Lifetime mating success in the damselfly Coenagrion puella

Lifetime mating success of male azure damselflies (Coenagrion puella) was measured in a natural population. The major determinant of mating success is the number of days a male spends at the breeding site, which is mostly determined by a male's adult lifespan. Long-lived males have a higher mating rate than short-lived males, and daily mating rate increases with age up to 6 days, then falls. Large males live longer, but have a lower daily mating rate than small males. These effects of size are very weak, accounting for no more than 2% of the daily variance in mating success. The only overall effect of size on lifetime mating success is that males at both extremes of the size distribution are more likely to fail to mate. Chance differences in the number of females encountered are sufficient to account for the remaining variance in mating success. The weather is also shown to have a major effect on mating success. We draw attention to the ways in which it may be misleading to draw conclusions about the action of sexual selection from studies of daily, rather than lifetime, reproductive success. We provide evidence to support the view that variance in male reproductive success is neither evidence for sexual selection, nor a measure of its intensity.     

The Effects of Perceived Mating Opportunities on Patterns of Reproductive Investment by Male Guppies

Males pay considerable reproductive costs in acquiring mates (precopulatory sexual selection) and in producing ejaculates that are effective at fertilising eggs in the presence of competing ejaculates (postcopulatory sexual selection). Given these costs, males must balance their reproductive investment in a given mating to optimise their future reproductive potential. Males are therefore expected to invest in reproduction prudently according to the likelihood of obtaining future matings. In this study we tested this prediction by determining whether male reproductive investment varies with expected future mating opportunities, which were experimentally manipulated by visually exposing male guppies (Poecilia reticulata) to high or low numbers of females in the absence of competing males. Our experiment did not reveal consistent effects of perceived future mating opportunity on either precopulatory (male mate choice and mating behaviour) or postcopulatory (sperm quality and quantity) investment. However, we did find that male size and female availability interacted to influence mating behaviour; large males visually deprived of females during the treatment phase became more choosy and showed greater interest in their preferred female than those given continuous visual access to females. Overall, our results suggest males tailor pre- rather than postcopulatory traits according to local female availability, but critically, these effects depend on male size.     

Sexual selection on male body size and mating behaviour in American toads,Bufo americanus

Mating behaviour of B. americanus was observed from 1985 to 1987. The population contained 38–45 males and 11–26 females, depending on the year. The breeding season of this ‘explosive breeder’ usually encompassed less than 48 h. Male reproductive success varied from zero to two matings per season and zero to an estimated 15 126 zygotes per season. All females mated once per season and variation in their zygote production was estimated to be 4017–11 624 zygotes per season. Body length explained 76% of the variation in zygote production of females. However, male body length was only weakly correlated with mating success in two of three seasons, and with zygote production in one of three seasons. Male arm length was predicted to correlate with male mating success because longer arms should facilitate remaining clasped to females when challenged by rival males. However, mating males did not differ from non-mating males in arm length, and the relationship between arm length and body length was the same for the sexes. Various male behaviours were measured using focal-animal sampling but only call rate correlated with male mating success. The pattern of size dimorphism (females larger than males) is consistent with the observed sex-specific relationships between reproductive success and body size.     

Male Seminal Fluid Substances Affect Sperm Competition Success and Female Reproductive Behavior in a Seed Beetle

Male seminal fluid proteins are known to affect female reproductive behavior and physiology by reducing mating receptivity and by increasing egg production rates. Such substances are also though to increase the competitive fertilization success of males, but the empirical foundation for this tenet is restricted. Here, we examined the effects of injections of size-fractioned protein extracts from male reproductive organs on both male competitive fertilization success (i.e., P2 in double mating experiments) and female reproduction in the seed beetle Callosobruchus maculatus. We found that extracts of male seminal vesicles and ejaculatory ducts increased competitive fertilization success when males mated with females 1 day after the females’ initial mating, while extracts from accessory glands and testes increased competitive fertilization success when males mated with females 2 days after the females’ initial mating. Moreover, different size fractions of seminal fluid proteins had distinct and partly antagonistic effects on male competitive fertilization success. Collectively, our experiments show that several different seminal fluid proteins, deriving from different parts in the male reproductive tract and of different molecular weight, affect male competitive fertilization success in C. maculatus. Our results highlight the diverse effects of seminal fluid proteins and show that the function of such proteins can be contingent upon female mating status. We also document effects of different size fractions on female mating receptivity and egg laying rates, which can serve as a basis for future efforts to identify the molecular identity of seminal fluid proteins and their function in this model species.     

TErritorial defence and mating success in males of the small heath butterfly, coenonympha pamphilus L. (Lepidoptera: Satyridae)

It has long been recognized that territorial defence in male butterflies must be some sort of mating strategy and that the territories are used as mating stations. However, so far, no systematic study has established the adaptive significance of territorial behaviour. This study is an attempt to fill this gap. By comparing the distribution of territories with the distribution of locations where wild and released virgin females mated this study shows that, in the small heath butterfly (Coenonympha pamphilus), males in territories have higher mating success than males outside territories. This supported the hypotheses that the function of territorial behaviour is to secure more matings and that the territories are mating stations. Wing length measurements suggest the same. Large males residing in territories tended to mate more often than small males, which were usually found outside territories. Since resident males were larger than non-resident males, this size difference was used to see how territorial occupancy influenced longevity. Mark-recapture of measured males revealed no significant correlation between wing length and the further life expectancy of males, strongly suggesting that the mating success of males in territories is also higher when measured over their whole lifetime.     

Callers and satellites in the natterjack toad: evolutionarily stable decision rules

Male natterjack toads, Bufo calamita, sometimes called to attract females and sometimes behaved as silent satellites, attempting to intercept females attracted by callers. Small males with low intensity calls most frequently adopted the satellite tactic and preferred to parasitize the loudest callers. Because body size and call intensity were highly correlated with male mating success, small males with weak calls were at a reproductive disadvantage, and probably achieved greater success by exploiting the displays of larger, louder males than by calling themselves. The behaviour adopted by individual males in a given situation was predicted by a game theory model which assumed that males used an evolutionarily stable decision rule when choosing between alternative mating tactics. However, the model provided close agreement with observed behaviour only when it assumed that males have imperfect information about the behaviour of competitors. It is concluded that male toads adopt a conditional strategy which depends on their attractiveness to females. By switching between mating tactics appropriately, males maximized expected mating success within the constraint of the information available to them. The decision rule of the model qualitatively corresponds to a proximate mechanism that males appeared to use when switching between tactics. The model offers insights into the behaviour of other species in which males display in groups to attract females.     

Lifetime mating success of males in a natural population of the papilionid butterfly,Atrophaneura alcinous (Lepidoptera: Papilionidae)

Lifetime mating success of males in a natural population of the papilionid butterfly, Atrophaneura alcinous, was investigated and causes of the variation were examined. The most successful males mated with 5 females, whereas about 73% of the males failed to mate. Body size of males was not correlated with their eclosion date, longevity and lifetime mating success. There was no trade-off between mating success and longevity, and long-lived males had a disproportionately high mating success. Although number of available females per male per day was not variable among males with different longevities, long-lived males had higher mating efficiency. Time interval between matings by non-virgin males was shorter than that from eclosion to the first mating. High lifetime mating success of long-lived males was strongly related to their mating experience, not to their age per se.     

The sex lives of parasites: Investigating the mating system and mechanisms of sexual selection of the human pathogen Schistosoma mansoni

The mating systems of internal parasites are inherently difficult to investigate although they have important implications for the evolutionary biology of the species, disease epidemiology, and are important considerations for control measures. Using parentage analyses, three topics concerning the mating biology of Schistosoma mansoni were investigated: the number of mates per adult male and female, variance in reproductive success among individuals, and the potential role for sexual selection on male body size and also mate choice for genetically dissimilar individuals. Results indicated that schistosomes were mostly monogamous, and evidence of only one mate change occurred over a period of 5-6 weeks. One male was polygynous and contained two females in its gynecophoral canal although offspring were only detected for one of the females. Even though they were primarily monogamous and the sex ratio near even, reproductive success was highly variable, indicating a potential role for sexual selection. Male body size was positively related to reproductive success, consistent with sexual selection via male-male competition and female choice for large males. However, relatedness of pairs was not associated with their reproductive success. Finally, genetically identical individuals differed significantly in their reproductive output and identical males in their body size, indicating important partner and environmental effects on these traits.     

Calling,Courtship, and Condition in the Fall Field Cricket,Gryllus pennsylvanicus

Theoretically, sexual signals should provide honest information about mating benefits and many sexually reproducing species use honest signals when signalling to potential mates. Male crickets produce two types of acoustic mating signals: a long-distance mate attraction call and a short-range courtship call. We tested whether wild-caught fall field cricket (Gryllus pennsylvanicus) males in high condition (high residual mass or large body size) produce higher effort calls (in support of the honest signalling hypothesis). We also tested an alternative hypothesis, whether low condition males produce higher effort calls (in support of the terminal investment hypothesis). Several components of long-distance mate attraction calls honestly reflected male body size, with larger males producing louder mate attraction calls at lower carrier frequencies. Long-distance mate attraction chirp rate dishonestly signalled body size, with small males producing faster chirp rates. Short-range courtship calls dishonestly reflected male residual mass, as chirp rate and pulse rate were best explained by a curvilinear function of residual mass. By producing long-distance mate attraction calls and courtship calls with similar or higher effort compared to high condition males, low condition males (low residual mass or small body size) may increase their effort in current reproductive success at the expense of their future reproductive success, suggesting that not all sexual signals are honest.     

Female choice and male reproductive success in the angel blenny,Coralliozetus angelica (Teleostei: Chaenopsidae)

Correlates of reproductive success of male Coralliozetus angelica were studied in field populations in the central Gulf of California by collecting males with their shelters (vacant barnacle tests) and counting the number of eggs defended. Male body size was positively correlated with the number of eggs defended. This apparently resulted from female preference for large males since females preferred to mate with the larger of two males in laboratory choice experiments. Condition of males, as assessed by their relative head width, was also positively correlated with the number of eggs defended. Fit of males in their shelter entrance, male colour intensity, and male size relative to immediately surrounding males were not correlated with reproductive success. The quality of shelters was an important determinant of male reproductive success since females apparently avoided mating with males in heavily fouled shelters. Large shelters tended to be more heavily fouled than small shelters and male size and shelter size were positively correlated. The resulting negative correlation of male size and shelter quality apparently constrained female preference for large males and may be an important factor limiting the degree of polygyny in this species.     

Vibratory courtship in a web-building spider: signalling quality or stimulating the female?

Courtship behaviour in spiders in the form of premating vibrations by males may function (1) as a male identity signal used for species recognition, (2) in suppression of female aggressiveness, (3) to stimulate female mating behaviour, or (4) as a quality signal used in female choice. We investigated the function of web vibration by male Stegodyphus lineatus in a series of experiments. Regardless of vibratory performance, all males mated successfully with virgin females but only 56.4% of males mated with nonvirgin females. Vibratory performance did not influence male mating success, but heavier males had a higher probability of mating with mated females. Males vibrated less often and produced fewer vibrations when introduced on the web of a mated female. Males that vibrated webs of virgin females mated faster than nonvibrating males, but there was no effect of vibration rate or body mass. There was no effect of male vibratory effort or vibration rate on female reproductive success measured as time to egg laying, clutch size, number of hatched young, number of dispersed young and offspring body mass after a single mating. Males vibrated on abandoned virgin female webs but the response decreased with increasing duration of female absence, suggesting that females produce a web-borne pheromone, which elicits male vibrating behaviour. Mated females were less receptive and not stimulated by male vibrating behaviour. We conclude that male premating vibrations in S. lineatus do not function as a male quality signal selected via female choice. Rather, the primary function of this behaviour may be to stimulate a receptive female to mate. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Spacing pattern in a social group of stray cats: effects on male reproductive success

Reproductive consequences of male spacing patterns have received relatively little attention in nonterritorial mammals, in particular in group-living species, where most studies have focused on the relation between social rank and reproductive success. We investigated the effects of spacing pattern on male reproductive success within a social, nonterritorial, promiscuous population of stray cats, Felis catus. Male home ranges overlapped home ranges of many females, consistent with a promiscuous mating system. Furthermore, males with the largest home ranges included the most female home ranges; they successfully reproduced with these females and had the highest reproductive success. Home range size predicted male reproductive success even when controlling for the effect of social rank. However, males also reproduced with females whose home range did not overlap their home range, suggesting that males can make quick excursions outside their home range to find new mating opportunities. We conclude that, in group-living situations, a male's ability to maintain a large home range may be one of the principal causes of variation in mating success in the stray cat.     

Harm to females increases with male body size in Drosophila melanogaster

Previous studies indicate that female Drosophila melanogaster are harmed by their mates through copulation. Here, we demonstrate that the harm that males inflict upon females increases with male size. Specifically, both the lifespan and egg-production rate of females decreased significantly as an increasing function of the body size of their mates. Consequently, females mating with larger males had lower lifetime fitness. The detrimental effect of male size on female longevity was not mediated by male effects on female fecundity, egg-production rate or female-remating behaviour. Similarly, the influence of male size on female lifetime fecundity was independent of the male-size effect on female longevity. There was no relationship between female size and female resistance to male harm. Thus, although increasing male body size is known to enhance male mating success, it has a detrimental effect on the direct fitness of their mates. Our results indicate that this harm is a pleiotropic effect of some other selected function and not an adaptation. To the extent that females prefer to mate with larger males, this choice is harmful, a pattern that is consistent with the theory of sexually antagonistic coevolution.     

The Role of Sexual Selection and Conflict in Mediating Among-Population Variation in Mating Strategies and Sexually Dimorphic Traits in Sepsis punctum

The black scavenger fly Sepsis punctum exhibits striking among-population variation in the direction and magnitude of sexual size dimorphism, modification to the male forelimb and pre-copulatory behaviour. In some populations, male-biased sexual size dimorphism is observed; in other, less dimorphic, populations males court prior to mating. Such variation in reproductive traits is of interest to evolutionary biologists because it has the potential to limit gene flow among populations, contributing to speciation. Here, we investigate whether large male body size and modified forefemur are associated with higher male mating success within populations, whether these traits are associated with higher mating success among populations, and if these traits carry viability costs that could constrain their response to sexual selection. Flies from five distinct populations were reared at high or low food, generating high and low quality males. The expression of body size, forelimb morphology and courtship rate were each greater at high food, but high food males experienced higher mating success or reduced latency to first copulation in only one of the populations. Among populations, overall mating success increased with the degree of male-bias in overall body size and forelimb modification, suggesting that these traits have evolved as a means of increasing male mating rate. The increased mating success observed in large-male populations raises the question of why variation in magnitude of dimorphism persists among populations. One reason may be that costs of producing a large size constrain the evolution of ever-larger males. We found no evidence that juvenile mortality under food stress was greater for large-male populations, but development time was considerably longer and may represent an important constraint in an ephemeral and competitive growth environment.     

Mating behaviour and male mating success in the green treefrog

Green treefrogs, Hyla cinerea, at a study site in eastern Georgia behaved as prolonged breeders: there were many more males present each night than females, the arrival of which was unpredictable. Individual males were usually consistent in their behaviour during a single night, and were most often observed calling. There was a weak, negative correlation between male size (snout-vent length, unless otherwise stated) and the frequency of satellite behaviour, defined as a non-calling male's being situated near a calling male. In 2 of 3 years, the mean size of males observed as satellites was less than that of the calling males with which they were associated on a given night; however, many satellites were the same size or larger than calling males. The distributions of matings per male during three seasons were not significantly different than Poisson distributions with the same means. Individual mating success was best predicted by attendance at the breeding site; mating success was negatively related to the frequency of satellite behaviour in some analyses, but very little of the variance was explained. An exhaustive series of analyses failed to show any pattern of size-dependent mating, including weight-assortative mating, even when males that were frequently satellites were excluded. The relative sizes of males and females in amplexus had little effect on fertilization success. On a seasonal basis, males were clumped in their spatial distribution, and matings tended to occur where male density was highest. Individual males were highly variable in their patterns of movement, which were not correlated with size or mating success. Mating success was also unrelated to the frequency (Hz) of the low-frequency spectral peak in the advertisement call of the male; male size and weight were negatively correlated with the frequency of the low-frequency peak.     

A selective trade-off for territoriality and non-territoriality in the polymorphic damselfly Mnais costalis

Males of the damselfly Mnais costalis occur as territorial orange-winged 'fighter' males or non-territorial clear-winged 'sneaker' males. Their morph life histories differ considerably but the estimated lifetime reproductive success is the same for the two morphs. In this study we compared the developmental and reproductive costs associated with the two morphs. Orange-winged male and female reproductive costs resulted in a decline in adult fat reserves with increasing age. In contrast, the fat reserves of clear-winged males remained constant with adult age. Body size was positively correlated with mating success in orange-winged males, but had no influence on the mating success of clear-winged males. The orange-winged male flight muscle ratios (FMRs) were significantly higher than the clear-winged male and female FMRs. However, there was no difference in the size-corrected fat reserves of the two morphs; both had higher fat reserves than females. The gain in mass between eclosion and reproduction in orange-winged males and females was almost double the mass gained by clear-winged males, suggesting that clear-winged male development is less costly. An experiment in which pre-reproductive levels of nutrition were manipulated confirmed this.     

Determinants and long‐term costs of early reproduction in males of a long‐lived polygynous mammal

In long‐lived polygynous species, male reproductive success is often monopolized by a few mature dominant individuals. Young males are generally too small to be dominant and may employ alternative tactics; however, little is known about the determinants of reproductive success for young males. Understanding the causes and consequences of variability in early reproductive success may be crucial to assess the strength of sexual selection and possible long‐term trade‐offs among life‐history traits. Selective pressures driven by fluctuating environmental conditions may depend on age class. We evaluated the determinants of reproduction in male bighorn sheep (Ovis canadensis) aged 2–4 years using 30 years of individual‐level data. These young males cannot defend estrous ewes and use alternative mating tactics. We also investigated how the age of first detected reproduction was correlated to lifetime reproductive success and longevity. We found that reproductive success of males aged 3 years was positively correlated to body mass, to the proportion of males aged 2–4 years in the competitor pool, and to the number of females available per adult male. These results suggest that reproductive success depends on both competitive ability and population age–sex structure. None of these variables, however, had significant effects on the reproductive success of males aged 2 or 4 years. Known reproduction before the age of five increased lifetime reproductive success but decreased longevity, suggesting a long‐term survival cost of early reproduction. Our analyses reveal that both individual‐level phenotypic and population‐level demographic variables influence reproductive success by young males and provide a rare assessment of fitness trade‐offs in wild polygynous males.     

Male-male competition and mating success in the orb-web spider,Nephila clavata,with reference to temporal factors

Seasonal occurrence patterns of adults of both sexes, intensity of male-male interactions, and mating success in the spider,Nephila clavata, were examined in the field. Adult males began to attend female webs about 2 weeks before female maturation. Large adult males were abundant in the early breeding season, but small males increased later in the season. From the distribution of males among female webs and size relationship of males within a web, male-male interactions seemed to be more intense when most females were still subadult. This was verified by a field experiment in which males were artificially introduced to female webs that were attended by other males. It was found that the probability of introduced males remaining on subadult female webs was lower than that on adult webs. As mating occurred mostly in the period shortly after the female final molt and first male sperm precedence was known in all spiders reported so far, intense male-male competition on subadult female webs seemed to be reasonable. Male longevity had an important influence on the mating success of males with just-molted females. Mating success was also affected by the relative body size of males present in a given period. Since larger males occupied the position closest to females within a web and stayed there longer, relative body size appeared to influence mating success through male-male competition. Female body size at maturation declined with time; hence, males that attained sexual maturity earlier had the advantage of mating with larger and more fecund females. Therefore, early maturation as well as larger size seem to be two important trairs influencing the reproductive success of males.     

Influence of male competition on male mating behaviour in the cave molly, Poecilia mexicana

In many species, male mating behaviour is correlated with male body size, with large males often being preferred by females. Small surface-dwelling Poecilia mexicana males compensate for this disadvantage by being more sexually active and using sneaky copulations. In a cave-dwelling population, however, small males do not show this behaviour. Do small males alter their behaviour in the presence of a large rival? Here, we investigated the influence of male competition on male mating behaviour in the cave form. Two males of different sizes were mated with a female either alone or together with the other male. No aggressive interactions were observed between either fish. There was no statistically significant difference in the frequency of sexual behaviours between the two treatments. In both treatments, large males were more sexually active than small males. Thus, small cave molly males do not switch to an alternative mating behaviour in the presence of a larger rival. Possibly, the extreme environmental conditions in the cave (e.g. low oxygen content and high levels of hydrogen sulphide) favour saving energetic costs, resulting in the absence of alternative mating behaviour in small males.     

Impact of body reserves on energy expenditure, water flux, and mating success in breeding male northern elephant seals

In capital breeders, individual differences in body size and condition can impact mating effort and success. In addition to the collateral advantages of large body size in competition, large nutrient reserves may offer advantages in endurance rivalry and enable the high rates of energy expenditure associated with mating success. We examined the impacts of body reserves and dominance rank on energy expenditure, water flux, mating success, and breeding tenure in the adult male northern elephant seal, a polygynous, capital breeder. Adult males expended energy at a rate of 159 ± 49 MJ d (-1), which is equivalent to 3.1 times the standard metabolic rate predicted by Kleiber's equation. Despite high rates of energy expenditure and a long fasting duration, males spared lean tissue effectively, deriving a mean of 7% of their metabolism from protein catabolism. Body composition had a strong impact on the ability to spare lean tissue during breeding. When controlling for body size, energy expenditure, depletion of blubber reserves, and water efflux were significantly greater in alpha males than in subordinate males. Large body size was associated with increased reproductive effort, tenure on shore, dominance rank, and reproductive success. Terrestrial locomotion and topography appeared to strongly influence energy expenditure. Comparisons with conspecific females suggest greater total seasonal reproductive effort in male northern elephant seals when controlling for the effects of body mass. In polygynous capital breeding systems, male effort may be strongly influenced by physiological state and exceed that of females.