Effects of Egg and Circulating Testosterone on Ring‐Necked Pheasant (Phasianus colchicus) Male Traits and Combat Outcome

Studies of avian species have shown that maternal effects mediated by the transfer of egg hormones can profoundly affect offspring phenotype and fitness. We previously demonstrated that the injection of a physiological amount of testosterone (T) in the eggs of ring‐necked pheasants (Phasianus colchicus) disrupted the covariation among male morphological traits at sexual maturity and positively affected male mating success. Here, we investigate whether egg T exposure affected adult male circulating T levels at the onset of the breeding season (reflecting gonadal maturation), and the relationship between circulating T and male traits. Egg T exposure did not affect pre‐mating plasma T. T levels were not associated with the expression of secondary sexual and non‐sexual traits or socio‐sexual behaviour (social rank, overall fighting ability and mating success). However, wattle brightness decreased with increasing circulating T in males hatched from T‐eggs (T‐males) but not among control males. In dyadic encounters during the peak mating period, control males with higher pre‐mating T levels had higher chances of being dominant over other control males. However, higher pre‐mating T levels did not predict success in male‐male competition in encounters involving T‐males. We suggest that the long‐term effects of egg T on male phenotype do not originate from differential gonadal maturation according to egg T treatment. Rather, prenatal androgens may have priming effects on functioning of target tissues, translating into differential phenotypic effects according to androgen exposure during embryonic development.     

Sexual behavior of male pigs

Two major characteristics of males that affect the likelihood of achieving copulation are the sexual motivation and mating competency of the male. The behavior of domestic animals, including their sexual behavior, is dependent upon a complex interaction between the organism's internal and external environment. In male pigs, as in other mammalian species, it is clear that testicular steroids are required to maintain sexual behavior and testosterone plays a critical role. Consistent with studies in other species, it is apparent in male pigs that there is a threshold circulating concentration of androgens and/or estrogens required to maintain sexual behavior and that the level of sexual motivation is unrelated to levels of sex steroids providing these are adequate for normal sexual behavior. Key aspects of the external environment that affect the sexual behavior of the male pig include genetic, seasonal, social, sexual and psychological factors.     

Sperm transfer and paternity in the scorpionfly <Emphasis Type="Italic">Panorpa cognata</Emphasis>: large variance in traits favoured by post-copulatory episodes of sexual selection

Post-copulatory episodes of sexual selection can be a powerful selective force influencing the reproductive success of males. In order to understand variation in male fertilisation success, we first need to consider the pattern of sperm utilisation by females following matings with more than one male. Second, we need to study those traits responsible for male success in sperm competition. Here we study both male sperm transfer characteristics as well as offspring paternity of females mated to two males in the scorpionfly Panorpa cognata. By repeatedly mating males to virgin females and interrupting copulation at defined time points, we found for all males that sperm transfer set off after approximately 40 min. During the remaining copulation, sperm transfer of individual males was continuous and with constant rate. Yet the rate of sperm transfer differed between individual males from about one sperm per minute to more than eight sperm per minute for the most successful males. In addition, we measured the fertilisation success in sperm competition of males with known sperm transfer capability. The relative number of sperm transferred by males during copulation, estimated from copulation duration and the males’ individual sperm transfer rate, explained a large proportion of variation in offspring paternity. The mode of sperm competition in this species, thus, conforms largely to a fair raffle following complete mixing of sperm prior to fertilisation. Hence, male differences in both the ability to copulate for long and of rapid sperm transfer will translate directly into differences in reproductive success.     

Female control of paternity in the sexually cannibalistic spider Argiope keyserlingi

Sexual conflict theory predicts an antagonistic coevolution, with each sex evolving adaptations and counter-adaptations to overcome a temporary dominance of the other sex over the control of paternity. Polyandry allows sexual selection to operate after mating has commenced, with male and female interests competing for control of fertilization. There are numerous examples of male control of paternity, but few studies have unambiguously revealed female control. Attributing variance in paternity to females is often difficult since male and female influences cannot be separated unambiguously. However, we show that polyandrous female orb-web spiders Argiope keserlingi (Arancidae) control the paternity of their offspring by adjusting the timing of sexual cannibalism. Our experiments reveal that females copulating with relatively smaller males delay sexual cannibalism, thereby prolonging the duration of copulation, and that these males consequently fertilize relatively more eggs.     

Sexual differentiation of pheromone processing: Links to male-typical mating behavior and partner preference

Phoenix et al. (Phoenix, C., Goy, R., Gerall, A., Young, W., 1959. Organizing actions of prenatally administered testosterone propionate on the tissues mediating mating behavior in the female guinea pig. Endocrinology 65, 369–382.) were the first to propose an essential role of fetal testosterone exposure in the sexual differentiation of the capacity of mammals to display male-typical mating behavior. In one experiment control male and female guinea pigs as well as females given fetal testosterone actually showed equivalent levels of mounting behavior when gonadectomized and given ovarian steroids prior to adult tests with a stimulus female. This finding is discussed in the context of a recent, high-profile paper by Kimchi et al. (Kimchi, T., Xu, J., Dulac, C., 2007. A functional circuit underlying male sexual behaviour in the female mouse brain. Nature 448, 1009–1014.) arguing that female rodents possess the circuits that control the expression of male-typical mating behavior and that their function is normally suppressed in this sex by pheromonal inputs that are processed via the vomeronasal organ (VNO)-accessory olfactory nervous system. In another Phoenix et al. experiment, significantly more mounting behavior was observed in male guinea pigs and in females given fetal testosterone than in control females following adult gonadectomy and treatment with testosterone. Literature is reviewed that attempts to link sex differences in the anatomy and function of the accessory versus the main olfactory projections to the amygdala and hypothalamus to parallel sex differences in courtship behaviors, including sex partner preference, as well as the capacity to display mounting behavior.     

Male sexual behavior does not require elevated testosterone in a lizard (Coleonyx elegans, Eublepharidae)

Male sexual behavior depends on gonadal androgens in species of all major vertebrate lineages, including reptiles. However, male sexual behavior includes distinct appetitive and consummatory phases, typically denoted as courtship and mounting, with potentially different hormonal control. Different proximate controls of courtship versus mounting could enable disconnected evolutionary losses and gains of various aspects of male sexual behavior. Male courtship display, which is activated by testosterone (T) in many species, is an ancestral trait in the lizard family Eublepharidae. However, Coleonyx elegans (Yucatan Banded Gecko) lost the courtship display, while retaining a highly simplified male sexual behavior that involves only mounting for copulation. We performed surgical manipulations (castration with and without T replacement in adult males; implantation of adult females with exogenous T) to investigate hormonal mechanisms involved in this evolutionary novelty. Our results indicate that the expression of simplified sexual behavior in C. elegans does not require elevated circulating levels of T, a finding that is previously unreported in lizards. In females, however, exogenous T induced male-like mounting. Thus, the mounting phase of sexual behavior is not activated by T in the traditional sense of this term but probably requires post-natal, maturational organization (if not periodic reorganization) by androgens. We conclude that the simplification of male sexual behavior and its independence from elevated levels of circulating androgens in C. elegans evolved via 1) evolutionary loss of the androgen-activated courtship display and 2) retention of the mounting phase, which has a longer “functional memory” for the effects of androgenic steroids.     

Do Sex Differences in the Brain Explain Sex Differences in the Hormonal Induction of Reproductive Behavior? What 25 Years of Research on the Japanese Quail Tells Us

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the sex specificity of androgens and estrogens. Androgens were thought to facilitate male-typical traits, and estrogens were thought to facilitate female-typical traits. By the mid-20th century, however, it was apparent that administering androgens to females or estrogens to males was not always effective in sex-reversing behavior and that in some cases a “female” hormone such as an estrogen could produce male-typical behavior and an androgen could induce female-typical behavior. These conceptual difficulties were resolved to a large extent by the seminal paper of C. H. Phoenix, R. W. Goy, A. A. Gerall, and W. C. Young in (1959,Endocrinology65, 369–382) that illustrated that several aspects of sexual behavior are different between males and females because the sexes have been exposed during their perinatal life to a different endocrine milieu that has irreversibly modified their response to steroids in adulthood. Phoenixet al.(1959) therefore formalized a clear dichotomy between the organizational and activational effects of sex steroid hormones. Since this paper, a substantial amount of research has been carried out in an attempt to identify the aspects of brain morphology or neurochemistry that differentiate under the embryonic/neonatal effects of steroids and are responsible for the different behavioral response of males and females to the activation by steroids in adulthood. During the past 25 years, research in behavioral neuroendocrinology has identified many sex differences in brain morphology or neurochemistry; however many of these sex differences disappear when male and female subjects are placed in similar endocrine conditions (e.g., are gonadectomized and treated with the same amount of steroids) so that these differences appear to be of an activational nature and cannot therefore explain sex differences in behavior that are still present in gonadectomized steroid-treated adults. This research has also revealed many aspects of brain morphology and chemistry that are markedly affected by steroids in adulthood and are thought to mediate the activation of behavior at the central level. It has been explicitly, or in some cases, implicitly assumed that the sexual differentiation of brain and behavior driven by early exposure to steroids concerns primarily those neuroanatomical/neurochemical characteristics that are altered by steroids in adulthood and presumably mediate the activation of behavior. Extensive efforts to identify these sexually differentiated brain characteristics over the past 20 years has only met with limited success, however. As regards reproductive behavior, in all model species that have been studied it is still impossible to identify satisfactorily brain characteristics that differentiate under early steroid action and explain the sex differences in behavioral activating effects of steroids. This problem is illustrated by research conducted on Japanese quail (Coturnix japonica), an avian model system that displays prominent sex differences in the sexual behavioral response to testosterone, and in which the endocrine mechanisms that control sexual differentiation of behavior have been clearly identified so that subjects with a fully sex-reversed behavioral phenotype can be easily produced. In this species, studies of sex differences in the neural substrate mediating the action of steroids in the brain, including the activity of the enzymes that metabolize steroids such as aromatase and the distribution of steroid hormone receptors as well as related neurotransmitter systems, did not result in a satisfactory explanation of sex differences in the behavioral effectiveness of testosterone. Possible explanations for the relative failure to identify the organized brain characteristics responsible for behavioral sex differences in the responsiveness to steroids are presented. It is argued that novel research strategies may have to be employed to successfully attack the fundamental question of the hormonal mechanisms regulating sex differences in behavior.     

The sexual behavior of Japanese monkeys

The sexual behavior of four troops of wild Japanese monkeys at Jigokudani and at Takasakiyama was observed for about one month during the middle of the breeding season. Sexual behavior was classified into 46 types from the viewpoint of sign behavior, and a catalogue of this was presented. It was shown that there was high correlation between the two most common types of behavior of the male, hindquarters-display and hand-on-back, and subsequent copulation. Seven stages were noticed in the sequence from initial encounter to leave-taking of a consort pair, and these stages were observed in a fairly regular order in the copulatory sequence. There was correlation between male positive attitude toward females and dominance rank order of the male, but was not between copulation and the dominance rank order. Adult females without infant showed and received positive sexual behavior; females who had an infant neither showed nor received the behavior; juvenile females showed but did not receive the behavior. Males showed positive sexual behavior toward females of their own group, but copulation between them was the most scarce due to female refusal.     

Adrenal contribution to the induction of sexual behavior in the female musk shrew.

Sexually experienced female musk shrews (Suncus murinus) lack an ovarian, vaginal, and behavioral estrous cycle. Females, once induced by their initial contact with a male, are able to display copulatory behavior whenever a male is present (Rissman, Silveira, and Bronson, 1988). Based on plasma levels of steroids, and on hormone replacement studies conducted after ovariectomy (OVX), we have shown that testosterone (T) plays an essential role in the regulation of female sexual behavior (Rissman and Crews, 1988; Rissman, Clendenon, and Krohmer, 1990a; Rissman, 1991). To date we have only examined the potential contribution of adrenal steroids to female sexual behavior in a preliminary manner. After adrenalectomy, gonadally intact females display significantly lower levels of sexual behavior than controls (Rissman and Bronson, 1987). The following experiments were conducted to examine the role the adrenal steroids (in contrast to the medullary hormones) play in the induction of female sexual behavior in the musk shrew. In the first experiment gonadally intact females were treated with dexamethasone (DEX) to reduce the secretion of adrenal steroids. Significantly fewer females receiving DEX demonstrated sexual behavior as compared with controls. In the second study, OVX females received T-filled Silastic implants. When DEX was administered to OVX + T females at a dose that dropped circulating T levels to those found in ovary and adrenal intact females, no effect on sexual behavior was noted. The data show that the adrenals are a behaviorally important source of T and contribute toward the hormonal control of sexual behavior in these female mammals.     

Post-castration retention of reproductive behavior and olfactory preferences in male Siberian hamsters: role of prior experience

Reproductive behavior of virtually all adult male rodents is dependent on concurrent availability of gonadal steroids. The ejaculatory reflex is incompatible with long-term absence of testicular steroids and typically disappears within 3 weeks after castration. Male Siberian hamsters are an exception to this rule; mating culminating in the ejaculatory reflex occurs as many as 6 months after castration (persistent copulation). The emergence of persistent copulation many weeks after gonadectomy is here shown not to require repeated post-castration sexual experience. Preoperative sexual experience, on the other hand, significantly increases the percent of males that copulate after gonadectomy, but is not required for the emergence of this trait in 25% of males. Castration prior to puberty prevents persistent copulation in all individuals in adulthood. Persistent copulators, unlike males that cease mating activity after castration, prefer the odors of estrous over non-estrous females when tested 4 months after castration and 7 weeks after the last mating test. Neural circuits of persistent copulators retain the ability to mediate male sex behavior and preferences for female odors in the complete absence of gonadal steroids; they are influenced by preoperative sexual experience and organizational effects of gonadal hormones at the time of puberty.     

Androgenic control of male-typical behavior,morphology and sex recognition is independent of the mode of sex determination: A case study on Lichtenfelder's gecko (Eublepharidae: Goniurosaurus lichtenfelderi)

Previous work on lizards has shown that many sexually dimorphic traits depend on testosterone (T), but the details of this control can vary among species. Here, we tested the role of T on the expression of morphological, physiological, and behavioral traits in Lichtenfelder's gecko (Goniurosaurus lichtenfelderi), from the lizard family Eublepharidae notable for interspecific variation in sexually dimorphic traits and the mode of sex determination. Experiments included three groups of males (intact control, surgically castrated, castrated with T replacement) and two groups of females (intact control, T supplemented). In males, castration caused reductions in 1) the size of hemipenes, 2) offensive aggression, 3) male sexual behavior in a neutral arena, 4) activity of precloacal glands, and 5) loss of male chemical cues for sex recognition. These reductions were not observed in castrated males with T replacement. Interestingly, castrated males performed sexual behavior in their home cages, which shows that the effect of T depends on the environmental context. Notably, tail vibration, previously reported as a courtship behavior in other eublepharids, is displayed by males of G. lichtenfelderi during interactions with conspecifics of both sexes, suggesting an evolutionary shift in the meaning of this signal. In females, T induced growth of hemipenes and male-typical courtship but did not induce precloacal pore activity, aggression, or mounting. In comparison to previous reports on Eublepharis macularius, our results indicate that effects of T do not depend on the mode of sex determination. Further, our results extend our understanding of the complexity of control of male traits and illustrate how lability in the effects of T can be a general mechanism causing evolutionary changes in the components of suites of functionally correlated traits.     

Female Copulation Calls in Guinea Baboons: Evidence for Postcopulatory Female Choice?

We tested the hypothesis that primate female copulation calls are a form of postcopulatory female choice. We collected data on female sexual swellings, sexual and agonistic behavior, copulation calls and postcopulatory behavioral interactions in a multimale-multifemale captive group of Guinea baboons over a 3-mo period. Males copulated with only a few females, and females copulated with only 1 or 2 different males in the group, suggesting a harem-like mating system similar to that of hamadryas and gelada baboons. Female copulations were most likely to occur at peak sexual swellings and male copulatory success was accounted for by dominance rank and age. Variation in female tendencies to call after copulation is best explained by the copulatory success of the male with which each female copulated the most and by the number of copulating partners. The findings are consistent with predictions that calls are likely to be associated with copulation with preferred males and the risk of sperm competition. The prediction that copulation calls increased the probability of postcopulatory mate guarding is also supported. Taken together, the findings suggest that female copulation calls may play an important role in postcopulatory sexual selection and in particular in the expression of postcopulatory female choice in primate species in which females have little opportunity to choose their mates or female mate choice is costly or both.     

Control of Female Reproduction in Drosophila: Genetic Dissection Using Gynandromorphs

The sexual behavior of Drosophila melanogaster gynandromorphs was studied to analyze the relationship between different steps in the female reproductive pathway. It was assumed that, in some gynandromorphs, certain female functions are missing because the corresponding control sites (foci) are either composed of male tissue or did not develop. A given gynandromorph can show elements of both male and female reproductive pathways. None of the steps of the female reproductive pathway appeared to be dependent on any other, in contrast to male behavior where, for example, following of females is a prerequisite for attempted copulation. By correlating each of the behaviors with the genotype of the cuticle, we confirmed previous findings that the focus for the female sex appeal is located in the abdomen, but receptivity to copulation is controlled by a site in the head. Many of the gynandromorphs did not lay eggs, presumably because either the focus controlling egg transfer from the ovaries to the uterus or the one controlling egg deposition was composed of male tissue. Many of the nonovipositing gynandromorphs laid eggs while dying or could be induced to deposit eggs after implantation of hormone-producing glands or topical application of a juvenile hormone analog. Some of the noninseminated gynandromorphs laid eggs at the rate characteristic for inseminated females, suggesting that an oviposition focus (mapping in the head region) suppresses oviposition in virgin females, but not in gynandromorphs whose focus is composed of male tissue. Some of the inseminated gynandromorphs oviposited eggs at a low rate, possibly because the focus responsible for detection of insemination could not function properly. Some of the inseminated gynandromorphs laid unfertilized eggs, revealing the importance of the focus controlling sperm release from the seminal receptacle. Foci controlling egg transfer, egg deposition and sperm release are located in the thorax, according to mosaic fate mapping results and studies on the reproductive behavior of decapitated females. The location of egg deposition in the culture vial seems to be controlled by a brain site. Sexual behavior in Drosophila does not depend on the presence (or absence) of the ovary or germ line.     

Does male secondary sexual trait size reveal fertilization efficiency in Australian Drosophila bipectinata Duda (Diptera: Drosophilidae)?

Males developing relatively large, costly sexually selected traits may be of superior body condition compared to small-ornamented males. Thus, males developing the largest secondary sexual trait in a given environment may also be able to augment their investment into ejaculate quality, and fertilize a larger proportion of a female's eggs. We tested the prediction that the degree of expression of a condition-dependent secondary sexual trait, the male sex comb, in a Cape Tribulation (northeastern Australia) population of Drosophila bipectinata Duda, reveals male ability to fertilize eggs in the absence of sperm competition. This test permitted us also to evaluate whether pre-copulatory sexual selection and fertilization efficiency might act additively to influence male reproductive success because a previous study of the same population demonstrated a positive association between comb size and copulation probability. The results obtained indicate that, although genotypes developing smaller sex combs collectively had a significantly higher rate of insemination failure compared to larger comb genotypes, the hatch rate and the number of eggs laid by females inseminated by the two genotypic categories were not statistically different. The results fail to support the prediction that comb size reveals noncompetitive fertilization efficiency of males in this Australian population.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 406–413.     

Copulatory behaviors and body condition predict post-mating female hormone concentrations, fertilization success, and primary sex ratios in Japanese quail

Environmental cues and social interactions are known to influence reproductive physiology and behavior in vertebrates. In female birds, male courtship displays can result in the growth of ovarian follicles, the production of reproductive hormones, and stimulation of oviduct development, all of which have the potential to influence maternal investment. Male Japanese quail follow a typical sequence of copulatory behaviors during a mating interaction and often force copulations with unreceptive females. We hypothesized that female Japanese quail could adjust maternal investment in response to male copulatory behaviors during a single mating interaction. We investigated the relationships between 1) male copulatory behaviors and post-mating concentrations of steroids in the female, 2) female steroid concentrations and fertilization success of inseminations and 3) female steroid concentrations and the offspring sex ratio. We found that male condition and copulatory behaviors predicted female steroid concentrations and maternal investment in eggs laid after a mating trial. The body condition of one or both mates was a significant predictor of the changes in female corticosterone and testosterone concentrations after mating, whereas specific male copulatory behaviors significantly predicted changes in female progesterone concentrations. Male and female body condition, male neck grabs and post-mating concentrations of female corticosterone, progesterone, and testosterone were all significant predictors of egg fertilization rates. Female body condition, male copulation efficiency, and female testosterone concentrations were significant predictors of offspring sex ratios. Our results show that phenotypic and behavioral characteristics of male Japanese quail modulate female steroid concentrations and result in changes in maternal investment.     

Consequences of prenatal androgen exposure for the reproductive performance of female pheasants (Phasianus colchicus)

Maternal hormones in vertebrate eggs can mediate important forms of maternal effects. However, the function of hormone transfer to the eggs is still debated, especially because long-term fitness consequences have been little studied. We investigated the effect of prenatal exposure to physiologically elevated yolk testosterone (T) levels on reproduction of female pheasants (Phasianus colchicus) in captivity. We found that females hatching from T-injected eggs (T-females) had a lower egg-laying rate than controls, and their eggs were more frequently infertile than those laid by control females. There were no effects of prenatal maternal treatment on egg size and yolk T concentration, but eggs carrying a female embryo laid by T-females had smaller yolks than eggs with a male embryo, while there was no sex difference in yolk size among the eggs laid by control females. Progeny sex ratio was unaffected by maternal treatment. These findings suggest that the transfer of high androgen levels to the eggs by the mother is constrained by complex trade-offs between direct effects on her daughters' reproduction and by trans-generational differential consequences on male and female descendants.     

Postmating sexual selection: the effects of male body size and recovery period on paternity and egg production rate in a water strider

The role of male body size in postmating sexual selection wasexplored in a semiaquatic insect, the water strider Gerris lateralis.To separate effects of male size per se from those due to numericsperm competition, male recovery period (shown here to be proportionalto ejaculate size) was manipulated independently of body sizein a factorial experiment where virgin females were mated firstwith sterile males and then with focal males. Both relativemale fertilization success and female reproductive rate were measured.The number of sperm transferred increased with male recoveryperiod, an effect that was mediated by longer copulation duration,but there were no effects of body size on ejaculate size. Neithermale size nor recovery period had any significant direct effectson male fertilization success. However, copulation durationinfluenced relative fertilization success, suggesting that malesable to transfer more sperm also achieved higher fertilizationsuccess. Females exercised cryptic female choice by modulatingtheir reproductive rate in a manner favoring large males andmales that were successful in terms of achieving high relativefertilization success. Thus, successful males gained a twofoldadvantage in postmating sexual selection. This study has important implicationsfor previous estimates of sexual selection in this group of insectsbecause pre- and postmating sexual selection will be antagonisticdue to limitations in male sperm production: males mating frequently(high mating success) will on average transfer fewer sperm ineach mating and will hence tend to fertilize fewer eggs permating (low fertilization success).     

Sperm storage and copulation duration in a sexually cannibalistic spider

Female St Andrew’s Cross spiders control copulation duration by timing sexual cannibalism and may thereby control paternity if cannibalism affects sperm transfer. We have investigated the effect of copulation duration on sperm transfer and documented sperm storage patterns when we experimentally reduced the ability of females to attack and cannibalise the male. Virgin males and females were paired and randomly allocated either to a control treatment, where females were allowed to attack and cannibalise the male during copulation, or to an experimental treatment, where females were unable to cannibalise the male. The latter was achieved by placing a paintbrush against her chelicerae during copulation. Our experimental manipulation did not affect copulation duration or sperm storage. However, the number of sperm stored by the female increased with copulation duration only if the male was cannibalised, suggesting that cannibalism increases relative paternity not only through prolonged copulation duration following a fair raffle model but also through the cannibalism act itself. Future studies should explore whether cannibalised males ejaculate more sperm or whether females selectively store the sperm of cannibalised males.     

Relatively large males lower reproductive success in female zebrafish

Females can adjust their reproductive effort in relation to their partner’s perceived fitness value. In zebrafish (Danio rerio), large males are typically preferred mating partners. However, females have been observed to reduce their reproductive output with exceptionally large males but it remains unknown whether it is due to sexual harassment or aggressive behavior to establish and maintain dominance. Here, we study the association between relative male size, sexual harassment and dominance behavior, female stress status (stress behaviors and whole-body cortisol concentration), and reproductive success during a 4 day spawning trial. We found female cortisol to correlate negatively with female body size and positively with female dominance behavior. However, male and female behavior as well as female cortisol level were not related to relative male size. Females mating with relatively large males produced more and most of their eggs during the first spawning day, while females with smaller males produced few eggs during the first day but then increased egg production. Despite females produced more eggs when mating with relatively larger males, their eggs had substantially lower fertilization rates compared to females mating with relatively smaller males. Hence, overall, the reproductive fitness was lowest when females mated with a relatively large male. These findings could help to explain the maintenance of male size variation under natural conditions.     

Safer sex with feeding females: sexual conflict in a cannibalistic spider

Mating strategies are to a large degree shaped by conflictsbetween the sexes, causing a rapid antagonistic coevolutionof traits involved in reproduction. The view that sexual cannibalismrepresents a form of sexual conflict leads to the predictionof male traits that facilitate escape from cannibalistic females.A variety of traits have been suggested to serve this functionin spiders, where sexual cannibalism is comparatively common.Empirical evidence, however, is virtually absent. Here we showexperimentally that opportunistic mating with feeding females,which has been reported from several species of orb-weavingspiders, greatly reduces the risk of cannibalism and injuryfor males in the spider Nephila fenestrata. This has directconsequences for a male's fertilization success because survivingmales can reduce the female's remating probability by guardingher against rivals. Although copulation with previously matedfemales sometimes appears to be mechanically impossible, secondmales that do copulate can expect to fertilize on average 64%of a female's eggs. Our results support the view that opportunisticmating may have evolved as a male tactic in a context of sexualconflict over sexual cannibalism.