Virgin females compete for mates in the male lekking species Ceratitis capitata

Abstract. Aggressive behaviour occurring in intrasexual competition is an important trait for animal fitness. Although female intrasexual aggression is reported in several insect species, little is known about female competition and aggressive interactions in polygynous male lekking species. The interactions of female Mediterranean fruit flies, Ceratitis capitata (a male lekking species), with other females and mating pairs under laboratory conditions are investigated. Mature, unmated (virgin) females are aggressive against each other and against mating pairs, whereas immature females are not. Female aggression against other females decreases dramatically after mating; however, mated females maintain aggression against mating pairs. In addition, higher intrasexual aggression rates are observed for mature, virgin females than for virgin males of the same age. The results show that female aggressiveness is virginity related, suggesting female competition for mates. These findings have important implications for understanding the physiological aspects of a complex social behaviour such as aggression and should stimulate further research on female agonistic behaviour in male lekking mating systems.     

Male coercion and the costs of promiscuous mating for female chimpanzees

For reasons that are not yet clear, male aggression against females occurs frequently among primates with promiscuous mating systems. Here, we test the sexual coercion hypothesis that male aggression functions to constrain female mate choice. We use 10 years of behavioural and endocrine data from a community of wild chimpanzees (Pan troglodytes schweinfurthii) to show that sexual coercion is the probable primary function of male aggression against females. Specifically, we show that male aggression is targeted towards the most fecund females, is associated with high male mating success and is costly for the victims. Such aggression can be viewed as a counter-strategy to female attempts at paternity confusion, and a cost of multi-male mating.     

The role of female competition in the mating success of two clones of the Amazon molly, Poecilia formosa

Clones of the unisexual fish Poecilia formosa , the Amazon molly, live in the wild in association with their progenitor bisexual species, and compete with them for resources. These resources include food, space and also mates, since the Amazon molly reproduces gynogenetically, a process in which sperm transferred from a male host species activates their eggs. Earlier studies of the adaptive mechanisms that facilitate the coexistence of the bisexual and unisexual forms have focused upon male behaviour, but recent work with another unisexual species, Poeciliopsis , demonstrated that female aggressive behaviour may play an important part in determining the ecological standing of a clone.
We have extended our observations to female mating behaviour in two clones in the Amazon molly; clone 1 that does not thrive well under laboratory culture; and clone 2 that is hardy and survives very well. There was no aggression between the clones, nor did the clones show aggression towards females of the bisexual species. However, clone 1 consistently was more successful in the number of mating encounters made with the male; it approached the male more often than clone 2 and fled from the male less often. Males also showed some preference for mating with clone 1 females. If there are physiological differences in the wild clones similar to those seen in the laboratory, the mating advantage of the less robust clone 1 may ensure its continued survival in competition with a more vigorous clone.     

Mating Tactics in Response to Costs Incurred by Mating with Multiple Males in Wild Female Japanese Macaques

We investigated the costs of mating with multiple males in terms of feeding time, traveling distances, sexual proceptivity, and male aggression, for wild female (Macaca fuscata yakui) on Yakushima Island, Japan. We analyzed all-day focal sampling data from 7 females during the mating season (Sept.-Nov. 1996). On days when estrous females copulated with multiple males, they decreased their feeding time to half that of anestrous days, traveled longer distances, showed more proceptive sexual behaviors and received more aggression from subordinate males than on days when they copulated with only the 1st-ranking male. On days when females copulated with only the 1st-ranking male, they showed no difference in feeding time with that of anestrous days, and expended less effort than the above mating pattern because of short traveling distances, diminished sexual proceptivity and a lower frequency of aggression received. The results suggest that the costs of estrous vary according to female sexual proceptivity and the number and social status of mating partners. Female Japanese macaques exhibit a mixed mating strategy over prolonged estrous periods, which may provide females with opportunities to maximize the benefits of copulating with multiple males and to minimize the costs of estrus by mating with only the 1st-ranking male. During an estrous cycle, females may be adjusting efforts for reproduction and survival; i.e., mating vs. feeding.     

Male-male competition and speciation: aggression bias towards differently coloured rivals varies between stages of speciation in a Lake Victoria cichlid species complex

Sympatric speciation driven by sexual selection by female mate choice on a male trait is a much debated topic. The process is problematic because of the lack of negative frequency-dependent selection that can facilitate the invasion of a novel colour phenotype and stabilize trait polymorphism. It has recently been proposed that male-male competition for mating territories can generate frequency-dependent selection on male colouration. Rare male cichlid fish would enjoy a fitness advantage if territorial defenders bias aggression towards male cichlid fish of their own colour. We used blue (ancestral type) and red phenotypes of the Lake Victoria cichlid species complex Pundamilia. We tested the aggression bias of wild-caught territorial blue male cichlid fish from five separate populations for blue vs. red rival male cichlid fish using simulated intruder choice tests. The different populations vary in the frequency of red male cichlid fish, and in the degree of reproductive isolation between red and blue, reflecting different stages of speciation. Blue male cichlid fish from a population that lack red phenotypes biased aggression towards blue stimulus male cichlid fish. The same was found in two populations where blue and red are reproductively isolated sister species. This aggression bias may facilitate the invasion of a novel colour phenotype and species coexistence. Blue male cichlid fish from two populations where red and blue are hybridizing incipient species biased aggression towards red stimulus male cichlid fish. Thus, after a successful invasion of red, aggression bias alone is not likely to generate frequency dependence required to stabilize the coexistence of phenotypes. The findings show that aggression bias varies between stages of speciation, but is not enough to stabilize the process of speciation.     

Influence of the estrous cycle on heterosexual aggression in two strains of rats (S3 and WEzob)

Two strains of rats (S₃ and WEzob), which show different levels of aggression in the laboratory, were tested in repeated heterosexual confrontations. Daily 15-min observations were made of the interactions between a female throughout a complete estrous cycle and the same male partner. In both strains the topography of aggression was similar in males and females, but the frequency of specific parameters varied. Males showed more offensive and females more defensive patterns. The overall level of aggression was very low on the day of estrous, when the female was sexually receptive. There were no differences in any elements of female or male behavior between the other 3 days of the cycle. The results support previous conclusions from single-sex encounters that in rats there is no sexual dimorphism in the ability to show aggression.     

The Cost of Male Aggression and Polygyny in California Sea Lions (Zalophus californianus)

In polygynous mating systems, males often increase their fecundity via aggressive defense of mates and/or resources necessary for successful mating. Here we show that both male and female reproductive behavior during the breeding season (June–August) affect female fecundity, a vital rate that is an important determinant of population growth rate and viability. By using 4 years of data on behavior and demography of California sea lions (Zalophus californianus), we found that male behavior and spatial dynamics—aggression and territory size—are significantly related to female fecundity. Higher rates of male aggression and larger territory sizes were associated with lower estimates of female fecundity within the same year. Female aggression was significantly and positively related to fecundity both within the same year as the behavior was measured and in the following year. These results indicate that while male aggression and defense of territories may increase male fecundity, such interactions may cause a reduction in the overall population growth rate by lowering female fecundity. Females may attempt to offset male-related reductions in female fecundity by increasing their own aggression—perhaps to defend pups from incidental injury or mortality. Thus in polygynous mating systems, male aggression may increase male fitness at the cost of female fitness and overall population viability.     

Nonbreeding season pairing behavior and the annual cycle of testosterone in male and female downy woodpeckers, Picoides pubescens

Studies in birds show that testosterone (T) concentrations vary over the annual cycle depending on mating system and life history traits. Socially monogamous species show pairing behavior throughout the year and low levels of male-male aggression and are underrepresented in these studies, yet the function of testosterone could be particularly important for sexual and social interactions occurring outside the breeding season. We measured fecal T concentrations over the annual cycle and the frequency of interactions between male and female downy woodpeckers (Picoides pubescens) from late fall through early spring. We validated the fecal assay by collecting blood in conjunction with a subsample of our fecal samples: fecal T correlated with circulating levels in the blood. The annual peak level of T in males was relatively low and short-lived, similar to that of other bird species with low levels of male-male aggression and high paternal care. The annual cycle of female T resembled the male pattern, and the ratio of male T to female T was close to 1.0. Likewise, the frequency of aggression among females was similar to the frequency among males. Overall, testosterone levels in both sexes were variable, even in winter. In other bird species, sexual behavior during nonbreeding periods correlates with circulating levels of T in males. Based on this observation, we tested the hypothesis that T in winter was positively related to the frequency of interaction between mated downy woodpeckers. The results showed no such relationship. We discuss this finding and further relate the annual cycle of T in both males and females to behaviors that appear to facilitate mate choice and retention of the pair bond during conspecific challenge.     

Male courtship success and female discrimination in the mediterranean fruit fly (Diptera: Tephritidae)

The mating success of individually marked male Mediterranean fruit flies was monitored over 6 consecutive days in the laboratory. Mating frequency was nonrandom, as the numbers of both males that failed to mate and males that mated many (more than four) times were much higher than expected by chance alone. Differential mating success resulted in part from intermale variation in activity level. Male copulatory success was positively correlated with the numbers of courtships performed, attempted copulations (mountings), and females courted. Male-male aggression, on the other hand, and a negligible effect on male mating success. Female choice also appeared to influence male mating frequency. Fewer than 10% of courtships resulted in mating, and in most cases females terminated courtship by simply moving away from the male. Females that did mate generally selected males having higher copulatory scores than previously rejected males.     

Male-killing bacteria trigger a cycle of increasing male fatigue and female promiscuity

Sex-ratio distorters are found in numerous species and can reach high frequencies within populations. Here, we address the compelling, but poorly tested, hypothesis that the sex ratio bias caused by such elements profoundly alters their host's mating system. We compare aspects of female and male reproductive biology between island populations of the butterfly Hypolimnas bolina that show varying degrees of female bias, because of a male-killing Wolbachia infection. Contrary to expectation, female bias leads to an increase in female mating frequency, up to a point where male mating capacity becomes limiting. We show that increased female mating frequency can be explained as a facultative response to the depleted male mating resources in female biased populations. In other words, this system is one where male-killing bacteria trigger a vicious circle of increasing male fatigue and female promiscuity.     

The Payoff of Fighting in House Crickets: Motivational Asymmetry Increases Male Aggression and Mating Success

Motivational asymmetry caused by differences in subjective resource value is a key component of strategic models of aggression. We study the role of motivational asymmetry in determining differential aggression and mating success of male house crickets, Acheta domesticus. We also assess the extent to which mating differences associated with motivational asymmetry are due to direct male–male fighting vs. male–female interactions. We manipulated male motivation to compete for a mating opportunity by providing males with either no access or nightly access to females for 4 d prior to the experiment. As predicted, when males from each treatment had to compete for the female, those with lower prior access were more aggressive and mated more often. In contrast, when males from each treatment were paired individually with females, there was no significant difference in the frequencies with which they pursued, courted or mated with females. We also found no evidence for female choice based on motivational asymmetry; the rate of successful courtship did not differ between treatments. We conclude that prior mate encounter rate can generate motivational asymmetry, leading to differential mating success mediated by direct male–male aggression.     

Frequent Failure of Male Monopolization Strategies as a Cost of Female Choice in the Black Widow Spider Latrodectus tredecimguttatus

In many mating systems, males strive for securing paternity through monopolizing females. As male monopolization attempts often contradict female interests, this conflict may fuel an evolutionary arms race. In the widow spider genus Latrodectus, females are commonly polyandrous, whereas males are monogynous, hence restricted to mate with a single female, making paternity protection particularly important. Potential mating plugs (specialized embolus sclerites of male copulatory organs) have been discovered in the complex female genital tracts of several Latrodectus species. In this study, we investigated mating strategies in the Mediterranean black widow spider Latrodectus tredecimguttatus and tested the adaptive value of female attacks against male monopolization efforts. In a double mating experiment, we manipulated the number of insertions (=copulations) for first and second males to assess female behaviour and male embolus sclerite placement success. Our results indicate that first males′ embolus sclerites inside the females′ sperm stores physically block sclerites of subsequent males. While female attacks did not affect the deposition of potential mating plugs, they significantly reduced copulation duration. Irrespective of female aggression, male sclerite placement failure occurred frequently, but large males were more successful than smaller competitors. We suggest that the complex genital morphology in both sexes may have co‐evolved antagonistically and female morphology could serve to favour large males for fertilization.     

No genetic correlation between the sexes in mating frequency in the bean beetle, Callosobruchus chinensis

Female multiple mating, which is common in animals, may have evolved not in response to fitness advantages to females but as a genetic corollary to selection on males to mate frequently. This nonadaptive hypothesis assumes a genetic correlation between females and males in mating frequency, which has received a few empirical investigations. We tested this hypothesis by observing the correlated response in male mating frequency in the adzuki bean beetle, Callosobruchus chinensis to artificial selection on female propensity to remate. Compared to control females, females from lines selected for increased or decreased female propensity to remate had, respectively, higher or lower mating frequency measured by the number of mating within a given period. This indicates that female receptivity to remating is genetically correlated with female mating frequency, and thus the artificial selection for female propensity to remate influenced female mating frequency. In contrast, males from the selected lines that diverged in female mating frequency did not vary significantly in their mating frequency. These results indicate that there is no genetic correlation between the sexes in mating frequency in C. chinensis. This study shows that the reason why females in C. chinensis remate despite suffering fitness costs cannot be explained by indirect selection resulting from selection on males to mate multiple times.     

Sexual initiation in wild mountain gorillas

A field study of wild mountain gorillas was conducted to elucidate details of sexual initiation required for an interpretation of the increased frequency of copulation during the menstrual cycle, in comparison to the wild, that occurs when this species is tested in traditional laboratory pair tests. Although females in the wild played a clear role in establishing and maintaining proximity to the male and assertively presenting for copulation, all female presenting was preceded by some form of behavior by the male. Of particular relevance were several components of the male’s chest-beat display that had been observed at much higher frequencies in the laboratory tests. Although originally described as male aggression in the laboratory tests, such behavior now appears to be male sexual initiative, elicited by female proximity. The exaggerated form and frequency of the display in the laboratory, and the increased copulation during the cycle that ensued, are likely due to (1) placing females in proximity to a male daily, rather than on 2–3 days of estrus as occurs in the wild, and (2) the inability of the female in the laboratory to withdraw from male proximity during pair tests in a single cage. In addition to clarifying the data on laboratory pair tests, the data on wild gorillas have relevance to the captive breeding of gorillas.     

No detectable genetic correlation between male and female mating frequency in the stalk-eyed fly Cyrtodiopsis dalmanni

There is much interest in explaining why female insects mate multiply. Females of the stalk-eyed fly Cyrtodiopsis dalmanni can mate several times each day in a lifetime which may span several months. There are many adaptive explanations, but one hypothesis that has received little rigorous empirical attention is that female multiple mating has evolved for non-adaptive reasons as a correlated response to selection for high male mating frequency rather than because of direct or indirect benefits accruing to females. We tested this hypothesis in stalk-eyed flies by measuring the mating frequency of females from lines that exhibited a direct response in males to artificial selection for increased ('high') and decreased ('low') male mating frequency. We found that the mating frequency of high-line females did not differ from that of low-line females. Hence, there was no support for a genetic correlation between male and female mating frequency in this species. Our study suggests that the genes which influence remating may not be the same in the sexes, and that females remate frequently in this species to gain as yet unidentified benefits.     

Size-dependent sex allocation and sexual selection in Aplysia kurodai, a hermaphrodite with nonreciprocal mating

Abstract. For simultaneous hermaphrodites, a male-to-female shift in sex allocation with growth, and weak sexual selection on the male function, is predicted by many theories, although empirical data for both predictions are insufficient for internally fertilizing hermaphrodites with nonreciprocal mating. To address these issues, I studied mating and egg-laying behavior of the sea hare, Aplysia kurodai (Gastropoda: Opisthobranchia) in the laboratory. Both frequency and duration of egg laying increased with body weight, indicating that fecundity increased with weight. On the other hand, frequency and duration of mating as males did not increase with body weight, suggesting that sperm usage was independent of weight. Therefore, sex allocation shifted from male to female functions with growth. The lack of a relationship between body weight and mating activities as males also suggests that there was no "female" choice for large partners. However, the frequency of mating as females increased with body weight, suggesting "male" choice for large partners. This "male" choice is further supported by the presence of size-assortative mating and a longer duration of mating when the female partner was large. In addition, the variance in mating frequency as females was larger than that as males. As a whole, the mating behavior in A. kurodai can be summarized as choosy as males and unchoosy as females, the opposite of the patterns known in most gonochoric and hermaphroditic animals.     

Male Aggression,Female Mimicry and Female Choice in the Rove Beetle,Aleochara curtula (Coleoptera,Staphylinidae)

Causes, consequences and pheromonal regulation of male contest and female choice in the staphylinid beetle, Aleochara curtula (Goeze), have been investigated in the field and in the laboratory. At the feeding and mating site (carcass) the sex ratio is male biased. Polyandry is affected by prolonged copulations, spermatophore plugs and anti-aphrodisiac pheromones transferred from the male, and by female repulse behaviour as well. Aggression of competing males leads to expulsion of inferior males from the carcass. Young, starved and multiply mated males, which need access to the food resource, produce the female sex pheromone. They release homosexual responses, but also avoid intrasexual aggression. On the other hand, females behave aggressively towards individuals bearing the female sex pheromone or repulse their copulatory attempts. Those males of insufficient physiological condition produce a lighter spermatophore and fertilize less eggs. The adaptive significance of female mimicry, male mating tactics, and female choice is discussed.     

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

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

Aggression and Mating Success in Three Species of Drosophila1

Three closely related species of Drosophila: D. virilis, D. americana, and D. novamexicana, are known to differ in levels of male-male aggression. Through direct observation in the laboratory, we attempted to determine and characterize the relationships between intrasexual aggression and mating success in males of each of these species. Our results indicated that the most important determinant of male mating success was not the amount of aggression performed by a male, but rather the amount of aggression directed towards him.     

The Interaction of Female Condition and Mating Status on Male-Male Aggression in a Wolf Spider

Fighting behavior has been studied extensively with strong emphases on factors that independently determine winners and losers as well as how much effort an individual should invest in a given contest for a resource. Much less attention has been paid to how interacting qualities of disputed resources modulate aggression. In a laboratory study, we examined the interactive effects of female condition and mating status on dyadic male aggression in the wolf spider Pardosa milvina . We discovered that males exhibited significantly more aggressive behaviors when in the presence of virgin females in good condition and displayed lower and statistically similar levels of aggression when placed with virgin, poor condition females; mated, good condition females; mated, poor condition females; and no females. Because previous studies have suggested that virgin females alone should be highly prized because of putative first-mate sperm priority patterns, this study contributes to this body of literature by suggesting that diet history and body condition mitigate the reproductive advantages of mating with virgin females as indicated by levels of male-male aggression, but further investigation is needed.