Female choice of large males in the treefrog Hyla ebraccata

The mating behaviour and male mating success of Hyla ebraccata were examined over three study periods. Mated males were larger than unmated males on a significant number of nights and for one of the three study periods. In field observations of pair formation, female behaviour was consistent with choice of large males: females moved freely through the chorus, remaining within 10 cm of males larger than the nightly mean, before the male initiated amplexus. In 27% (n = 3) of these observations, males chased and fought over the female. However, the females removed two of these three males from amplexus, suggesting that females can also exercise choice after amplexus. There was a significant negative correlation between male size and dominant frequency of the primary note, indicating that the male's advertisement call contained size-related information. Comparisons of the size of mated and unmated males suggest that two factors may have affected the degree to which female choice influenced male mating success. First, the distance between calling males may have limited the opportunity for females to express a mating preference. Secondly, an increase in mean and a decrease in the variance of male size in one of the three study periods also may have limited the ability of females to express a preference for large males.     

Operational sex ratio and resource defence as predictors of the mating system in European bitterling

Operational sex ratio (OSR), the ratio of sexually active males to fertilizable females in a population, plays a central role in the theory of mating systems by predicting that the intensity of male–male competition and the degree of sexual selection increases as the OSR becomes increasingly male biased. At high values of OSR, however, resource defence theory predicts the breakdown of territoriality and a shift towards scramble competition with a decrease in sexual selection. The direction that correlations between OSR and resource competition and variance in mating success will take depends on the biology of the species of interest. We investigated the effects of male population density and male‐biased operational sex ratio on male mating tactics shown by a freshwater fish, the European bitterling, Rhodeus sericeus . This species spawns inside living unioneid mussels. Large males defended territories, were aggressive towards conspecifics under equal sex ratios and monopolized pair spawnings with females. The mating tactic, however, changed at high male density where large males ceased to be territorial and instead competed with groups of smaller males to release sperm when females spawned. This change in male behaviour from pair to group spawning has two ramifications for sexual selection. The intensity of sexual selection and variance in male mating success decrease, and the form of sexual competition changes from resource‐ to sperm competition. Thus, the use of alternative mating tactics renders the OSR unable to predict the direction of resource competition and variance in male mating success at high densities.     

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.     

Conflict over multiple-partner mating between males and females of the polygynandrous common lizards

The optimal number of mate partners for females rarely coincides with that for males, leading to a potential sexual conflict over multiple-partner mating. This suggests that the population sex ratio may affect multiple-partner mating and thus multiple paternity. We investigate the relationship between multiple paternity and the population sex ratio in the polygynandrous common lizard (Lacerta vivipara). In six populations the adult sex ratio was biased toward males, and in another six populations the adult sex ratio was biased toward females, the latter corresponding to the average adult sex ratio encountered in natural populations. In males the frequency and the degree of polygyny were lower in male-biased populations, as expected if competition among males determines polygyny. In females the frequency of polyandry was not different between treatments, and polyandrous females produced larger clutches, suggesting that polyandry might be adaptive. However, in male-biased populations females suffered from reduced reproductive success compared to female-biased populations, and the number of mate partners increased with female body size in polyandrous females. Polyandrous females of male-biased populations showed disproportionately more mating scars, indicating that polyandrous females of male-biased populations had more interactions with males and suggesting that the degree of multiple paternity is controlled by male sexual harassment. Our results thus imply that polyandry may be hierarchically controlled, with females controlling when to mate with multiple partners and male sexual harassment being a proximate determinant of the degree of multiple paternity. The results are also consistent with a sexual conflict in which male behaviors are harmful to females.     

Seasonal variation of reproductive success under female philopatry and male-biased dispersal in a common vole population

Variation of reproductive success, an important determinant of the opportunity for sexual selection, is an outcome of competition within one sex for mating with members of the other sex. In promiscuous species, males typically compete for access to females, and their reproductive strategies are strongly related to the spatial distribution of females. I used 10 microsatellite loci and the mtDNA control region to determine seasonal differences in the reproductive success of males and females of the common vole (Microtus arvalis), one of the most numerous mammals in Europe. The sex-related spatial structure and bias in dispersal between genders were also assessed. Standardized variance of the reproductive success of females did not vary seasonally due to the continuity of female philopatry throughout the breeding season and to the constancy of the number of females reproducing successfully in each season. The males are the dispersing sex, undergoing both natal and breeding dispersal. Their standardized variance of reproductive success was significantly higher than that for females in July, when only two males monopolized 80% of the females in the population and when variance of male reproductive success was highest (I_m = 7.70). The seasonally varying and high standardized variance of male reproductive success may be explained by male-male competition for matings, coupled with seasonal changes in the age structure of the population.     

Genetic evidence for the mating system and reproductive success of black sea bream (Acanthopagrus schlegelii)

Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N_b) was 33, and the N_b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N_b contributes to the maintenance of genetic diversity in farmed black sea bream populations.     

Crowd control: sex ratio affects sexually selected cuticular hydrocarbons in male Drosophila serrata

Although it is advantageous for males to express costly sexually selected signals when females are present, they may also benefit from suppressing these signals to avoid costly interactions with rival males. Cuticular chemical profiles frequently function as insect sexual signals; however, few studies have asked whether males alter these signals in response to their social environment. In Drosophila serrata, an Australian fly, there is sexual selection for a multivariate combination of male cuticular hydrocarbons (CHCs). Here, we show that the ratio of females to males that an adult male experiences has a strong effect on his CHC expression, with female‐biased adult sex ratios eliciting greater expression of CHC profiles associated with higher male mating success. Classical models predict that male reproductive investment should be highest when there is a small but nonzero number of rivals, but we found that males expressed the most attractive combination of CHCs when there were no rivals. We found that male CHCs were highly sensitive to adult sex ratio, with males expressing higher values of CHC profiles associated with greater mating success as the ratio of females to males increased. Moreover, sex ratio has a stronger effect on male CHC expression than adult density. Finally, we explore whether sex ratio affects the variance among a group of males in their CHC expression, as might be expected if individuals respond differently to a given social environment, but find little effect. Our results reveal that subtle differences in social environment can induce plasticity in male chemical signal expression.     

Constrained sex allocation in a parasitoid due to variation in male quality

The theory of constrained sex allocation posits that when a fraction of females in a haplodiploid population go unmated and thus produce only male offspring, mated females will evolve to lay a female-biased sex ratio. I examined evidence for constrained sex ratio evolution in the parasitic hymenopteran Uscana semifumipennis. Mated females in the laboratory produced more female-biased sex ratios than the sex ratio of adults hatching from field-collected eggs, consistent with constrained sex allocation theory. However, the male with whom a female mated affected her offspring sex ratio, even when sperm was successfully transferred, suggesting that constrained sex ratios can occur even in populations where all females succeed in mating. A positive relationship between sex ratio and fecundity indicates that females may become sperm-limited. Variation among males occurred even at low fecundity, however, suggesting that other factors may also be involved. Further, a quantitative genetic experiment found significant additive genetic variance in the population for the sex ratio of offspring produced by females. This has only rarely been demonstrated in a natural population of parasitoids, but is a necessary condition for sex ratio evolution. Finally, matings with larger males produced more female-biased offspring sex-ratios, suggesting positive selection on male size. Because the great majority of parasitic hymenoptera are monandrous, the finding of natural variation among males in their capacity to fertilize offspring, even after mating successfully, suggests that females may often be constrained in the sex allocation by inadequate number or quality of sperm transferred.     

Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.     

THE COSTS OF CHANGING SEX AND THE ONTOGENY OF MALES UNDER CONTEST COMPETITION FOR MATES

In its simplest form, the size-advantage hypothesis predicts that individuals should change sex in order to increase their reproductive success. In terms of lifetime expectations, this must be true for the hypothesis to hold. However, as we review here, some loss of reproductive success may occur immediately after sex change. Unavoidable costs (e.g., those resulting from a restructuring of the gonad) have not been adequately distinguished from adaptive allocations of resources which diminish current reproduction in favor of large increases in future mating success. This strategy can become particularly important for species in which a few males monopolize matings. To illustrate this idea, we describe the changes in mating frequency as mature females become sexually active males in three species of protogynous wrasses. In one species, a male defends a permanent, all-purpose territory composed of up to 12 females. When he is removed, a single female changes sex and successfully completes mating sequences with all females in the territory within an average of 5.6 days. This duration roughly corresponds to the time required for functional transformation of gonads; thus, individuals in this species suffer few reproductive losses as a result of changing sex. The largest males in two other species mate with an average of 25 to 50 females per day, but only by successfully defending reproductive territories. In one of those species, individuals that changed sex mated infrequently over a two-year period after sexual transformation and, by the end of the study, were still well below the average size of males that consistently obtained territories. Sex-changed individuals in the other species had very low reproductive success for up to 45% of the maximum lifespan as a male. It is improbable that the substantial cost of changing sex in the latter two species results from gonad restructuring or from mistakes due to imprecise cues for sex change. Instead, the cost appears to represent an investment in growth rather than current reproduction as a means of rapidly attaining a size advantage when individuals face intense competition for extraordinarily successful mating territories.     

Male mating success and female mate choice in the river sculpin,Cottus nozawae (Cottidae)

Synopsis Mating success of males and its correlates were investigated in a natural population of the polygynous fluvial sculpinCottus nozawae. Furthermore, the female mate preference of this species was examined experimentally under alternative conditions for mating in a stream. The mating success of individual males (the number of females with which a male mated) ranged between 0 and 8 with a mean of 2.41 in 1983 and 2.52 in 1989, in a population of which the sex ratio was about 1 : 2 in both years, skewed toward females. Mainly due to the excess of nests without egg masses and the few nests with one egg mass, the distribution of male mating success did not fit a Poisson distribution, indicating its non-randomness. Male mating success was not correlated either with the size of the nest rocks or with the male size, suggesting that these two variables are not determinants of mating success. The mate choice experiments demonstrated that females of this species more frequently chose smaller males as mates whose nests already contained eggs than large males without eggs. Additionally, an analysis of stomach contents of guarding males suggested that the parental males ate their own eggs during egg guarding (filial-cannibalism). Based on these results and on a comparison of reproductive characteristics with congeneric species, it is suggested that one of the most important determinants for female mate choice inCottus species may be whether or not parental males are filial egg cannibals.     

An experimental analysis of mate choice in the wren: a monomorphic, polygynous passerine

Male wrens (Troglodytes troglodytes) construct nests that areused in their display to females. Previous work has suggestedthat the number of vacant nests may be used as a mate choicecue. Correlational data from 1992 confirmed that females appearedto be assessing die number of vacant nests on a male's territoryand preferentially mating with males with more nests. Male taillengdi was also correlated widi mating success. In 1993 thenumbers of nests on territories was experimentally manipulated,the female setdement patterns confirmed that die number of vacantnests did mediate mate choice. Male tail length failed to explainadditional variance in mating success when die variance explainedby the experimental manipulation was removed, suggesting diatdie original correlation arose because both tail length andmating success were correlated widi a confounding variable.The structure of the vegetation in a male's territory influencedmating success. This appeared to be due to nests surviving betterin territories widi dense vegetation. Males on territories inwhich nests survive well had longer tails. Male-male competitionfor good territories may explain die observed effects of malemorphology on mating success. Furdier analysis of die nest choicedata showed diat all nests had an equal chance of being usedby a female. The fact diat all nests had an equal probabilityof being chosen by a female means diat each additional nestbuilt by a male wren results in die same increase in matingsuccess. This suggests diat die benefits to males of nest buildingincrease linearly. The number of nests on a territory will beaffected by various factors such as predation pressure, nestbuilding rate, and vegetation structure. The information diatfemales are getting by assessing such a signal is discussed.     

Testing the adaptive significance of sex‐specific mating tactics in collared lizards (Crotaphytus collaris)

We tested whether territorial defence is adaptive in male collared lizards by examining the extent to which territory owners monopolize females. We also tested whether females benefit by mating with multiple males using alternative tactics when local sex ratios varied. Surprisingly, neither the number of offspring that males sired, nor the number of females that males mated with varied as a consequence of highly variable local sex ratios. Moreover, both the number of offspring sired and the number of female mates were independent of male social status. Courtship frequency was under positive directional sexual selection for mating success for territorial males. None of the phenotypic traits that we examined were targets of sexual selection in nonterritorial males. Although offspring survivorship decreased with the degree of multiple mating, females mated multiply with similar numbers of territorial and nonterritorial males during all three seasons. Females did not obtain material or genetic benefits that balanced the apparent offspring survival cost imposed by mating with multiple males. Instead, females appeared to be ‘making the best of a bad job’, perhaps because the abundance of hiding places used by subordinate males makes it difficult for females to avoid male harassment. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 423–436.     

Influence of fluctuation in the operational sex ratio to mating of troop and non-troop male Japanese macaques for four years on Kinkazan Island, Japan

Taking advantage of a marked yearly fluctuation in the number of estrous females, I studied the differences in mating success between troop males and non-troop males in an unprovisioned group of Japanese macaques. Fluctuation in the defendability of estrous females by troop males, as predicted by the operational sex ratio (the number of estrous females per troop male), strongly affected the mating with ejaculation (successful mating) per observation day of both troop and non-troop males. When operational sex ratio was low, troop males monopolized successful mating inside the troop. No successful mating of non-troop males was observed inside the troop. In contrast, both troop and non-troop males were able to mate often inside the troop when operational sex ratio was high. These findings suggest that troop males obtained the benefit of secured successful mating in the troop because troop males could mate successfully even in mating seasons with a low operational sex ratio, and the chance of successful mating for non-troop males will increase as the ability of troop males to monopolize estrous females decreases.     

Behavioural aspects of the raccoon mating system: determinants of consortship success

We monitored raccoons Procyon lotor, in southern Texas during the 1990-1992 mating seasons to describe mating behaviour and identify factors affecting consortship success. During most of this study, raccoons were spatially aggregated, with female home ranges congregated around permanent water sources and larger home ranges of male groups encompassing each female group. Consortship success varied among males and ranged from zero to six females per male within a mating season. Individual females consorted with one to four different males during an oestrous period; however, most (62%) females consorted with only one male during their oestrus. Dominance through overt conflict appeared to influence male consortship success. During two mating seasons, one male from each group consorted with females on more days than all other males combined. Body weight of males was positively correlated with number of consortship days. As synchrony of oestrus increased, variance in number of consortship days among males decreased, and access to oestrous females increased for subordinate males. Wounding among males increased during the mating season, and was more frequent for males than for females. The mating system, as determined by consortship behaviour, appeared to shift between polygyny and promiscuity, and possibly varied annually as a result of the timing of oestrous cycles. Copyright 1999 The Association for the Study of Animal Behaviour.     

Postcopulatory female choice increases the fertilization success of novel males in the field cricket, Gryllus vocalis

Although recent studies have demonstrated that female crickets prefer novel males to previous mates, the relative contribution of pre- and postcopulatory behaviors to this advantage remain unknown, as do the reproductive consequences to males. I paired females either with previous or novel mates, and recorded the latency to mating and the time after mating at which the female removed the male's spermatophore, terminating sperm transfer. Females that mated with familiar males removed their spermatophores sooner than females that mated with novel males. Females paired with novel males also mated more quickly than females paired with familiar males, but this difference was not statistically significant. A molecular-based paternity analysis was used to determine whether the postcopulatory preference of females for novel males influences a male's fertilization success. Females were assigned to either mate three times with the same male and then once with a novel male, or four times with four different males. The paternity of the last male was higher when the female previously had mated repeatedly with the same male than when she had mated previously with different males. These results suggest that female spermatophore removal behavior influences male paternity such that novel males receive a fertility benefit.     

Females prefer mating males in the carmine triplefin,Axoclinus carminalis,a paternal brood-guarder

Synopsis This study investigates the role of male mating status in female choice patterns in the carmine triplefin, Axoclinus carminalis, a tripterygiid fish that exhibits paternal care. The distribution of daily reproductive activity is clumped, with many males receiving no mates and some receiving three or more. Females in this species do not prefer larger males, and characteristics of the oviposition site appear to have minimal effects on male mating success. When a female is removed from a male early in the daily spawning period, that male attracts fewer additional females for the remainder of the spawning period than does a control male. These changes in mating success are temporary, and do not affect mating success on subsequent days. A preference for mating males or males that are guarding eggs could provide asymmetric benefits for males to defend oviposition sites. This preference for males with eggs could be acting alone or with other factors such as high variance in oviposition site quality to favor the evolution of paternal care in fishes.     

Costs of Mate Guarding and Opportunistic Mating Among Wild Male Japanese Macaques

A trade-off relationship between mating and feeding effort is important when considering reproductive strategies of long-lived species. I compared the influence of male sexual activities, female mate-choice behaviors and the daily activity budget on male mating success among males in a group of wild Japanese macaques (Macaca fuscata yakui) on Yakushima Island. The 1st-ranking male, which had immigrated into the troop at this rank, more frequently approached peri-ovulatory females, spent more time grooming peri-ovulatory females and in mounting series and spent less time feeding than subordinate males did. The 1st-ranking male attained the highest mating success as a result of his high expenditure of time and energy in sexual behaviors directed toward peri-ovulatory females. Mating success of subordinate males did not relate to the amount of sexual effort, but instead to the frequency of female approaches, female rush toward males and the number of peri-ovulatory females within the group. The pattern of intermale competition shifted from nearly contest competition to scramble competition as the number of peri-ovulatory females in the group increased. Feeding time of subordinate males did not vary between the days when they copulated and the days when they did not. The findings demonstrate that mate guarding in the 1st-ranking male is a high-cost mating tactic, while opportunistic mating in subordinate males is a low-cost mating tactic. The differences in male mating tactics are probably related to male life history and to the formation of groups with a high socionomic sex ratio.     

Males Benefit from Mating with Outbred Females in Drosophila littoralis: Male Choice for Female Genetic Quality?

The evolution and expression of mate choice behaviour in either sex depends on the sex‐specific combination of mating costs, benefits of choice and constraints on choice. If the benefits of choice are larger for one sex, we would expect that sex to be choosier, assuming that the mating costs and constraints on choice are equal between sexes. Because deliberate inbreeding is a powerful genetic method for experimental manipulation of the quality of study organisms, we tested the effects of both male and female inbreeding on egg and offspring production in Drosophila littoralis. Female inbreeding significantly reduced offspring production (mostly due to lower egg‐to‐adult viability), whereas male inbreeding did not affect offspring production (despite a slight effect of paternal inbreeding on egg‐to‐adult viability). As inbreeding depressed female quality more than male quality, the benefits of mate choice were larger for males than for females. In mate choice experiments, inbreeding did not affect male mating success (measured as a probability to be accepted as a mate in a large group), suggesting that females did not discriminate among inbred and outbred males. In contrast, female mating success was affected by inbreeding, with outbred females having higher mating success than inbred females. This result was not explained by lower activity of inbred females. Our results show that D. littoralis males benefit from mating with outbred females of high genetic quality and suggest adaptive male mate choice for female genetic quality in this species. Thus, patterns of mating success in mate choice trials mirrored the benefits of choice: the sex that benefited more from choice (i.e. males) was more choosy.