Mating patterns in late-maturing female Mediterranean tarantulas may reflect the costs and benefits of sexual cannibalism

During courtship and mating, males of some invertebrate predators risk being killed and consumed by females, who in turn can obtain a foraging benefit from feeding on males. In these invertebrates, the sex ratio at the end of the mating season is usually female biased, probably due to sexual cannibalism and other sources of male mortality. Thus, at the end of the mating season males can be a limited resource to females as both mates and prey. Because of the high risk incurred when approaching females, males should show mate choice. To date there are little data on the costs and benefits of sexual cannibalism in natural populations. For one month we followed the mating patterns of 60 late-maturing Mediterranean tarantula, Lycosa tarentula L., females in a desert grassland population. The later a female matured, the shorter was her cohabitation time with males and the lower her probability of cohabiting with a male at all, suggesting that late-maturing females may be limited in their access to males as mates. At the end of the mating season, nonsexually cannibalistic late-maturing females also had poorer body conditions than did both sexually cannibalistic late-maturing females and early-maturing females, suggesting that late-maturing females may be also limited in their access to males as food. Females had higher mating success if they were smaller or in better condition (better fed). This pattern may reflect either male choice, or the possibility that small, well-fed females have higher mating success because they are less aggressive towards males. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

The Role of Body Size in Mating Interactions of the Sexually Cannibalistic Fishing Spider Dolomedes triton

Some arachnids display extreme sexual size dimorphism (SSD) with adult females being several times larger than adult males. One explanation for SSD in species that exhibit pre‐copulatory sexual cannibalism (female attack, kill and consumption of the male prior to mating) is that smaller males may be less likely victims of predatory attacks by females. However, in some sexually cannibalistic species SSD is relatively moderate (i.e. males are similar in size to females) suggesting benefits of large male body size. Here, I report the results of an experiment designed to explore the ramifications of body size in mating interactions of the sexually cannibalistic, North American fishing spider (Dolomedes triton). Results suggest that male size does not influence courtship behavior, the likelihood of being attacked, or the male's ability to secure a mounting. However, large males were superior at gaining copulations once mounted. Sexual cannibalism may also be predicated on female size. Female condition (mass/cephalothorax area) did not explain any of these behaviors from the copulatory sequence, however, females with a smaller cephalothorax area were more likely to attack courting males. Finally, analysis of the ratio of female size to male size showed that when SSD is weak males are more likely to escape attacks and mate successfully. Results are discussed in light of several hypotheses for sexual cannibalism, and the benefits of large male body size illustrated here are put forth as potential explanations for the relatively moderate extent of SSD found in this sexually cannibalistic species.     

Seasonal aspects of sexual cannibalism in the praying mantis (<Emphasis Type="Italic">Mantis religiosa</Emphasis>)

According to the adaptive foraging hypothesis of sexual cannibalism, females face a trade-off between mating and consuming a courting male. Because male and prey availability can change seasonally, sexual cannibalism may change with season. However, we are not aware of any work examining how sexual cannibalism in insects relates to the time of season. Here, we examined the seasonal pattern of sexual cannibalism and reproductive behaviour in the sexually cannibalistic praying mantis (Mantis religiosa). We repeatedly collected the last instars of praying mantises from the field and brought them up under natural weather and photoperiod, but standardised feeding and socioecological conditions. After the females reached sexual maturity, we allowed all of the females to mate during two mating trials. In comparison to female praying mantises maturing later in the season, early-maturing females were larger but of poorer body condition on the day of a mating trial (20 days after the adult moult). During the first round of mating trials, early-maturing virgin females cannibalised males more frequently than their late-maturing counterparts. In contrast, late-maturing females that mated in the first round of mating trials were more likely than early-maturing, nonvirgin females to be cannibalistic in the second round of mating trials. The latency time until copulation was correlated with a risk of sexual cannibalism and was longer in early-maturing females. Our study suggests that the date of the last (adult) moult plays an important role in the occurrence of sexual cannibalism.     

Does a single meal affect female reproductive output in the sexually cannibalistic praying mantid Iris oratoria?

1. One explanation of the evolution of sexual cannibalism, the female’s consumption of a male during or following courtship or copulation, is that this behaviour increases the female’s fitness. This study tests the assumption that a single meal increases female reproductive output significantly in the sexually cannibalistic praying mantid Iris oratoria L. 2. In 38 mating trials, seven of the females cannibalised the males. In order to augment the number of females that fed, an additional nine females were each fed one cricket nymph at the end of the mating trial. 3. Three measures of female reproductive output – the occurrence of oviposition, the mass of the first ootheca, and the number of eggs in the first ootheca – increased significantly with female feeding condition, which was a reflection of food consumed before the mating trial. Females that copulated later in the season tended to lay lighter oothecae. 4. The females’ consumption of a meal during the mating trial, either a conspecific male or a cricket, did not influence any measure of reproductive output significantly, although possible effects upon subsequent oothecae cannot be ruled out. 5. If, as the present study suggests, a single meal provides a negligible or delayed benefit to female reproductive output, the evolution of sexual cannibalism might lie in alternative explanations, which include possible fitness benefits to cannibalistic females in the nymphal stage or possible paternity benefits to the cannibalised males.     

The cannibalistic behaviour of two Gammarus species (Crustacea: Amphipoda)

This study examines the cannibalistic behaviour of the freshwater amphipods Gammarus duebeni celticus Stock & Pinkster, 1970 and G. pulex (L., 1758). In the first experiment, interactions were staged among all combinations of single adult males, single adult females, adults in the precopulatory mate-guarding phase and juveniles. Cannibalism by inter-moult individuals on newly moulted conspecifics occurred in all interaction categories in both species. Gammarus d. celticus , however, were significantly more cannibalistic than G. pulex. Cannibalism between and within sex and size categories (males > females > juveniles) was facilitated by the vulnerability of individuals at moult. Individuals of smaller size categories, however, did not cannibalize newly moulted conspecifics of larger size categories. Males were less cannibalistic on newly moulted females than on newly moulted males and juveniles and, when in the precopulatory condition, appeared to defend females from cannibalistic attacks. In a second experiment, stream conditions were simulated in the laboratory and replicated populations monitored for nine weeks. High levels of cannibalism, and the species and sex differences in cannibalism identified in the first experiment, were confirmed under these heterogeneous conditions. Cannibalism by males on their newly moulted female mating partners, termed 'reversed' sexual cannibalism, was further investigated. When males were deprived of foraging opportunities, cannibalism of precopulatory partners was significantly more frequent. The occurrence of 'reversed' sexual cannibalism is thus interpreted as a conflict between motivation to feed and motivation to mate.     

Does Female Personality Determine Mate Choice Through Sexual Cannibalism?

Animal personalities (e.g. consistent across‐context behavioural differences between individuals) can lead to differences in mate choice. However, evidence for this link remains limited. Pre‐mating sexual cannibalism can be a behavioural syndrome (i.e. a suboptimal personality) in which adaptive female aggression towards heterospecific prey spills over on non‐adaptive aggression towards courting males, independently of the female mating or feeding status (i.e. the ‘aggressive spillover hypothesis’, ASH). On the other hand, sexual cannibalism can also be a form of mate choice by which females selectively kill or mate with males depending on the male phenotype. We introduce the hypothesis that the most aggressive females in the population will not only attack males more frequently, but will be less likely to impose sexual selection on males through sexual cannibalism. Assuming that in a field common garden experiment in which females were fed ad libitum the rate of weight gain by a female may reflect her voracity or aggressiveness, we show that in the cannibalistic burrowing wolf spider Lycosa hispanica (formerly L. tarantula), voracity towards heterospecific prey predicts a female's tendency towards sexual cannibalism. Unmated females with higher weight gains were more cannibalistic and attacked males regardless of the male phenotype. On the other hand, females that were less voracious tended to be less cannibalistic, and when they did kill a male, they were selective, killing males in poorer condition and mating with those in better condition. Our results demonstrate that females with different phenotypes (growth rates) differently imposed selection on male condition, tentatively supporting the hypothesis that female aggression levels can spill over on sexual selection through sexual cannibalism.     

Challenging the Aggressive Spillover Hypothesis: Is Pre‐Copulatory Sexual Cannibalism a Part of a Behavioural Syndrome?

Pre‐copulatory cannibalism – females devouring males during courtship – may bring no benefit to either sex. The ‘aggressive spillover hypothesis’ (ASH) posits that pre‐copulatory cannibalism represents a spillover of female aggressiveness from the juvenile foraging context, when aggressiveness is advantageous, to the adult mating context, when aggressiveness may be non‐adaptive or maladaptive. The ASH suggests that individuals exhibit limited plasticity in aggressive behaviours because they are genetically canalised for indiscriminate aggressiveness towards prey and conspecifics, including males. Hence, a tendency to employ pre‐copulatory cannibalism is a part of the female aggression syndrome, an assertion generally accepted in the personality field. We here re‐evaluate the previous findings in the light of personality criteria, which we propose for ASH validation: between‐individual differences, repeatability and heritability in tendency for pre‐copulatory attacks (and pre‐copulatory cannibalism) and voracity towards prey, and their correlation. To re‐evaluate ASH and to allow for additional or alternative explanations, we ask whether pre‐copulatory cannibalism depends on female hunger, mating status, size and/or male quality. Finally, we ask whether cannibalistic females have a reduced reproductive success as predicted by the ASH. While repeatability and heritability in voracity towards prey and its correlation with the tendency to engage in pre‐copulatory cannibalism were found in certain systems, we lack any evidence for repeatability and heritability in pre‐copulatory cannibalistic attempts and for its maladaptiveness. Rather than only resorting to the ASH, foraging and mate choice hypotheses may also explain pre‐copulatory cannibalism. We suggest clarifying the use of the terms sexual cannibalism (effect) and female aggressiveness or tendency to attack and devour males (cause), and argue that male strategies to avoid cannibalism should be considered. We propose testing the ASH as the explanation for pre‐copulatory cannibalism in those cases where female tendency to devour males correlates with actual pre‐copulatory cannibalism and when all the above criteria are fulfilled. Finally, we propose future directions for studying the ASH.     

Intriguing compensation by adult female spiders for food limitation experienced as juveniles

We conducted a field experiment to test for food limitation in immature stages, and its consequences for mature females, in the territorial, cannibalistic spider Lycosa tarentula (L.). Randomly selected antepenultimate juveniles were provided supplemental prey until they matured, at which time supplemental feeding ceased. Immature stages of L. tarentula are food-limited. Supplemented juvenile spiders decreased foraging activity, disappeared at a lower rate and grew faster than the control spiders, which had been exposed only to ambient prey levels. Fed juvenile females were less hungry at maturity, as judged by an index of body condition, and showed higher mating success as adults, as judged by cohabitation rates with mature males. Foraging theory predicts that in order to compensate for residual effects of food limitation, adult female spiders that had experienced a shortage of prey as juveniles – the controls – would have to exhibit a greater increase in foraging activity upon maturing than the prey-supplemented group. Contrary to expectation, the control females did not increase their foraging activity, but the previously fed females did forage more actively as adults. Furthermore, the difference in mass gain during the mating period between the two groups was opposite from what the difference in change in foraging activity would predict. Control females, the spiders that had not changed their foraging activity, gained mass more rapidly than the previously fed females, with the result that the two groups were similar in mass by the end of the mating period. We hypothesize that an increased rate of sexual cannibalism may have been one mechanism by which control females compensated for the food limitation that they had experienced as immatures.     

Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives

Mating systems are frequently shaped by conflicts over reproductive interests between males and females. Sexual cannibalism canbe an especially dramatic manifestation of such conflicts.However, the resolutions of this conflict differ among sexuallycannibalistic spider species. Cannibalism may be in the interestof both sexes when females consume males as a foraging decisionto improve fecundity and/or males sacrifice their bodies toincrease fertilization success. In other species, females exertsequential choice of partner by selectively terminating copulationthrough cannibalism while males fail to obtain a paternityadvantage. Here, we investigate the adaptive value of cannibalismin the orb-web spider Nephila plumipes where 60% of males donot survive copulation. Virgin females in poor condition aremore frequently cannibalistic and more likely to kill largemales, but the frequency of cannibalism among mated femalesis not influenced by these factors. Instead, males that matewith mated females increase their fertilization success bybeing cannibalized. Cannibalized males generally mate for longer,but longer copulations correspond with increased paternity onlyin mated females. The amount of sperm from particular malesthat a female stored was not influenced by any of the measuredvariables. The number of sperm stored was not related to paternity,nor was there any detectable reduction in sperm number afterfemales had reproduced. Our data suggest that the conflict between the sexes differs between virgin and mated females.Females should always cannibalize a male, but males only gainfrom cannibalism when mating with mated females, not when matingwith virgin females. Interestingly, the frequencies of cannibalismare not different in matings with virgin or mated females.     

Sexual cannibalism in the fishing spider and a model for the evolution of sexual cannibalism based on genetic constraints

Several hypotheses have been proposed for the evolution of sexual cannibalism by females. Newman and Elgar (1991) suggested that sexual cannibalism prior to mating by virgin female spiders may have evolved as a result of female foraging considerations. According to this model, an adult female's decision to mate or cannibalize a courting male should be based on an assessment of the male's value as a meal versus his value as a mate. The current study provides an empirical test of the assumptions and predictions of this model in the sexually cannibalistic fishing spider. Adult females were subjected to different food treatments, and exposed to adult males in the laboratory. However, only one of the assumptions of the model and none of its five predictions were upheld. We failed to find any effects of female foraging, female mating status, female size, male size or time of the season on females' behaviour towards courting males. Females behaved stereotypically, and many females were left unmated despite numerous mating opportunities. We also demonstrate costs of sexual cannibalism in a natural population. We propose that the act of sexual cannibalism in the fishing spider is non-adaptive, and develop a model for the evolution of premating sexual cannibalism in spiders based on genetic constraints. According to this hypothesis, sexual cannibalism by adult females may have evolved as an indirect result of selection for high and non-discriminate aggression during previous ontogenetic stages. Genetic covariance between different components of aggressive behaviour may constrain the degree to which (1) juvenile and adult aggression and/or (2) aggression towards conspecifics and heterospecifics can vary independently. We briefly review the support for our model, and suggest several critical tests that may be used to assess the assumptions and predictions of the model.     

Sexual cannibalism: high incidence in a natural population with benefits to females

Background

Sexual cannibalism may be a form of extreme sexual conflict in which females benefit more from feeding on males than mating with them, and males avoid aggressive, cannibalistic females in order to increase net fitness. A thorough understanding of the adaptive significance of sexual cannibalism is hindered by our ignorance of its prevalence in nature. Furthermore, there are serious doubts about the food value of males, probably because most studies that attempt to document benefits of sexual cannibalism to the female have been conducted in the laboratory with non-natural alternative prey. Thus, to understand more fully the ecology and evolution of sexual cannibalism, field experiments are needed to document the prevalence of sexual cannibalism and its benefits to females.

Methodology/Principal Findings

We conducted field experiments with the Mediterranean tarantula (Lycosa tarantula), a burrowing wolf spider, to address these issues. At natural rates of encounter with males, approximately a third of L. tarantula females cannibalized the male. The rate of sexual cannibalism increased with male availability, and females were more likely to kill and consume an approaching male if they had previously mated with another male. We show that females benefit from feeding on a male by breeding earlier, producing 30% more offspring per egg sac, and producing progeny of higher body condition. Offspring of sexually cannibalistic females dispersed earlier and were larger later in the season than spiderlings of non-cannibalistic females.

Conclusions/Significance

In nature a substantial fraction of female L. tarantula kill and consume approaching males instead of mating with them. This behaviour is more likely to occur if the female has mated previously. Cannibalistic females have higher rates of reproduction, and produce higher-quality offspring, than non-cannibalistic females. Our findings further suggest that female L. tarantula are nutrient-limited in nature and that males are high-quality prey. The results of these field experiments support the hypothesis that sexual cannibalism is adaptive to females.     

Precopulatory Sexual Cannibalism Causes Increase Egg Case Production,Hatching Success,and Female Attractiveness to Males

Precopulatory sexual cannibalism is an extreme form of sexual conflict that can entail significant costs to the cannibalized individual and a variety of costs and benefits to the cannibal itself. Characterizing these costs and benefits is fundamental to our understanding of how this behavior evolves. Using the spider Agelenopsis pennsylvanica, we tested the reproductive consequences of precopulatory sexual cannibalism by staging cannibalization events and comparing the performance of experimental cannibals against natural cannibals (i.e., those that cannibalized on their own) and non‐cannibals. We found two performance benefits associated with precopulatory sexual cannibalism: first, experimental cannibals were more likely to produce egg cases than non‐cannibals, and second, egg cases from experimental cannibals and natural cannibals were significantly more likely to hatch than those produced by non‐cannibals. We then tested whether males were more likely to approach the webs of experimental cannibals vs. non‐cannibalistic control females. Our data demonstrate that sexual cannibalism increases female attractiveness to males. Although this result seems counterintuitive, in fact, rates of precopulatory sexual cannibalism were much lower in females that had already cannibalized their first male: 38% of sexually naïve females engaged in precopulatory sexual cannibalism, whereas only 5% of females engaged in cannibalism a second time. Thus, males that approach cannibals receive two benefits: they are less likely to be cannibalized precopula, and they have the possibility of mating with females that have a higher probability of producing viable egg cases. Taken together, our data suggest that precopulatory sexual cannibalism affords females numerous benefits and may have a hand in shaping male mate choice decisions.     

Sexual cannibalism in the garden spider Araneus diadematus

In natural populations, courting males of Araneus diadematus are often consumed by females before they have successfully copulated. Despite the possible nutritional benefits of sexual cannibalism for females, the male can derive no benefit by being consumed before copulation. In this study, females that consumed a single male significantly increased their body mass, regardless of the quality of their diet. The implication is that, for A. diadematus, sexual cannibalism increases female fecundity. In experimentally controlled courtship sequences, larger males were less likely to be cannibalized than smaller males, but female size had no effect on male mating success. The mating success of males was not influenced by the age of the male, indicating that cannibalism is not the results of male senility.     

Male sexual cannibalism in a sand‐dwelling wolf spider with sex role reversal

Sexual cannibalism usually involves females attacking and consuming males before, during or after copulation. Sex role reversed systems may provide insight into the debate about whether it arises as mistaken identity, a spillover in female aggressiveness, foraging decisions, and/or extreme mate choice. In such systems, males may be selective and voracious to compensate for their higher reproductive costs, and thus males may be the sexually cannibalistic sex. Allocosa brasiliensis shows a reversal in sex roles and male‐biased sexual size dimorphism (the opposite of the common pattern in spiders). The present study aimed to test whether males cannibalize or mate according to female reproductive status or body characteristics. Each of 20 adult males was consecutively exposed to one virgin and one mated female, alternating the order of exposure. Males preferred to mate with virgin females in good body condition and heavier‐mated females. Males attacked 15% of virgins and 40% of mated females and cannibalized 10% and 25% of the total trials, respectively. The astonishing male cannibalistic behaviour best agrees with extreme mate choice hypotheses because attacks were more frequent on mated females of low body condition. This is the first report of male sexual cannibalism in a sex role reversed system. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 68–75.     

Sexual Cannibalism as a Manifestation of Sexual Conflict

Sexual cannibalism is a well-known example for sexual conflict and has many facets that determine the costs and benefits for the cannibal and the victim. Here, I focus on species in which sexual cannibalism is a general component of a mating system in which males invest maximally in mating with a single (monogyny) or two (bigyny) females. Sexual cannibalism can be a male strategy to maximize paternity and a female strategy to prevent paternity monopolization by any or a particular male. Considerable variation exists between species (1) in the potential of males to monopolize females, and (2) in the success of females in preventing monopolization by males. This opens up exciting future possibilities to investigate sexually antagonistic coevolution in a largely unstudied mating system.Sexual cannibalism, the killing and consumption of potential or actual mating partners in a mating context, has been termed a “pinnacle of sexual conflict” because of the dramatic ending of the act for one mating partner, mostly the male (Elgar and Schneider 2004). This contradiction of traditional sex roles may be one reason why the phenomenon of sexual cannibalism has intrigued naturalists for a long time. In the context of sexual conflict, sexually cannibalistic behavior of females is a harmful trait, and antagonistic traits are expected to evolve in males, which can be considered the reverse of most other examples in which females respond to male harm (see Perry and Rowe 2014). I will discuss potential antagonistic traits to sexual cannibalism in males but will also show that the above view is too simplistic when it comes to spider mating systems characterized by very low male mating rates.It is important to note that there are different kinds of sexual cannibalism based on very different evolutionary scenarios (Elgar and Schneider 2004; Prenter et al. 2006; Wilder et al. 2009). The most extreme divide exists between cannibalism before sperm transfer, which can only benefit the cannibal, and sexual cannibalism during or after sperm transfer (from here on termed postinsemination sexual cannibalism), which can benefit the cannibal and the victim (Elgar and Schneider 2004). Despite a longer history of research on preinsemination sexual cannibalism, the evolutionary causes and consequences of postinsemination sexual cannibalism are generally less debated.There are reports (often anecdotal) on the occurrence of sexual cannibalism from diverse invertebrate taxa (Elgar 1992) and it may well occur in all predatory invertebrates that are potentially cannibalistic (Polis 1981). It is beyond the scope of this brief review to list and evaluate all reported occurrences. Rather, I will start with a brief account of the generally discussed causes and consequences of sexual cannibalism and will then concentrate on the conflicting interests of the sexes regarding postinsemination sexual cannibalism in mating systems that are characterized by very low male mating rates.Studies that investigate sexual cannibalism experimentally are mostly concerned with (1) nutritional aspects, (2) the importance of sexual size dimorphism and sexual selection, and, increasingly, (3) behavioral syndromes. The aggressive spillover hypothesis suggests that preinsemination sexual cannibalism is part of a behavioral syndrome in which aggression against mating partners spills over from a foraging context (Arnqvist and Henriksson 1997). There is mixed support for this idea in the few species that have been looked at. In several spider species, females consistently differ in their aggressiveness and these differences affect sexual cannibalism (for a recent debate about the evidence for this hypothesis, see Johnson 2013; Kralj-Fišer et al. 2013b; Pruitt and Keiser 2013).A majority of studies have taken a unilateral view and have been concerned with the “motivation” of the cannibal; because sexual cannibalism generally occurs in predators, hunger is a well-supported motivation (Wilder et al. 2009). Many predators are food-limited, and, assuming a trade-off between foraging and mating, the balance may tilt toward foraging under particular circumstances (modeled by Newman and Elgar 1991). Food and mate availability will influence the costs and benefits of sexual cannibalism for females and have been one focus of a recent review on sexual cannibalism (Wilder et al. 2009).In all predatory and cannibalistic animals, mating partners impose selection on each other’s abilities to avoid or resist aggression. This selection pressure is asymmetrical if one sex is physically dominant. Indeed, the differences in size between females and males often determine the frequency of sexual cannibalism, perhaps because the potential to resist a cannibalistic attack is size-dependent (Elgar 1992; Wilder and Rypstra 2008). Usually, males are the victims and females are the cannibals. Yet, reversed sexual cannibalism has also been reported and appears to be associated with the reversed pattern in sexual size dimorphism. Examples are the water spider, Arygoneta aquatica (Schutz and Taborsky 2005, 2011) and role-reversed wolf spiders (Aisenberg et al. 2011). In the gnaphosid spider, Micaria sociabilis, large, young males cannibalize old and relatively smaller females (Sentenska and Pekar 2013). These examples further support the notion that the relative size differences of a mating pair play a part in determining the likelihood of sexual cannibalism. Patterns can be found both on a between-species comparative scale and on a within-species scale (Wilder and Rypstra 2008; Wilder et al. 2009), and they are also reported as an underlying pattern in cannibalism outside a mating context (Bleakley et al. 2013). Furthermore, there is anecdotal evidence for the same pattern in hermaphrodites (e.g., Goto and Yoshida 1985; Michiels et al. 2003), which may constitute a particularly interesting case to study, as the power asymmetries are less obviously related to the male or female role.In asymmetric encounters, the costs and risks of aggressive behavior toward potential mating partners are low for the dominant partner. Toward smaller males, females could use aggressiveness as a means of partner choice. Indeed, many studies suggest that sexual selection in addition to gaining a meal may be the adaptive value of sexual cannibalism (Prenter et al. 2006). From the female perspective, aggressive behavior directed toward males may serve as a general screening of partner quality, a mechanism often described as indirect mate choice (Elgar and Nash 1988; Prenter et al. 2006; Kralj-Fišer et al. 2012). A screening method implies that females attack every male, and suitors that cannot withstand and persist an attack will be killed and consumed; alternatively, females may differentiate between males and attack and consume only those males that do not meet certain quality criteria (reviewed in Prenter et al. 2006). The latter has been found in wolf spiders (Wilgers and Hebets 2012). The latter mechanism of direct choice is more complex than the indirect one as it requires perception and assessment of quality cues, and large enough benefits of choosiness are expected to match the costs. Mate rejection via sexual cannibalism is considered a particularly extreme case of sexual conflict mostly because rejection can lead to death. Although this may be true for the individual male that loses all future reproductive success, frequencies of preinsemination sexual cannibalism might be rather low (Kralj-Fišer et al. 2013b). Please note that in almost every species, a certain proportion of individuals will be excluded from the mating market and will have no mating success. The claim that prevention of mating success via sexual cannibalism results in more intense sexual conflict than exclusion from mating with less drastic measures has, to my knowledge, never been tested. Because of the scarcity of data on natural frequencies of preinsemination cannibalism, a meta-analysis would not reveal a realistic picture at this stage. Hence, to date, it is not feasible to compare the relative strength of selection imposed by a cannibalistic mate choice strategy against a strategy with less drastic consequences of mate rejection. More studies are needed to unravel the exact nature of sexual selection under the threat of ending as a meal. Below, I will briefly sketch possible responses to selection imposed by sexually cannibalistic females before or during insemination.     

Death feigning in the face of sexual cannibalism

Pre-copulatory sexual cannibalism by females affects male and female reproductive success in profoundly different ways, with the females benefiting from a meal and the male facing the risk of not reproducing at all. This sexual conflict predicts evolution of traits to avoid cannibalism and ensure male reproductive success. We show that males of the nuptial gift-giving spider Pisaura mirabilis display a remarkable death feigning behaviour--thanatosis--as part of the courtship prior to mating with potentially cannibalistic females. Thanatosis is a widespread anti-predator strategy; however, it is exceptional in the context of sexual selection. When the female approached a gift-displaying male, she usually showed interest in the gift but would sometimes attack the male, and at this potentially dangerous moment the male could 'drop dead'. When entering thanatosis, the male would collapse and remain completely motionless while retaining hold of the gift so it was held simultaneously by both mates. When the female initiated consumption of the gift, the male cautiously 'came to life' and initiated copulation. Death feigning males were more successful in gaining copulations, but did not have prolonged copulations. We propose that death feigning evolved as an adaptive male mating strategy in conjunction with nuptial gift giving under the risk of being victimized by females.     

Sexual cannibalism, competition, and size dimorphism in the orb-weaving spider Nephila plumipes Latreille (Araneae: Araneoidea)

The degree and direction of sexual dimorphism varies widely,but in several taxa of orb-weaving spiders, including Nephila,males may be less than one-tenth the size of females. This differenceis commonly attributed to selection through precopulation sexualcannibalism: females may either fail to detect very small males,or ignore them as potential prey items. However, there is oftenthe potential for male-male competition in these species becauseseveral males can be found on the web of a single female. Weinvestigated experimentally the effects of sexual cannibalismand male-male competition on male body size and hence sexualdimorphism in the Australian golden orb-weaver (Nephila plumipes).Small males were less likely to be detected and cannibalizedthan larger males. However, larger males excluded small malesfrom the central hub of the web, where mating takes place. Theconflicting effects of sexual cannibalism and male-male competitionmay be responsible for the relatively large variation in malebody size in this species.     

Influence of age at mating on the reproductive performance of Parthenium beetle,Zygogramma bicolorata (Coleoptera: Chrysomelidae)

Abstract Age-specific mating incidence, sexual maturation and effect of age at mating on reproductive performance of the Parthenium beetle, Zygogramma bicolorata Pallister, was studied. Based on 50% mating incidence the calculated age of sexual maturation of males and females was 10.5 and 11.1 days, respectively, which was not statistically significant. However, on the basis of age at first mating, that is, sexual maturity, females matured 2 days earlier than males. Fecundity, pre-oviposition, oviposition and post-oviposition period and female longevity appear to be influenced by female age at mating with reproductive performance peaking at 30 days. On the other hand, egg viability was influenced by male age and was highest when males mated at the age of 40 days. To summarise, egg production and timing of egg deposition was female age-dependent, whereas egg fertility was male age-dependent. It was also observed that females mated at a later age and laid a higher number of eggs immediately after mating than did earlier mated females. This was ostensibly in a bid to increase fitness by maximizing reproductive output in the reduced life span available. This is the first investigation on the effect of age of females at mating on reproduction in this beetle.     

Behavioral response of male mantid Tenodera aridifolia (Mantodea: Mantidae) to windy conditions as a female approach strategy

When sexual cannibalism presents a sexual conflict, one expects to find male traits that reduce the risk of cannibalism. In sexually cannibalistic species, selection is thought to have favored the evolution of male approach behaviors that reduce the probability that the female will kill the male. We tested the hypothesis that male mantids change their approach behavior in response to wind to reduce the risk of being noticed by females. Time between detection of the female by the male and mating was shorter under windy than windless conditions. Sexual approach behavior was observed more frequently under windy than windless conditions. Moreover, this behavior was observed more frequently when the female was walking than when the female was not walking under windy conditions. The detection rate of male mantids by females was significantly lower on swaying leaves than on fixed leaves. Our results thus indicate that male mantids were more active in response to wind. Therefore, we suggest that the male's quick approach strategy toward females when the wind is blowing at short range is adaptive in reducing the risk of detection by females.     

Sexual Cannibalism in the Brown Widow Spider (Latrodectus geometricus)

Sexual cannibalism may represent an extreme form of male monogamy. According to this view, males gain reproductive success by sacrificing themselves to females. We studied the occurrence and timing of sexual cannibalism in the brown widow spider Latrodectus geometricus and compared male courtship and mating behavior with virgin and with previously mated females. We found that events of sexual cannibalism are frequent, that they occur during copulation and that males initiate cannibalism by placing the abdomen in front of the female’s mouth‐parts during copulation (somersault behavior). Both the somersaults and mating occurred more frequently with virgins than with previously mated females. Our results support the hypothesis that sexual cannibalism is a male strategy in this species. The somersault behavior was previously known only from the redback spider, Latrodectus hasselti. It is as yet unknown whether self‐sacrifice has evolved more than once in this genus.