Male genital length and mating status differentially affect mating behaviour in an earwig

Phenotypic variation in male genitalia may affect copulation behaviour, which can have important fitness consequences for males. Male genitalia commonly possess traits that increase male control over copulation, but in species where females control mating, a poor functional understanding often prevents insight into the processes responsible for such effects. Here, I investigate the effect of male genital length on copulation behaviour in the earwig Euborellia brunneri, where both sexes exhibit extremely elongated genitalia that correspond in shape. This model system is particularly suitable because pairs mate repeatedly and females can limit both the number and duration of copulations. I used both virgin and mated males and females in a double-mating design because longer male genitalia confer benefits in sperm competition. Consistent with a greater predicted male mating effort in mated females, the duration of individual copulations increased, but this traded off against mating frequency as cumulative mating duration remained unchanged. In contrast, male genital length increased both individual and cumulative mating duration, regardless of mating status. This difference suggests that, while males may modify copulation duration in response to mating status, females facultatively adjust mating frequency to prevent mating excessively or express preferences for increased male genital length. Notably, this study demonstrates that male genital phenotypes that are successful in sperm competition also enjoy female-mediated mating benefits.     

Repeatable female preferences, mating order and mating success in the poeciliid fish, Heterandria formosa

Sexual selection via female choice can afford preferred males comparably higher mating success than those males that lack preferred traits. In addition, many models of sexual selection assume that both male traits and female preferences are heritable. In this study we test whether females of the poeciliid fish, Heterandria formosa, have repeatable pre-copulatory preferences for larger males. We also test whether female pre-copulatory preferences are always reliable indicators of male mating success. When given a choice between a large and a small male, females prefer larger males, and the repeatability of this preference is high. Although there are no overall differences in male mating success between large and small males, large males have a higher mating success when they are the first to mate than when they are the second to mate. Likewise, preferred males also have higher mating success when they are the first to mate than when they mate second. Therefore, the repeatable female preferences observed in this study only predict male mating success when the preferred male mates first. These results illustrate that even significantly repeatable female preferences do not translate into male mating success, which is an assumption of many examinations of the importance of female choice in sexual selection.     

Male size,mating success,and mating strategy in the mosquitofish Gambusia affinis (Poeciliidae)

Summary In laboratory choice experiments, receptive female western mosquitofish Gambusia affinis affinis (deprived of contact with males 30 days) preferred the larger of two males. When two males differing in size were placed with a receptive female, the larger was generally able to monopolize access to her, but not when the female was not receptive. In other experiments, a single male was placed with a receptive or non-receptive female. These experiments showed size-correlated differences in male mating behavior. Smaller males were more likely to chase non-receptive females and attempt to inseminate them forcibly, while larger males continued to court females even if they were non-receptive. Even when the female was receptive, there was some evidence of size-correlated differences in levels of courtship and chasing.     

Male care and mating effort among Hadza foragers

Paternal care figures prominently in many scenarios of human evolution. Recently, however, such scenarios have been challenged on two scores. First, the level of male contribution may be insignificant. Second, male care may be provided as a form of mating effort, rather than parenting effort. In theory, since men can enhance their Darwinian fitness both by providing care to their own offspring if this raises offspring fitness and by pursuing additional mates if this leads to additional offspring, men should respond to payoffs from both mating and parenting effort. If men respond to payoffs from parenting effort, paternity ought to make a difference. And if men respond to payoffs from mating effort, mating opportunities ought to make a difference. I analyzed the impact of these two factors on variation in male care among the Hadza, a foraging society in Tanzania. Two predictions were tested: (1) biological children will receive more care than stepchildren, and (2) men will provide less care to their biological children as their mating opportunities increase. Both predictions were supported. These results suggest men provide care, in part, as parenting effort, and that they trade off parenting effort for mating effort when they have greater mating opportunities. Received: 21 January 1998 / Received in revised form: 24 January 1999 / Accepted: 1 February 1999     

Spatial organization and mating system of Microtus townsendii

Summary Space use by individual Townsend's voles, Microtus townsendii, was investigated in spring and summer by means of radiotelemetry and intensive live trapping in undisturbed grasslands near Vancouver, British Columbia. Home ranges of males were larger than those of females; females had significantly larger ranges in spring than in summer. Most males and females maintained territories free of individuals of the same sex in spring. Male-female pairs had their exclusive territories closely overlapping each other. The 1:1 operational sex ratio and the spatial association of pairs of males and females suggest that the voles were monogamous in the spring of 1988 and that 50% of the males were monogamous in the spring of 1989. In summer, there was more intrasexual overlap between home ranges of males and females and female ranges were considerably smaller than those of males. Females were more philopatric than males and females thought to be members of the same family group lived adjacent to each other or had overlapping home ranges. Males overlapped with more than one female in summer, but most females still overlapped with only one male, which suggests that the mating system is polygynous in summer. Thirty-five percent of the philopatric females became pregnant for the first time when the male spatially associated with their mother in the spring was still alive and thus could potentially have mated with their fathers. Male and female territoriality in spring is the proximate mechanism for the limitation of breeding density by spacing behaviour.[/p] Offprint requests to: C.J. Krebs     

Costs of courtship and mating in a sexually cannibalistic orb-web spider: female mating strategies and their consequences for males

The costs of courtship and mating may include increased risks of predation, the transmission of pathogens, and a loss of foraging opportunities. Thus, a female's decision to tolerate a courting male will depend upon how these costs offset the benefits of mating, which will depend on her reproductive and nutritional status. While these costs may be similar for mated and unmated females, the benefits of mating will be less for mated than virgin females. However, the cost of lost foraging opportunities may be higher for females with fewer nutritional reserves necessary for forming eggs. We examined how these costs and benefits influence the courtship and mating behaviour of male and female orb-web spiders, Argiope keyserlingi. In the field, females on webs that also contained a courting male intercepted fewer prey items per hour than females on webs without a male. In the laboratory, the presence of a courting male at the hub also attracted mantid predators to the web, increasing the risk of predation for both male and female. Staged mating experiments in the laboratory revealed that the frequency of female attacks and pre-copulatory cannibalism was greater among mated than virgin females. Feeding history did not affect aggression in virgin females but, among mated females, food-deprived spiders attacked and cannibalized males more frequently than sated females and only the latter ever remated. These differences in female behaviour influenced male mating strategies. Choice experiments demonstrated that males preferred to venture onto the silk threads of virgin rather than those of mated females. Similar patterns of mate selectivity were observed in the field; females with narrow abdomens attracted more males to the webs than females with broad abdomens, and copulations were observed more frequently among females with narrow abdomens. These smaller females are likely to be virgins that have recently molted. Males that preferentially mate with virgin females will not only avoid potentially fatal attacks but also obtain, on average, a higher fertilization success.     

Availability of receptive females at the mating place and mating chances of males in the dragonfly Aeschna cyanea

Summary The females of the dragonfly Aeschna cyanea visiting ponds vary in their receptiveness to males waiting there. Individual males pay several short visits to a mating place in the course of a day, searching for receptive females. Non-receptive females prefer to oviposit at the pond in the evening, whereas receptive females arrive throughout the day. The highest number of receptive females is found on warm days during the afternoon at which time the greatest number of copulations occur. However, as the number of males and, therefore, the competition between males is also highest during these periods, the mating chances of a particular male are constant throughout the day.     

Breeding synchrony and extra-pair mating in red-winged blackbirds

Using data from a 6-year paternity study of red-winged blackbirds, I tested the hypotheses that increased nesting synchrony should either promote extra-pair mating by increasing the advantage of extra-pair mating to females, or decrease extra-pair mating by constraining males from seeking extra-pair copulations. Contrary to these hypotheses, the occurrence of extra-pair paternity did not vary with nesting synchrony over the breeding season, or vary with the number of synchronous nests within territories or within marshes, or with nesting order on territories. However, for nearly all nests with extra-pair young, there were fewer females synchronous with that nest on the cuckolder's territory than on the territory of the cuckolded male. This “advantage” of a synchrony difference was less pronounced for older males that cuckolded younger males, particularly when the two males were not neighbors. Collectively, these results suggest that breeding synchrony affects extra-pair mating by affecting mate guarding, but that breeding synchrony alone can not be used to predict which females are more likely to engage in extra-pair mating, nor with which extra-pair males they will mate. Understanding why extra-pair mating by older males is less affected by breeding synchrony may explain much about both the proximate and ultimate causes of extra-pair mating in red-winged blackbirds. Received: 7 June 1996 / Accepted after revision: 25 November 1996     

Costing reproduction: effects of mating opportunity on mating success in male Bicyclus anynana butterflies

It is frequently assumed that males have an almost unlimited reproductive capacity, while access to receptive females is typically limiting. Consequently, sexual selection is expected to favor vigorous courtship behavior in males. If such behavior is associated with non-trivial costs, ample current mating opportunities should be accompanied by a reduction in future mating vigor. To test this hypothesis, three treatments differing in sex ratio were established using the tropical butterfly Bicyclus anynana: 50 males each were housed either with 0, 25, or 50 females. Mating trials involving the competition among males from each treatment for a single virgin female were carried out on days 3, 9, and 15 after allocation to treatments. While there was no difference on day 3, prior mating opportunity clearly reduced mating success on days 9 and 15, being lowest if identical numbers of males and females were housed together. This finding suggests accumulating costs associated with high courtship and/or mating activity. Further, older males were more active and initiated copulation earlier than the younger ones, consistent with the residual reproductive value hypothesis. We found no evidence for a survival or fertility cost of mating.     

Polyandrous mating in treetops: how male competition and female choice interact to determine an unusual carnivore mating system

The diversity of mammalian mating systems is primarily shaped by sex-specific reproductive strategies. In the present study, we explored determinants and consequences of a unique mating system exhibited by fossas (Cryptoprocta ferox), the largest Malagasy carnivore, where females mate polyandrously on traditional mating trees, and males exhibit intrasexual size dimorphism. Males face both contest and scramble competition, and inter-sexual size dimorphism can be pronounced, but its magnitude depends on the male morph. Using a continuous behavioral observation of six estrous females over 4 years, we investigated correlates of male contest competition and female choice based on 316 copulations. Furthermore, we assessed correlates of male scramble competition based on testes size and movement data obtained from GPS tracking. We found that females dominated males regardless of their smaller size and that females actively solicited copulations. Heavy males had highest mating success during the female’s peak mating activity, but were discriminated against afterwards. Female choice and male–male competition thus converged to generate a mating advantage for heavier males. Our results suggest that females actively seek polyandrous matings, presumably for indirect genetic benefits. Since body mass is the major determinant of male mating success and is at the same time dependent on the degree of sociality and associated hunting mode of the respective male morph, a male’s feeding ecology is likely to influence its reproductive tactic. A combination of benefits from female polyandry and the consequences of different subsistence strategies may thus ultimately explain this unusual mating system.     

Risk trading in mating behavior: forgoing anti-predator responses reduces the likelihood of missing terminal mating opportunities

Life history theory predicts that organisms make certain adjustments to their current and future reproductive effort such that fitness is maximized. Moreover, these adjustments may be fine tuned in response to risks of attack by natural enemies. Thus, we may predict that as an organism ages it will accept increasing levels of exposure to predators during mating activities, effectively trading the risk of losing terminal mating opportunities for the risk of predation. We tested this prediction in an acoustic moth, Achroia grisella, in which females orient toward and evaluate males based on their ultrasonic calling song, and both sexes may be vulnerable to predation by insectivorous bats while in flight as well as on the substrate. In the latter situation, singing males and orienting females show silence and arrestment responses, respectively, when presented with synthetic bat echolocation signals broadcast above a threshold amplitude. We found that both males and females become less sensitive to these broadcasts over the course of their brief reproductive periods, 7 and 5 days, respectively. Over the same periods, sensitivity to male song in both males and females remains constant, and relatively little senescence in sexual behavior is observed. These results support the risk trading hypothesis, and they indicate that life history principles may apply over a very short lifespan.     

Male mating effort in a polygynous ungulate

Survival and mating success are key fitness components of mammalian males. Because energy is limited, life history theory predicts trade-offs between current and future reproduction. While many studies have examined fitness trade-off in females, we know little about trade-offs faced by males. In polygynous species, male mating success is largely dependent upon intrasexual competition. Consequently, males have greater uncertainty over the benefits of a given allocation than over its costs, and the correlation between mating effort and success is likely much weaker in males than in females. We analyzed 14 years of data on the mating effort and survival of marked bighorn rams to investigate fitness trade-offs. Dominant rams defended single estrous ewes (“tending”) while subordinates attempted to copulate after separating the tending pair (“coursing”). We estimated the participation in tending and coursing for each ram and the effort in searching for breeding opportunities by each ram each year. We compared these three behavioral indices of male mating effort to demographic parameters, individual characteristics, and both yearly and long-term survival. Mating effort during the rut was unrelated to ram overwinter survival, but longevity was positively correlated with mating effort between 2 and 5 years of age. Persistent variation among rams is likely to explain this pattern, suggesting that in natural populations a few high quality males enjoy both high mating success and high survival.An erratum to this article can be found at     

Bateman gradients in a promiscuous mating system

The Bateman gradient is increasingly used to measure sexual selection and characterize mating systems. In a landmark paper, Arnold and Duvall (Am Nat 143:317–348, 1994) formulated predictions about the relationships between sex-specific Bateman gradients and the major types of mating system. In promiscuous species, gradients are expected to be strong and similar in both sexes. Current support for this prediction however remains equivocal as reported male gradients are almost constantly steeper than female gradients. Here, we estimated Bateman gradients in a wild population of Eastern chipmunks (Tamias striatus) over two reproductive seasons characterized by extreme levels of promiscuity and unbiased operational sex ratios. We found significant and positive Bateman gradients for both sexes. The gradients were not different among sexes suggesting that the strength of sexual selection was similar for males and females. The opportunity for selection was also particularly strong for a promiscuous species and not different among sexes. Our results thus support the predicted Bateman gradients for a promiscuous mating system.