Socio-sexual factors of troop fission in wild Japanese monkeys (Macaca fuscata yakui) on Yakushima Island,Japan

The troop fissions which occurred in a wild population of Japanese monkeys (Macaca fuscata yakui) were observed from 1977 to 1979 on Yakushima Island. The fissions were initiated in the breeding season by non-troop males who established a consort relation with estrous females. In order to analyze the socio-sexual factors which accelerated the fissions, the male emigrations and immigrations before and after two successive fissions, and the copulation frequencies, competition among males and preferences of mating partners in both sexes in the 1977–78 breeding season after the first fission were examined. The results indicated that three factors (a large number of non-troop males, a shortage of troop males and the females' choice of mating partners) effectively influenced on the establishment of consort relationships between non-troop males and estrous females. It is suggested that these factors may exert different effects on the troop disorganization in relation to troop size. In small-sized troops, a large number of non-troop males and a shortage of troop males may lead to stronger competition between them, and the females' choice affected by prolonged intimate relations with the dominant TMs may reduce their priority of access to estrous females. This situation possibly stimulates fission or male emigration in small-sized troops under the natural conditions on Yakushima Island. In contrast, in large-sized troops under isolated conditions, a surplus rather than a shortage of troop males may contribute to troop disorganization, as most former studies have suggested. A higher socionomic sex ratio may decrease the mating activities of subordinate troop males and increase the competition among them. This situation possibly accelerates the fission of large-sized troops through prolonged interactions between females and subordinate or peripheral troop males. A lower ratio and the females' choice, however, raise the mating chances of subordinate troop males and may not promote the fission of large-sized troops under isolated conditions. This study was financed in part by a Grant-in-Aid for Special Project Research on Biological Aspects of Optimal Strategy and Social Structure from the Japan Ministry of Education, Science and Culture, and by the Cooperative Research Fund of the Primate Research Institute, Kyoto University.     

Affiliative relations among male Japanese macaques (Macaca fuscata yakui) within and outside a troop on Yakushima Island

Male Japanese macaques (Macaca fuscata yakui) in a troop on Yakushima Island frequently groom other males. However, previous studies have not compared the social relations of troop males to those of non-troop males. I followed all troop males and non-troop males in and near a troop during a mating season and during the following non-mating season and recorded their neighbors, grooming, and agonistic interactions. Comparisons of the social relations of troop males and non-troop males with other troop members revealed that grooming and agonistic interactions with females during the mating season were similar between troop and non-troop males. However, troop males groomed each other more often and had fewer agonistic interactions among themselves than did non-troop males. Compared to what occurred in the mating season, troop males groomed females less often and exchanged grooming bouts more often with other troop males during the non-mating season. One non-troop male groomed females more frequently than did any troop male in both seasons, and this male groomed troop males more frequently than did any troop male in the non-mating season. This male immigrated into the troop during the following mating season. Regardless of their competition with respect to reproduction, male Japanese macaques on Yakushima Island maintain affiliative relations, probably to cooperatively defend fertile females from non-troop males.     

Social interactions among adult male langurs (Presbytis entellus) at Rajaji Wildlife Sanctuary

A population of langurs (Presbytis entellus)at the Rajaji Wildlife Sanctuary in northern India was investigated for 1820 hr throughout a 10-month period in 1978. Data were collected from four bisexual troops and the adult males that ranged outside of bisexual troops. Most (60%) of the observation hours occurred with a main study troop from which social and ecological data were collected. The langur population at Rajaji shows pronounced birth and mating seasons. The population density is high (ca. 80/km ²), with about 75% of the adult males living outside of bisexual troops, which typically are large and multimale. Males outside of bisexual troops occur in small all-male bands or as isolates. Relations between bisexual troops and all-male bands are characterized by relatively low levels of aggression, and members of all-male bands are able to associate with bisexual troops for prolonged periods during the mating season. As a result of these associations, nontroop males are about as successful as troop males in achieving reproductive access to troop females. These associations between bisexual troops and all-male bands occurred with a minimal amount of agonistic behavior and without mortality or injury to troop females or immatures.     

Long-term territoriality and mate acquisition in the lefteye flounder Engyprosopon grandisquama

Reproductive ecology and function of long-term territoriality in the lefteye flounder Engyprosopon grandisquama were investigated in the southwest of Kyushu Island, Japan. Field observations of marked individuals and monthly sampling suggested that the spawning season was from June to September with a peak in June–July. During the spawning season, males maintained their mating territories, although spawning behavior was not observed in August–September. Some males stayed until the next spawning season and then acquired more mates than newly appearing males, most of which could not acquire mates. Long-term retention of territory may be more advantageous for establishing a mating territory and acquiring mates in the next spawning season.     

Sociological study on the troop fission of wild

During the period from June to July 1983, the Hanyama-A troop of wild non-provisioned Japanese monkeys on Yakushima Island began to show signs of troop fission. Adult females together with their infants and juveniles subdivided into two groups, the Hanyama-K group and Hanyama-M group. After the subdivision, all of the troop males were observed vacillating between these two female groups. During the mating season, non-troop males were also observed moving around the two female groups. After this mating season, one of these non-troop males was found to have entered and become the alpha male in one of the groups, while higher-ranking adult males of the original troop settled into the other group. Each fissioned group was strongly considered to be composed of either high-ranking matrilines or low-ranking matrilines as observed previously in provisioned troops. The dominance relation between the two fissioned groups indicated that dominance rank reversal between these two female kin groups must have occurred during the course of subdivision of the troop. However, different from most previous cases of troop fission, there was no indication that males ever participated in the subdivision of the original female group. This was disrupted not as a result of males' involvement, but only as a result of antagonism among females, which initiated the troop fission. The main factor which appeared to determine when and in which fission group males eventually settled was the competition between the troop males' coalition and non-troop males and their ability to monopolize females. The present process of troop fission suggests a dual strategy between males and females (Wrangham, 1979, 1980) even in the society of Japanese macaques.     

Reproductive behavior of free-ranging Lemur catta at Beza Mahafaly Special Reserve,Madagascar

Observations of reproductive behavior in free-ranging Lemur catta were carried out during one annual cycle. Variability in the behavior of female ringtailed lemurs during parturition appears to be mainly a function of the female's parity and thus her experience. Females within a troop show estrous asynchrony and characteristically mate with more than one male. Females also exhibit proceptive behavior toward and mate with some males from other troops and with transferring males. The potential for a male to monopolize mating opportunities during a female's short estrous period is therefore limited. Male mating strategies in ringtailed lemurs can be seen as adaptations to female mate choice during a highly restricted breeding season. In this species the dominance hierarchy does not break down with regard to the order of mating. The highest ranking male (central male) mates first and shows precopulatory guarding and longer postejaculatory guarding, which may increase his chances of siring the offspring. Subsequent mating partners have developed various counterstrategies to mitigate mating order effects.     

Seasonal Variation in Mate Choice of Photinus ignitus Fireflies

Mate choice by either sex may vary with changes in the associated costs and benefits, determined by factors such as the availability of potential mates and variation in mate quality. We examined seasonal variation in operational sex ratio, courtship behavior, spermatophore mass, egg count, and the relationship between morphological traits and mating success in Photinus ignitus fireflies to determine if mate choice in either sex varied with the availability and relative reproductive investment of fertilizable females and sexually active males. Successfully mating males had larger lanterns than unsuccessful males when the operational sex ratio was male‐biased. In addition, female responsiveness to male signals increased as the number of courting males decreased, and male spermatophore mass decreased with body size across the mating season. Successfully mating females had larger body mass than unsuccessful females. Female body mass predicted egg count and female rejection by males increased as the season progressed and female size decreased. These results suggest that both male and female P. ignitus exhibit mate choice, and that such choice is influenced by seasonal variation in the abundance and quality of potential mates.     

Role of Contests in the Scramble Competition Mating System of a Leaf Beetle

Male competition for mates can occur through contests or a scramble to locate females. We examined the significance of contests for mates in the leaf beetle Chrysomela aeneicollis, which experiences a short breeding season. During peak mating season, 18–52% of beetles are found in male-female pairs, and nearly half of these are copulating. Sex ratios do not differ from parity, females are larger than males, and positive size-assortative mating occurs. Males fight (2–4% of beetles) over access to females, and disruption of mating usually follows these contests. In the laboratory, we compared mating and fighting frequencies for males found in mating pairs (field-paired) and single males placed into an arena with a field-paired female. Mating pairs were switched in half of arenas (new male-female pairs) and maintained in the other half. For 2 days, each male was free to move about and fight; thereafter males were tethered to prevent contests. Mating frequencies were significantly greater for field-paired than single males in both situations. Male size was not related to mating frequency; however, large females received more matings than small ones. These data suggest that males fight for high quality females, but otherwise search for as many matings as possible.     

Strategic responses of male samango monkeys (Cercopithecus mitis) to a decline in the number of receptive females

Observations on a habituated troop of samango monkeys (Cercopithecus mitis)revealed that lone males did not achieve significant mating opportunities during a breeding season in which few females were sexually receptive. This stood in contrast to the previous year and was associated with the maintenance of shorter resident male-female distances, confirming suggestions that the reproductive benefits of residency are associated primarily with low numbers of simultaneously receptive females. At the same time, lone males made no attempt to challenge the resident male physically in order to gain access to females. Given the presence of a stable bachelor group and the absence of other, transient, males, these data are used to argue for male mating strategies that are sensitive to regional and temporal variability in the availability of receptive females.     

Mating patterns in late-maturing female Mediterranean tarantulas may reflect the costs and benefits of sexual cannibalism

During courtship and mating, males of some invertebrate predators risk being killed and consumed by females, who in turn can obtain a foraging benefit from feeding on males. In these invertebrates, the sex ratio at the end of the mating season is usually female biased, probably due to sexual cannibalism and other sources of male mortality. Thus, at the end of the mating season males can be a limited resource to females as both mates and prey. Because of the high risk incurred when approaching females, males should show mate choice. To date there are little data on the costs and benefits of sexual cannibalism in natural populations. For one month we followed the mating patterns of 60 late-maturing Mediterranean tarantula, Lycosa tarentula L., females in a desert grassland population. The later a female matured, the shorter was her cohabitation time with males and the lower her probability of cohabiting with a male at all, suggesting that late-maturing females may be limited in their access to males as mates. At the end of the mating season, nonsexually cannibalistic late-maturing females also had poorer body conditions than did both sexually cannibalistic late-maturing females and early-maturing females, suggesting that late-maturing females may be also limited in their access to males as food. Females had higher mating success if they were smaller or in better condition (better fed). This pattern may reflect either male choice, or the possibility that small, well-fed females have higher mating success because they are less aggressive towards males. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Inter-male associations in a wild Japanese macaque troop on Yakushima Island,Japan

Adult male association and its annual change were studied in a wild population of Japanese macaques (Macaca fuscata yakui) on Yakushima Island, Japan. Unlike many other Japanese macaque troops, adult troop males frequently maintained proximity and exchanged grooming with one another in both the mating and non-mating seasons, and the dominance relationship rarely appeared in such inter-male associations. The few cases of agonistic interactions occurred mostly when estrous females or food resources were immediately concerned. Although troop males were very intolerant to newly appeared solitary males (new males) during the mating season, close associations were formed between troop males and new males as soon as the mating season terminated. The consort of new males and lower-ranking troop males with estrous females was frequently disturbed, but these males could copulate no less frequently than higher-ranking males. A comparison among macaque species suggests the existence of two forms of inter-male association: (1) the frequent association based on the symmetrical exchange of social behaviors; and (2) the infrequent and asymmetrical association related to the dominance relationship. The form of inter-male association seems to be influenced by whether or not males can keep close associations with females throughout the year.     

Male leadership change in a free-ranging troop of Indian rhesus monkeys (Macaca mulatta)

The male leadership of a troop of rhesus living at the foot of the Kumaon foothills of India was studied from January to December of 1965. The troop, inhabiting a region of fields and forests, varied in size from a maximum of 20 after the birth season to a minimum of 14 in December during the breeding season. The troop initially contained two adult males with the occasional presence of a third, more peripheral male. This third male disappeared in March and was perhaps identical with the male who began to appear in August and succeeded in displacing the dominant male from the troop. The second initial male succeeded to the dominant position in September. During the breeding season various extra-troop males followed and occasionally penetrated the troop. The second male had difficulty in maintaining his position against one of these, who had perhaps been the peripheral male at the beginning of 1965.     

Mate Discrimination in Invasive Whitefly Species

Mate discrimination could be critical for invasive species that need to locate rare suitable mates and avoid costs associated with misdirected courtships to establish in new environments. Here, we tested whether individuals of two invasive whitefly species in the Bemisia tabaci species complex, commonly known as the B and Q biotypes, could discriminate between potential mates based on their species and sex. Behavioral observations showed that B females were more discriminating than Q females. Males of both species were able to discriminate between mates based on their species and sex, but in general B males discriminated more effectively than Q males. By incorporating these behavioral data into a conceptual model, we show that variation in mating behavior between females of different species was a more significant factor affecting mating than variation between males. These results indicate that mate discrimination could affect interactions between whitefly species and influence a species’ ability to colonize novel environments.     

Jamaican Field Cricket Mate Attraction Signals Provide Age Cues

Older males often have a mating advantage, either resulting from the fact that they live longer or resulting from the fact that they both live longer and signal this to females. Male field crickets signal acoustically to attract potential mates. Some field cricket mating signals provide cues about male age while others do not. We explored whether male Jamaican field crickets, Gryllus assimilis, mating signals change with age. Our results show that older males produce chirps with longer pulses, more pulses, at higher pulse and chirp rates, and their chirps are both longer and louder than those produced by younger males. Our findings suggest that Jamaican field cricket mating signals provide cues about male age, explaining between 10% and 54% of the variation in signaling traits. Females might be able to use these mating signal differences to distinguish between older and younger mates.     

Female Defensibility in a Small Troops of Japanese Macaques vis-à-vis Nontroop Males and Copulation on the Periphery of the Troop

I provide data compiled over 4 yr on the mating behavior in small troops of wild Japanese macaques on Yakushima Island. The key parameters are the number of sexually receptive females, the number of nontroop males (NTMs), and copulation on the periphery of the troop. I analyzed the following aspects: 1) changes in the proportion of copulation with high-ranking males (HRMs) and NTMs, 2) variations in factors such as fluctuation in the number of sexually receptive females and troop males and their effects on the number of visiting NTMs, 3) the effect of attempted interruption of mounting series by other males, and 4) some aspects of copulation on the periphery of the troop. Throughout the study, 56% of the total number of females mated most frequently with the α-male in a single mating season. However, the relative mating success of HRMs varied over the years and between individuals. The number of visiting NTMs varied depending on the number of receptive females and troop males. Females tended to mate with the NTMs when they appeared around their troops. The direct effect of interruption of the mounting series by other males is equivocal. The females mated with the low-ranking males (LRMs) and NTMs on the periphery of the troop, which increased the possibility of mounting series ending with ejaculation. Females actively sought opportunities for copulation on the periphery of the troop by moving there or initiating close proximity with LRMs and NTMs there. On Yakushima Island, the mating success of HRMs was not always as high as that predicted by the priority of access model. The injury status of the HRM, the number of visiting NTMs, and female choice are all considered to influence a male’s mating success.     

Environmental Effects on Male Reproductive Success and Parental Care in the Florida Flagfish Jordanella floridae

Models of optimal parental care predict that parental investment should depend on offspring value or the effect parental care has on offspring benefits. Few studies have examined the effect of external factors that influence offspring survival and the cost of care. In this study on the Florida flagfish (Jordanella floridae), a species with male parental care, we examined whether environmentally induced changes in care result from changes in egg requirements or in parental costs. We manipulated salinity and temperature, as these factors are known to affect the metabolic rate in both eggs and parents. We predicted that if the change in care behavior is determined by costs to the male then it should be paralleled by changes in non‐egg‐directed behavior. Conversely, if egg‐directed behavior changes independently of other behavior it would suggest that behavior is determined primarily by egg requirements. In addition we examined patterns of mating success under the assumption that if male care is affected by environmental factors then female preferences may change accordingly. Males decreased egg‐directed behavior (fanning and cleaning of eggs) at high salinity. Non‐egg‐directed behavior was unaffected by salinity. Temperature had no effects on behavior. Thus, we conclude that changes in egg demands are primarily responsible for the observed results. Successful males were bigger and more aggressive. This suggests that male dominance was an important determinant of male mating success. Unsuccessful males showed significantly more variation in number of red stripes with respect to salinity than successful males. Unsuccessful males may be less able to regulate color expression under varying environmental conditions, in which case color may be an indicator of male quality. We replicated the experiment early and late in the season. Males did not change their effort in care over the season. However, care (fanning) in the absence of eggs increased towards the end of the season. Since pre‐mating fanning was positively correlated to a male’s eventual mating success we conclude that males increased their effort to attract mates late in the season.     

Measuring male-female relationships during the mating season in wild Japanese macaques (Macaca fuscata yakui)

Heterosexual relationships during one mating season were examined in a wild troop of Japanese macaques (Macaca fuscata yakui) on Yakushima Island, Japan. Validation tests of putative mate choice behaviors demonstrated that female initiation and maintenance of proximity, female lookback at the male, and sexual presents to the male, were associated with increased mating. Male grooming the female was also associated with increased mating. Ten dyadic social behaviors were subject to principal components analysis to empirically define behavioral dimensions of male-female relationships. The analysis yielded four relationship dimensions: ‘Mutual Choice and Male Coercion,’ ‘Female Choice’ (two types), and ‘Mutual Choice’ Dyads tended to be characterized by more than one dimension. The results suggested that females sought matings with multiple males of various dominance ranks. Female relationships with high ranking males contained elements of male coercion and mate guarding, however, because these males attempted to inhibit females from mating with lower ranking males. The correlation between each relationship dimension and mating success depended, in part, on the dominance rank of males. Relationships involving high ranking males, which were most likely to contain elements of male coercion and mate guarding, were associated with mating success. Relationships involving low ranking males, which usually lacked such coercive elements. were less strongly correlated with mating success. These results, obtained from a wild troop, are compared to those previously obtained in captive and provisioned groups of Japanese macaques.     

Female mate preferences on high‐dimensional shape variation for male species recognition traits

Females in many animal species must discriminate between conspecific and heterospecific males when choosing mates. Such mating preferences that discriminate against heterospecifics may inadvertently also affect the mating success of conspecific males, particularly those with more extreme phenotypes. From this expectation, we hypothesized that female mate choice should cause Enallagma females (Odonata: Coenagrionidae) to discriminate against conspecific males with more extreme phenotypes of the claspers males use to grasp females while mating – the main feature of species mate recognition in these species. To test this, we compared cerci sizes and shapes between males that were captured while mating with females to males that were captured at the same time but not mating in three Enallagma species. In contrast to our hypothesis, we found only one of forty comparisons of shape variation that was consistent with females discriminating against males with more extreme cerci shapes. Instead, differences in cerci shape between mating and single males suggested that females displayed directional preferences on 1–4 aspects of cerci shape in two of the species in our samples. These results suggest that whereas some directional biases in mating based on cerci shape occur, the intraspecific phenotypic variation in male cerci size and shape is likely not large enough for females to express any significant incidental discrimination among conspecifics with more extreme shapes.     

LIFETIME REPRODUCTIVE SUCCESS AND THE OPPORTUNITY FOR SELECTION IN A NONTERRITORIAL DAMSELFLY (ODONATA: COENAGRIONIDAE)

Major components of male and female lifetime reproductive success (LRS) were quantified for a damselfly that exhibits “scramble competition” for mates. The opportunity for selection on male reproduction was potentially 2.9 times that for females. Differential fertility/clutch and survivorship each accounted for about half of the total variation in female reproductive success. Variation in fertilization efficiency accounted for 7% of the total opportunity for selection on males. Although differences in survivorship and mating efficiency each contributed to about a third of the total opportunity for selection on male reproduction, both components appeared to be influenced by random factors. Survivorship was age-independent, and the mating distributions among males with equal mating opportunities were indistinguishable from those expected if matings were random with respect to male phenotype. Because the proportion of the standarized variance (I) in LRS that was attributed to sexual selection depended on the way the selective episodes were defined, the sample of individuals included in the partitioning analysis, and the degree of sexual selection on mated males that could be detected, my results caution against drawing conclusions about the dynamics of sexual selection on populations based on a superficial comparison of I values.