommene Mannchen existiert nicht. Jungfrauliche oder junge Weibchen bieten den Mannchen groseren Fortpflanzungerfolg, so das die Selektion zweifellos jede Fahigkeit der Mannchen begunstigen durfte, solche Weibchen zu erkennen. Die Vorteile der Spermamischung sind folgende: 1. Die Frequenz von Vollgeschwistern in der Nachkommenschaft eines Weibchens nimmt ab. Da Paarungen von Vollgeschwistern zu einer Minderung des Fortpflanzungserfolgs fuhren, bietet der Anteil von Halbgeschwistern an der Nachkommenschaft eines Weibchens die Moglichkeit, dem entgegenzuwirken. 2. Langandauernde Spermaspeicherung verbessert die Stabilitat von Polymorphismen. 3. Die effektive Populationsgrose ist groser, als es auf Grund der Anzahl lebender Individuen den Anschein hat. Dadurch verringert sich die Wahrscheinlichkeit von Auswirkungen von Gendrift.]
Accounts in the literature of precopulatory mate-guarding in gammaridean amphipods are that males use one of two strategies for mating: either they mate-guard by carrying or attending their mates until they are ready to molt and be fertilized, or they do not guard, instead searching benthically or swarming pelagically at the time that females are ready to molt. Mate-guarding by carrying has been documented for species of the superfamilies Gammaroidea, Talitroidea, and Hadzioidea. Mate-guarding by attending has been found in the more sedentary Corophioidea and Caprellidea. Non-mate-guarders that search pelagically are species of Ampeliscoidea, Lysianassoidea, Phoxocephaloidea, Oedicerotoidea, and Pontoporeioidea. Non-mate-guarders that mate-search benthically are species of Eusiroidea, Crangonyctoidea, and Haustorioidea. Mate-guarding and non-mate-guarding males develop different secondary sex characters at maturity. Mate-guarding males have enhancements for fighting and signalling. These alterations are more elaborate in males that attend their mates than in males that carry their mates. Non-mate-guarders that search pelagically develop enhancements for swimming and sensing. Non-mate-guarders that remain benthic exhibit little change at maturity. Most mate-guarding males develop their secondary sexual characters over several molts and mate over more than one instar. Pelagic mate- searchers develop their secondary sexual characters at the last molt and mating is confined to the last instar. Females of most mate-guarding species are iteroparous, while fewer than half of non-mate-guarding species are so. It is hypothesized that mate-guarding arose more than once in the evolutionary history of amphipod Crustacea.
Inheritable differences in life history features are shown among three groups of populations of Hyallela azteca from Oregon. Hyallela individuals of coastal populations are relatively small as eggs, as young, and as adults. They grow slowly as young and adults, and the regression of clutch size on female size is relatively steep. Hyallela individuals from the Cascade Mountains are large as eggs, as young, and as adults. They grow rapidly as young and adults, and the regression of clutch size on female size is relatively less steep. A population of Hyalella from a hot springs is made up of animals that are intermediate in these characteristics. The maturation period and the rate of production of egg volume does not differ among the populations investigated. Selection for inconspicuousness, generated by visually orienting predaceous fish, is probably responsible for the small, slow-growing end of the character spectrum (coastal populations). Hyallela is a grazer and deposit feeder, it does not filter. Evidence indicates that larger Hyalella do not have a competitive advantage in predator-free environments, as do larger planktonic filter feeders.
The aquatic isopod, Lirceus fontinalis Rafinesque, occurring in granite gneiss weather pools on Mount Arabia, DeKalb Co., Ga., was investigated with respect to behavior patterns, interactions between the isopods and various environmental stresses, and determination of the major factors or combinations of factors that control the distribution and abundance of the isopods. Drought and high temperatures are the two major limiting factors controlling the Lirceus population. The capability of individuals to survive drought stress is reduced by acute exposure to high temperatures. Klinokinetic responses to standing water and orthokinetic responses to moisture contribute to the ability of individuals to survive drought stress by bringing about aggregations in or on top of moist sand under rocks. Rheotactic responses to rapidly flowing water account for repopulation of weather pools by bringing about emigrations from an intermittent creek to the pools, as confirmed by the movement of Zn-65-labeled isopods. High temperatures have an inhibiting effect on the rheotactic response. Isopods seldom venture from the dark recesses of rocks piled in weather pools because of a negative photokinetic response. Implications of a 43 factorial experiment on the interactions of gamma radiation, high temperature, and drought stresses are that introduction of ionizing gamma radiation into the habitat for even brief periods at 16,400 R/hr would severely lower the ability of the population to withstand high temperatures and drought.
The population dynamics and bteeding biology of Idotea baltica, I. chelipes and I. granulosa wete studied in the littoral belts of two northern Baltic rocky shore habitats. Population sizes are largest in the aurumn, after occupation of the Fucus belt by a new Idotea generation from the belt of filamentous algae. Two periods of dectease in the population density, one in late autumn and another after the breeding period in the following summer were observed. Adult males are eliminated from populations before females. Most individuals in each species breed simultaneously in eatly summer. Brood numbers are related to female size, but great marsupial mortality occurs during incubation. Idotea juveniles grow exp.nentially in late summer, but during winter the growth is delayed. Another period of intensive growth occurs in spring before breeding. I. baltica is the dominant species in both habitats examined. I. chelipes and I. granulosa were found not to coexist. The roles of different factors affecting the distribution and geographical variation in Idotea are discussed.
1. A large breeding population of Idotea emarginata is described, and an account of development, growth and reproduction is given. 2. In the adult brood-pouch the embryo passes through four distinct stages, and the embryos in the brood-pouch of any one female are all at the same stage of development. 3. The characteristics of the first three free-living stages are described, but beyond this it proved impossible to separate the stages. The growth of the antennule, antenna and telson, and the appearance of adult sexual characters, are described. 4. There is an overwintering population of large males and females, which die off in spring, and of juveniles which do not begin to grow until spring. Mass release of young, which immediately began to grow, took place in April and September-October 1952, and April-May, July, and October 1953. 5. These observations are discussed in relation to other species of Idotea.
This report describes mating behavior in the terrestrial isopod, Venezillo evergladensis, relating female receptivity and molting cycle. A brief review of molting and mating in isopods precedes the data and a description of the observational method appears in sufficient detail to permit duplication. Males orient to receptive females using olfactory clues. Visual recognition appears absent. The male initiates mating by actively tapping the female's cephalon with his antennae. The female's two gonopores are inseminated by separate acts of copula, each preceded by a nuptial ride. Virgin females mate during the intermolt period or just prior to a growth molt. Their first parturial molt is the second molt following the mating. Females no longer elicit male attention shortly after a mating. They again elicit male mating behavior (1) shortly after birth of a brood of young before loss of the brood pouch by a molt, and (2) just prior to the subsequent parturial molt. In the former case, females were not receptive to the males. A single mating likely occurs for each brood of young. The large older males dominate small younger males in competition for mates. Young virgin females most likely mate with older males of a preceding generation, constituting a mating system adding stability to genetic variation.
The proportion of the female molt cycle spent in amplexus varies inheritably among several populations of the talitrid amphipod Hyalella azteca. Duration of amplexus is negatively correlated with an index of the intensity of predation by visually orienting fish. As amplexus renders the amphipods more vulnerable to these fish, I hypothesize that this type of predation selects for an abbreviation selects for an abbreviation of the amplexed phased of the female molt cycle.
The reproductive sequence of Caprella laeviuscula Mayer consisted of pair formation, female molting, copulation, pair disengagement, and egg laying. The male held the female with the fifth pereiopods during precopula and removed the exoskeleton of the female prior to copulation. The number of eggs carried by the female was a function of female size, and the number of juveniles carried was significantly lower than the number of eggs carried by similarly sized females. Some of the eggs may have functioned as nurse eggs. Cephalon length was determined to be the best character for analysis of sexual dimorphism in this species. Among sexually mature specimens, males had more rapid differential growth of pereionites 1 and 2, while female pereionites 3-7 grew more rapidly. In addition to exhibited growth rates, sexual dimorphism was evident in the brood pouch of females, and in the point of insertion of gnathopod 2. The differences could not be related to male-female reproduction, and sexual dimorphism of males probably is a response to the male-male aggressive interactions during precopulation.
The breeding system of the freshwater amphipod crustacean Gammarus pulex (L.) contains a precopulatory phase during which a male carries a female. The seasonal changes in this behaviour were studied in a stream and in a pond population. The length of the guarding phase varied considerably over the seasons. In the stream, larger animals of both sexes were at an advantage in reproductive competition and the advantages were greatest at the peak of the breeding period. Animals of both sexes infected with a cystacanth of the parasite Polymorphus were less likely to be paired than were non-infected individuals. In the pond, the life cycle was more similar to that of a lake population of G. lacustris Sars than to the stream population. Pairs were more vulnerable to fish predation than were unpaired males. It is suggested that fish predation prevented all year breeding. /// Система спаривания пресноводных амфипод Gammarus pulex (L.) включала прекопулятивную фазу, в течение которой самец удерживает самку. Сезонные изменения в зтом поведении исследованы на речной и прудовой популяции. Длительность охранной фазы сопровождения сарьировала в разные сезоны. В реке крупные животные обоих полов имели преимуцества в репродуктивной конкуренции, и преимуцества были наибольшими в период пикаспаривания. Животные обоих полов, зараженные цистами паразита Polymorphus спаривались менее активно, чем незараженные. В пруду жизненный цикл более сходен с таковым у озерной популяции G. lacustris, чем у речной. Спариваюциеся особи были более подвержены хицничеству рыб, чем неспариваюциеся самцы. Установлено, что хицничество рыб препятствует размножению в течение всего года.
Three discrete male morphs coexist in Paracerceis sculpta, a marine isopod crustacean inhabiting the northern Gulf of California. Ornamented α-males establish themselves in the spongocoels of intertidal sponges, where females congregate to breed. Smaller β-males, resembling sexually mature females, enter spongocoels by deception, while tiny γ-males invade spongocoels by stealth. Isopods breed year-round, and the operational sex ratio fluctuates widely over short durations. When females are abundant, receptive females accumulate in spongocoels, and these spongocoels are preferentially invaded by β- and γ-males. To test the hypothesis that the density of receptive females affects relative fertilization success among male morphs, individual β- and γ-males, heterozygous for a dominant cuticular pigmentation allele, were placed in artificial spongocoels with an unmarked α-male and densities of one, two, and three unmarked, receptive females. The fertilization success of each male was determined by counting the number of marked and unmarked progeny each female produced. Alpha-males guard females effectively and sire nearly all young when one female is in a spongocoel. The success of β- and γ-males increases, however, and may even exceed the success of α-males when two or three females are present. The regular occurrence of more than one receptive female in the harems of α-males may contribute to the persistence of β- and γ-males in this species.
Paracerceis sculpta breeds in intertidal sponges, Leucetta losangelensis, where males employ 1 of 3 discrete alternative reproductive behaviors. Elaborate alpha-males attract females to spongocoels where mating and brooding of young by females occurs. Variance in the number of females per alpha-male is high (N = 0-11). Smaller beta-males, resembling females, and tiny gamma-males, resembling juveniles, invade spongocoels containing alpha-males and sexually receptive females. Alpha-, beta-, and gamma-males maintained in the laboratory do not molt or grow, and the 3 morphs differ in the relative amounts of energy they invest in somatic versus gonadal tissue (gamma > beta > alpha). Alternative male reproductive behaviors may have evolved in P. sculpta, since intensifying sexual selection on alpha-males allowed only the most competitive alphas to mate. Males that obtained mates by avoiding direct competition with alphas (e.g., mimicking females or stealing mates) may have persisted, despite their reduced fitness, because they experienced greater fitness than competitively inferior alphas. Similar selective pressures and thus similar male polymorphisms probably exist in other Crustacea.
Seasonal changes in the intertidal distribution, abundance and population dynamics of the epifaunal amphipod Gammarus palustris were studied in salt marshes bordering 2 estuarine rivers flowing into the Chesapeake Bay. The amphipod populations inhabiting the Patuxent River study site showed abundance peaks during the spring and autumn, and major declines in density during the summer and winter. Populations at 2 study sites in the Rhode River showed only 1 peak of abundance during the late spring and early summer which was followed by a decline in density throughout the remainder of the year. In both rivers, the low amphipod densities observed during the winter corresponded with a subtidal migration. Migrations did not account for the low numbers observed at other times and an examination of the life cycle of this species as well as an egg-ratio analysis of the populations indicated that low densities during the summer (Patuxent) or late summer and fall (Rhode) were not due solely to life-cycle events. The tolerance of G. palustris to 3 environmental parameters was tested in the laboratory. These included low-salinity, heat/desiccation and freezing-stress experiments. Comparisons of the results with observed fluctuations of these variables at the study sites demonstrated that only freezing stress would probably cause significant mortality in intertidal populations of this species. Insufficient tolerance to this stress was postulated as the reason for the observed distributional shift to subtidal areas during the winter. Amphipod distribution within the intertidal zone at other times of the year was highly correlated with Spartina density. Substratum preference experiments indicated that this was due to a strong behavioral preference by this species for Spartina culms. Intraspecific and interspecific competition for food were tested by an analysis of 3 reproductive indices: the estimated birth rate as calculated by the egg-ratio method, the average brood size and the average brood size/ovigerous @V. The former 2 indices declined during the early summer as a result of natural adult female mortality and a decreased proportion of ovigerous to nonovigerous @V @V. The average brood size/ovigerous @V did not decline significantly throughout the reproductive period indicating that food limitation did not induce the observed summer decline in amphipod abundance. Intraspecific competition for space was tested in the laboratory by crowding and competitive-displacement experiments. The results indicated that competition for space was not directly responsible for the summer decrease in amphipod density but did influence amphipod distribution when Spartina culms were a limited resource. In this situation, G. palustris was capable of intraspecific displacement and evidence is presented which indicates that adults are able to displace juveniles from the preferred substratum. Interspecific competition was not examined experimentally because most of the associated fauna inhabiting the marsh beds were infaunal species. Laboratory predation experiments showed that 3 species, Fundulus heteroclitus, Rhithropanopeus harrisii and Paleomonetes pugio could potentially regulate G. palustris densities. Furthermore, F. heteroclitus predation decreased significantly with increased Spartina density and was strongly size selective for large amphipods. Rhithropanopeus harrisii and P. pugio predation was not significantly affected by Spartina density when amphipod abundance was low and predation by both species was significant with high amphipod and culm density, similar to that observed at the Rhode River sites. Although adult R. harrisii showed some indication of size selective predation, neither species was strongly size selective for large G. palustris when Spartina culms were dense. Field caging experiments combined with estimates of predator density indicated that Fundulus predation was the primary source of mortality in the Patuxent River population during the summer. The results of caging experiments in the Rhode River were inconclusive but large increases in predator density correlated with major declines in amphipod abundance. Therefore, predation is postulated as the major source of mortality during the summer and fall at the Rhode River sites. Thus, both environmental and biological factors regulate these amphipod populations with the former important during the winter only and the latter important at other times of the year.
The duration of embryonic development in Gammarus pulex L. was studied in relation to environmental temperature. Bělehrádeks equation was fitted with the data. The expression used was logD= loga+ blogT+ c( logT)2. The offspring of successively reproducing females was bred in the laboratory for one year at stimulated natural temperatures. Turnover rate and production was calculated for the descending population at conditions prevailing. The ratio of the production of the descending generation to the original biomass of its parents ( P/ B0) was 7.1. /// Исследовали длительность эмбрионального развития у Gammarus pulex L. в зависимости от температуры среды. Использовали уравнение Белерадека для анализа данных. Выражение имеет вид: log D= log a+ b log T+ c( log T)2 Потомство у самок выращивалось в лаборатории тод при температурах, близких к естественным. Скорость круговорота и продукция рассчитывались для нисходящих поколений при существующих условиях. Отношение продукции нисходящего поколения к исходиой биомассе родительского поколения ( P/ B0) составляло 7,1.
The mating system of the freshwater amphipod Hyalella azteca consists of precopulatory mate guarding, in which males compete for the possession of females by guarding them before copulation. Although males in the field population are on average significantly heavier than females, males in precopula are not proportionately heavier than the females they carry, indicating that precopulatory mate guarding takes place in a nonsize assortative manner. In the laboratory, the guarding pattern and pairing success are dependent upon the operational sex ratio (OSR). When the OSR is female-biased, males are more successful at obtaining females due to the active male mate choice, but when OSR is male-biased, females are less frequently taken into precopula because of intensified male-male interference. At female/male OSR values of 1:2 or 2:1, males demonstrate a preference for large prospective mates. However, at the OSR values of 1:3 or 3:1, pairs are randomly formed with no size-dependent responses. This flexibility of guarding behavior is explained by time and energy investment tactics in mate selection by both sexes.
Males are produced in long day photoperiods and females in short days. Populations are characterized by fluctuating sex ratios and marked sexual size dimorphism. Males are always larger than the female they carry in precopula. The life cycle of G. duebeni in N England is annual and is restricted by temperature. Overwintering adults breed early in the year and die by August. Generations do not overlap. Sex ratio during breeding is female biased, then becomes male biased due to massive recruitment of young males early in the year. Recruitment late in the year is exclusively female. Sex ratio changes are due to sex differential production rather than differences in growth or mortality. Larger females produce more eggs and larger males are paired with larger females, but because of the mating pattern, males benefit relatively more from large size than do females. Early produced animals have a long growth period and will be large in the next year; they maximize fitness by becoming male. Late animals are growth restricted and minimize loss of fitness by becoming female. -from Authors
Precopulatory guarding in Crustacea is usually analyzed as a male decision problem. We suggest an alternative possibility that precopula is established as a result of intersexual conflict over precopula duration. Such a conflict can be expected when the male optimum for precopula duration exceeds the female optimum. As a result, males should start precopulatory attempts earlier, while females should resist until close to receptivity. Our analysis reveals two potential sources of conflict: (1) sexual differences in survival probabilities before and during the mate-guarding; and (2) sexual differences in the probability of finding a mate. The latter is perhaps a more probable source of intersexual conflict, since male biased operational sex ratios are common in mate-guarding Crustacea. The former requires that female moulting cycle is synchronous, whereas the latter may operate in populations with asynchronous moulting cycles as well. We further studied the expected intensity of behavioural conflicts in terms of expected present and future fitness gains. In the beginning of the female moulting cycle, there is no conflict. Conflict arises as males start the guarding attempts and females are motivated to resist, and ceases with a decrease in the female's motivation to resist. Several assumptions and predictions of the model are discussed and compared with the behavioural patterns observed in the aquatic isopod Idotea baltica.
Most females of the terrestrial isopod species Armadillidium vulgare and A. nasatum, which have mated once, store functional sperms until they die, thus assuring a normal number of broods without additional matings. Using colour genes (sex-realisators) it could be demonstrated that, in Armadillidium peraccae and A. nasatum, offspring of females that had been mated a second time, after an interval of some months to about one year, usually include descendants of the second male; often these predominate, and sometimes none from the first male are present. Hence, in spite of the potential long life-span of the spermatozoa, it is possible to obtain progeny of at least two males from one female. But it is essential to be able to distinguish the descendants of the males used for experimental purposes, since each brood may have offspring from both of them.
We employed field-based studies, with complementary laboratory-based studies, to investigate social and environmental influences on tactical mate-guarding decisions in amphipods (Crustacea). Firstly, we investigated variation in precopulatory mate-guarding duration in Gammarus duebeni celticus in relation to the social structure of natural populations. Variation in population density of up to two orders of magnitude had no effect on precopula duration, whereas guarding durations increased as the sex ratios of the populations became more male biased. That is, males have some ability to assess the probability of other males taking females into precopula and are prepared to guard for longer as this threat of male: male competition increases. A field demonstration of tactical shifts in reproductive behaviour in response to pertinent social conditions is thus provided. Secondly, the 'habitat segregation' hypothesis, which proposes that positive size-assortative pairing in amphipod populations arises due to variation in the use of micro-habitats, was tested in natural held populations and under laboratory conditions in Echinogammarus marinus. This was necessary in order to distinguish any purely environmental determinants of size-assortment from the role of active decisions by males concerning mate choice and male: male competition. The hypothesis was rejected on the grounds that size-assortative pairing arises under both heterogeneous and homogeneous environmental conditions. Further, in both study species, male and female body size were positively correlated with precopula duration. Thus, indirect competition for access to large, fecund females, based on the timing of male entry into precopula, together with direct aggression, provides the explanation for size-assortative pairing in amphipods.
Time investment strategy is defined as the optimum allocation of times spent on given activities so as to achieve maximum reproductive success. Selective pressures on males to increase time invested in encountering females would be least in sessile and communally spawning species, and maximum in mobile species which spawn at low density and those which copulate. The present paper concerns male time investment in courtship persistence and female-guarding. Staying with a given female reduces the rate at which new females are encountered. Females are often unreceptive for some time after mating. Males often court unreceptive conspecific females; they can achieve a gain if the female rejection reactions can be overcome (rape) and the ejaculate can compete in the fertilization of the ova. Courtship of unreceptive females of closely related sympatric species is also considered adaptive. Though female unreceptivity will be favoured if hybrids are disadvantageous, males may gain by attempting rape if the fitness of hybrid offspring is high enough and the time investment favourable. A model is constructed to explain how optimum persistence durations are determined. This depends on 1) how the cumulative probability of insemination changes through time invested, 2) the encounter frequency, 3) the ejaculate cost (measured as feeding time investment/ejaculate), and 4) is modified by the pattern of gain from other types of female. Females can adapt to male persistence either by acceptance, by increasing rejection effectiveness, or by dispersing into another area where it is disadvantageous for males to search. This last solution may have been especially important in sympatric speciation. Male courtship duration with potentially receptive conspecific females may also be optimized. Variation in male persistence time may be due to assessment of particular situations. Female guarding has commonly evolved as a male time investment strategy. Precopulatory guarding appears to function to stake a claim to a female (or females) until she becomes receptive. This poses two problems : at what point in the female's reproductive life does it become advantageous for the male to guard, and how is guarding time optimized? Optimum guarding duration can be determined with the same model as for courtship persistence. If males adopt a given cue for closeness to receptivity for the onset of guarding, females showing the cue become scarce and selection may favour drive for earlier and earlier cues. This could be stabilized by the opposing selective pressures of 1) chances of finding a female closer to mating high enough, 2) female distribution suitably non-random with respect to mating, and 3) guarding investment more costly than searching investment in terms of male future reproductive success. Postcopulatory guarding appears to function to prevent loss in gain to a male due to sperm competition from other males. Such behaviour could evolve in conditions of high female receptivity and high encounter rate during an adequate overlap period (time per female during which ejaculates from different males can compete for fertilization of the ova), since males which guard after mating may waste less time and sperm than non-guarders. Its advantage is increased by a male-biassed sex ratio during the overlap period. The behaviour depends on the fact that second matings can compete in the fertilization of the ova, and postcopulatory guarding has its higlest advantage when the last male to mate fertilizes most eggs. Optimum guarding duration can be determined with basically the same model as before, and depends mainly on how sperm utilization is distributed within the overlap period.
The following observations are presented :-1) A description of male: female interaction in A. aquaticus and A.meridianus. This indicates the presence of a male discrimination mechanism in that large females are selected for the passive phase before their smaller counterparts. 2) Passive phase durations in allopatric and sympatric populations of A. aquaticus and A. meridianus. No significant difference was found between species; however two populations of A. meridianus differed significantly from each other (<0.05P). The duration of passive phase is shown to be substantial (means varying from 5.3-11.2 days). Intermittent pairing was shown to occur, in particular with small females. 3) The relationships between the parameters a) female size: day the passive phase commenced for each couple and b) female size: day each female became ovigerous. That is large females were found paired and became ovigerous before their smaller counterparts. Both relationships are shown to be significant (at 0.05 level of probability or less) in four of the five populations investigated. It is suggested these observations may be interpreted in the following way: Males of both species are selecting for passive phase association those females exhibiting a cue which correlates with imminent oviposition and large brood size. This cue may be female size or another characteristic which is correlated to size. This behaviour pattern yields an increase in offspring number to those males exhibiting it.
The following observations are presented :-1) A description of male: female interaction in A. aquaticus and A.meridianus. This indicates the presence of a male discrimination mechanism in that large females are selected for the passive phase before their smaller counterparts. 2) Passive phase durations in allopatric and sympatric populations of A. aquaticus and A. meridianus. No significant difference was found between species; however two populations of A. meridianus differed significantly from each other (<0.05P). The duration of passive phase is shown to be substantial (means varying from 5.3-11.2 days). Intermittent pairing was shown to occur, in particular with small females. 3) The relationships between the parameters a) female size: day the passive phase commenced for each couple and b) female size: day each female became ovigerous. That is large females were found paired and became ovigerous before their smaller counterparts. Both relationships are shown to be significant (at 0.05 level of probability or less) in four of the five populations investigated. It is suggested these observations may be interpreted in the following way: Males of both species are selecting for passive phase association those females exhibiting a cue which correlates with imminent oviposition and large brood size. This cue may be female size or another characteristic which is correlated to size. This behaviour pattern yields an increase in offspring number to those males exhibiting it.
The amphipod crustacean Microdeutopus gryllotalpa builds tubes on solid substrata. Mature animals usually reside in individual tubes. When more than one individual is present in a tube it is always a single heterogametic pair. Tube-sharing occurs with the greatest frequency 12 h before the female's moult. Following the female's moult, most males leave the tube. The pattern of tube-sharing is the behavioural analoque of precopulation in epibenthic amphipods. It is demonstrated that (1) no more than two individuals are found in a tube because (2) one individual will not permit another individual of the same sex to cohabit the same tube, and (3) the female determines the time of tube-sharing, for most females tube-share only shortly before they moult. It is hypothesized that after the male leaves the female's tube, he cruises from tube to tube until he gains entry into the tube of another receptive female.
Precopulatory mate guarding is the habit, practised by many species, of the two sexes' joining together in intimate pairs for some time, usually days, before mating. It is mainly found in species in which mating is confined to a very short period of the female's reproductive cycle. A mathematical model confirms that precopula will evolve when mating is restricted in time. The model also specifies the evolutionary stable duration of precopula. There are two models: in the simpler, males cannot take over paired females; in the second, larger males can take over females from smaller males. In the model with takeovers, larger males guard for less time than smaller males, and the average guarding duration for all males is shorter than in the model in which there were no takeovers.
[Nous avons vu que les jeunes stades de Naesa bidentata (Adams) se rencontraient le plus habituellement sur les algues, tandis que les adultes sont le plus souvent dans les anfractuosités des rochers, sous les pierres et dans les loges vides de balanes. Dans les coquilles vides de Balanus perforatus Bruguière on a trouvé jusqu'à cinq femelles, immatures, qui deviendront plus tard ovigères, accompagnant un seul mâle. Les adultes ne se nourrissaient apparemment pas et les femelles semblaient subir une résorption des tissues internes jusqu'à leur mort et leur expulsion par le mâle, après que les jeunes avaient été libérés de la poche incubatrice., Nous avons vu que les jeunes stades de Naesa bidentata (Adams) se rencontraient le plus habituellement sur les algues, tandis que les adultes sont le plus souvent dans les anfractuosités des rochers, sous les pierres et dans les loges vides de balanes. Dans les coquilles vides de Balanus perforatus Bruguière on a trouvé jusqu'à cinq femelles, immatures, qui deviendront plus tard ovigères, accompagnant un seul mâle. Les adultes ne se nourrissaient apparemment pas et les femelles semblaient subir une résorption des tissues internes jusqu'à leur mort et leur expulsion par le mâle, après que les jeunes avaient été libérés de la poche incubatrice.]
Three species of Limnoria occur together in Southampton Water. Migration began at a water temperature rising through 10°C in L. quadripunctata and L. lignorum and through 15°C in L. tripunctata, Migratory activity followed the water temperature in L. tripunctata but declined in L. lignorum before the highest temperatures were reached. The migratory behavior of L. quadripunctata resembled that of L. tripunctata at one site and that of L. lignorum at another. Overcrowding as a cause of migration was not supported. Migration was confined to large, sexually mature adults, excluding gravid females. The first migrants were predominantly male, and in L. lignorum about twice as many males as females migrated.
Reproduction showed a marked increase in the summer, beginning at a water temperature of 10°C in L. quadripunctata and L. lignorum and of. 12°C in L. tripunctata. L. quadripunctata differed from other species in being the only one in which the average brood size of post‐migrants was significantly greater than that of non‐migrants, and in which a significant increase in brood size with body size occurred. No seasonal change in brood size was demonstrated in any species. Widely separated developmental stages were frequently found in the same brood. The duration of the egg stage was longer than that of the embryo which in turn exceeded that of the larval stage.
Ligia exotica is aggregative, tending to seek out conspecifics. It is hypothesized that Ligia must seek new shelters repeatedly with changing tides because of their restricted water requirements, and that attraction to conspecifics already in a suitable habitat is an additional orientational mechanism to those external environmental factors influencing microhabitat selection. Experiments on object orientation demonstrated a strong tendency to move toward contrasting landmarks, the result being occupation of rocky areas on the shoreline. Brief descriptions of sexual and agonistic behavior are included.
In dieser Arbeit wird versucht, beim terrestrischen Isopoden Venezillo evergladensis den relativen Beitrag zu schätzen, der nach Paarung eines Weibchens mit mehreren Männchen hintereinander von diesen zu den resultierenden Mischungen gespeicherten Spermas geleistet wird. Mit Hilfe von drei die Farbmuster kontrollierenden Genloci lassen sich die Beiträge von 2-3 aufeinanderfolgenden Männchen identifizieren. Mehrfache Besamung führt zu Spermamischungen, bei denen das erste Männchen größeren Befruchtungserfolg erzielt als das zweite und dritte, und das zweite einen größeren als das dritte Männchen. Vorrangiger Befruchtungserfolg durch das zuletzt gekommene Männchen existiert nicht. Jungfräuliche oder junge Weibchen bieten den Männchen größeren Fortpflanzungerfolg, so daß die Selektion zweifellos jede Fähigkeit der Männchen begünstigen dürfte, solche Weibchen zu erkennen. Die Vorteile der Spermamischung sind folgende: 1. Die Frequenz von Vollgeschwistern in der Nachkommenschaft eines Weibchens nimmt ab. Da Paarungen von Vollgeschwistern zu einer Minderung des Fortpflanzungserfolgs führen, bietet der Anteil von Halbgeschwistern an der Nachkommenschaft eines Weibchens die Möglichkeit, dem entgegenzuwirken. 2. Langandauernde Spermaspeicherung verbessert die Stabilität von Polymorphismen. 3. Die effektive Populationsgröße ist größer, als es auf Grund der Anzahl lebender Individuen den Anschein hat. Dadurch verringert sich die Wahrscheinlichkeit von Auswirkungen von Gendrift.
A. aquaticus and A. meridianus have a passive phase in which the male carries the female for some days before moulting and copulation are possible. The effect of varying male: female ratios (0.5:1; 1:1; 1.5:1) is discussed in this paper. It was found that an increase in the proportion of males led to: a) earlier initiation of the passive phase; b) lower gain rates from paired females; c) an increased tendency for males to leave females; d) a reduction in the strength of the association between the timing of pairing and oviposition. The relevance of these observations to models of optimal female guarding and foraging strategies is discussed.
In a laboratory experiment in I. baltica the precopulatory guarding was preceded by a period of struggles between the sexes as males continuously tried to initiate the precopulatory guarding and females resisted their guarding attempts. This struggling lasted for a few days, during which the females escaped from the males on the average 1.3 times per hour. While the females resisted, the males usually responded by kicking back. Once the precopula started, on the average 43 h before the completion of the female parturial ecdysis, the female resistance stopped. If the guarding male was replaced by another male, the female accepted the new male without resistance or resisted only weakly. Larger males were able to perform longer precopulas, and furthermore, when males were hunger stressed they performed shorter precopulas than control males. The female resistance and the existence of struggles imply a conflict between the sexes over whether or not to start the precopulatory phase. This conflict may occur either because of different optimum precopula duration of the sexes or because of the unwillingness of the females to pair with whatever male. By resisting, females may, at least to some extent, control the duration of the guarding, and the resistance may lead to selection among male candidates. Thus the female resistance, although for so far largely neglected, may have potential importance in the mate choice and sexual selection of aquatic crustaceans with precopulatory guarding.
1. The predatory behaviour of the smooth newt (Triturus vulgaris) on the isopod Asellus aquaticus was studied and the typical predatory sequence described. 2. Male Asellus in precopula experience a reduced risk of predation relative to single males. They seem to show an antipredator behaviour which 'confuses' the newt. 3. Precopula was probably influenced by both natural and sexual selection during the course of its evolution in this isopod.
In the terrestrial Crustacean Armadillidium vulgare, the onset of female reproduction can be sped up by a male-induced stimulation. This male-effect is mainly characterized by a shortening of the vitellogenesis period, which occurs during the preparturial intermoult. The determinism of this phenomenon, for the first time reported by Jassem in 1982, was investigated here by both experimental and ethological approaches. It was shown that a male deprived of its copulatory organs is significantly less stimulating than an integrated one. On the other hand, a paired female with obturated genital apertures is significantly less stimulated. According to the literature, mating takes place only when vitellogenesis is nearly over and therefore cannot be related to the male-effect. Nevertheless, the ethological approach has revealed that females are early attractive for males, and that mating postures can be observed during the whole preparturial intermoult. In fact, insemination can happen as early as the initiation of the secondary vitellogenesis. Before this stage, short mating postures are still observed but no sperm was found in the female genital ducts (pseudocopulation). However, spermatozoa and other seminal substances are not implicated in this phenomenon since a male unable to ejaculate is as efficient as a normal one. Therefore, it is strongly assumed that the male-effect results from mating postures during which male copulatory organs act on mechanoreceptors located in the female genital apparatus.
The enzyme phosphoglucose isomerase (PGI) is encoded by a multi-allelic gene locus in North American populations of the wood louse Porcellio scaber. Laboratory crosses using virgin females have documented the Mendelian nature of PGI inheritance for seven electrophoretically distinct alleles. Several additional rare alleles occur in natural samples. This multi-allelic polymorphism has been employed to determine the frequency of multiple paternity of broods in a natural population by examining the mother-offspring (family) genotype combinations of 20 field-collected pregnant females. The data indicate that the great majority of broods (>80 per cent) are multi-paternal and that each of several males usually makes a substantial spermic contribution to any particular one.
A study was made of the life cycle and reproductive ecology of Gammarus duebeni in the Test Estuary on the south coast of England. The species is towards the southern limit of its distributional range in the north-east Atlantic, which results in breeding continuing throughout much of the year. The breeding strategy employed was found to vary with season. The size of eggs produced and the rate of egg production were both temperature dependent, whereas the proportion of production expended on eggs and the number of eggs per brood, although probably influenced by temperature appeared to be controlled by food availability and female size. Factors affecting the mortality of eggs within the marsupium and breeding synchrony were considered in relation to season. The life cycle consisted of two major overlapping generations.
The object of this research was to discover details of the life history and breeding biology of the two species of Asellus found in the surface waters of the British Isles. Data were obtained from monthly samples taken from two habitats. Analysis revealed that the species are similar in most aspects that were investigated but that the life histories show slight differences in timing.