Seasonal variation in sexual behavior of all-male rhesus troops

Free roaming groups of Rhesus monkeys show a clear annual cycle in the incidence of sexual behavior. One hypothesis explaining the control of this cycle is that seasonal variables act directly on females, altering their endocrine status. Aroused females then communicate their sexual receptivity to male group members. The sexual behavior of 35 male Rhesus was observed during the non-mating and the mating season. All animals were maintained in large outdoor enclosures. One group of males (N = 7) were housed with females and juveniles as part of a breeding group. A second group of males (N = 8) had visual contact with the members of the breeding group, and a third group of males (N = 20) had no contact with either of these groups. During the non-mating season no sexual behavior was observed. At the onset of the mating season, the males with females displayed evidence of hormonal arousal and became sexually active. The males with visual contact with the breeding group also evidenced hormonal arousal and began engaging in male-to-male sexual activity. The males in the third group showed no sign of sexual arousal. These findings support the hypothesis that seasonal influences act only on females; and demonstrate that females can communicate their endocrine status to males, even without direct physical contact.     

Male ornamentation and its condition-dependence in a paternal mouthbrooding cardinalfish with extraordinary sex roles

Cardinalfishes, in which males alone provide mouthbrooding, are likely candidates for sex-role reversal because of a higher potential reproductive rate for females than for males. In the gregarious cardinalfish, Apogon notatus, females establish breeding territories to form pairs prior to the breeding season. Within breeding pairs, females are more active in courtship and in attacks against conspecific intruders. Sex roles thus seem to be behaviorally reversed. The operational sex ratio is, however, male-biased because females suffer higher mortality than males and consequently males predominate in number in the adult population, leading to the prediction that males would be sexually selected. In the present study, morphological measurements showed that males had a protrudent lower lip that was expressed markedly during the breeding season. Field observation revealed that males with a longer and wider lip were preferentially accepted as a mating partner by territorial females. The male lip size positively correlated with their somatic condition, suggesting that the ornamental lip has evolved through indicator mechanisms of sexual selection. By contrast, females had longer fins than males, but these sexual dimorphisms were less pronounced and most of them were seasonally constant. These results support the prediction that sexual selection acts on males in this fish. Electronic Publication     

Pituitary luteinizing hormone responses to single doses of exogenous GnRH in female social Cape ground squirrels exhibiting low reproductive skew

The Cape ground squirrel Xerus inauris is unusual among social mammals as it exhibits a low reproductive skew, being a facultative plural breeder with not all females breeding within a group. We investigated pituitary function to assess whether there was reproductive inhibition at the level of the pituitary and potentially the hypothalamus in breeding and non-breeding female Cape ground squirrels. We did so during the summer and winter periods by measuring luteinizing hormone (LH) responses to single doses of 2 g exogenous gonadotropin-releasing hormone (GnRH) and physiological saline administered to 42 females from 11 colonies. Basal LH concentrations of females increased in response to the GnRH challenge. Basal plasma LH concentrations were greater during winter, when most oestrus events are observed. However, we found no differences in plasma LH concentrations between breeding and non-breeding females. We showed that the anterior pituitary of non-breeding female ground squirrels is no less sensitive to exogenously administered GnRH than that of breeding females. We therefore concluded that the pituitary is no more active in breeding than non-breeding females. The lack of differentiation in response to GnRH suggests that either non-breeding females have ovaries that are less sensitive to LH or that they refrain from sexual activity with males through an alternative mechanism of self-restraint.     

The costs of reproduction to males and females of a paternal mouthbrooding cardinalfish Apogon notatus

In the cardinalfish Apogon notatus , starving males mouthbrood the eggs, and females are more active than males in courtship and in attacks against conspecific intruders upon their breeding territory, but sexual ornaments are developed in males. Condition factor, hepatosomatic index and fat body-somatic index declined in both sexes during the breeding season. The deterioration of somatic condition was more severe in females, suggesting that the overall energetic costs were larger for females which produced more than twice as many clutches as males brooded in a season. Selective mortality of females could be due primarily to the depletion of their energy reserves. The increased mortality in females is a possible mechanism for the male-biased operational sex ratio which may provide the potential for sexual selection on males.     

Co-existence of subadult males and females as alternative tactics of breeding post acquisition in a monogamous and protandrous anemonefish

Summary The monogamous and protandrous anemonefish,Amphiprion clarkii, utilizes only large host sea anemones as breeding sites. Under conditions of breeding site shortage, an important strategy for unmated fish may be to prepare themselves to enter quickly a breeding site from which a breeding male or female has recently disappeared. There are two types of subadults. Some juveniles become subadult males, which can change either to male or female afterwards, but others become subadult females, which can change only to female. Subadult females seem to acquire female posts more easily than subadult males. We develop an ESS model which evaluates the future reproductive success of subadult females and subadult males and test whether coexistence of subadult males and females can be interpreted as adaptive alternative tactics, using field data from two populations. The model predicts that if mortality does not differ between adult males and females the frequency for juveniles to become subadult females should be equal to the proportion of breeding post acquisition by subadult females among that by all subadults. The model also predicts that if mortality does not differ between subadult males and females, nor in adults, the frequency of subadult females among all subadults should be equal to the proportion of post acquisition. The model, with data from two study sites, suggests that alternative life-history pathways found inA. clarkii have evolved through adaptive tactics of breeding post acquisition.     

Sexual selection is stabilizing selection in pupfish [Cyprinodon pecosensis)

One of the predictions of the 'good genes' model of sexual selection is that reproductively successful males with well-developed indicator traits should show smaller variances for non-indicator traits, that are not directly associated with mating success, when compared to non-breeding males and females. Thus sexual selection should reinforce stabilizing natural selection in reducing the variance in quantitative traits. This prediction is tested by analysing variation in eight morphological traits of breeding males, non-breeding males, and females of pupfish (Cyprinodon pecosensis). Breeding males tended to be less variable than non-breeding males for all principal component factors, and for all morphological traits except for depth, although these differences were statistically significant only for PC2, and PC5 and for pelvic fin length, number of pelvic fin rays and number of preopercular and preorbital pores. Similarly, breeding males tended to be less variable than females for all principal component factors and for all morphological traits except for number of preopercular pores. These differences were statistically significant for PC2, and for depth, pelvic fin length, number of preorbital pores and pectoral fin rays. The overall pattern of reduced variability in independent traits of breeding males revealed by principal component analysis is very consistent and highly significant (P<10⁵). These results support the prediction of the 'good genes' model and show that reproductively active males are subject to more severe stabilizing selection for several quantitative traits than non-breeding males and females. Thus sexual selection, through male-male competition, female choice, or an interaction of both selective processes, results in stabilizing selection on quantitative morphological traits.     

Effects of reproductive state on vocalizations in squirrel monkeys (Saimiri sciureus)

Vocalizations and behavior of a group of 6 squirrel monkeys, 2 males and 4 females, were recorded during the nonbreeding and breeding seasons. Behavioral and physical criteria were used to determine the presence of estrus. During the breeding season the types of vocalizations uttered by estrous females changed, and the adult male increased his rate of vocalizing. Err vocalizations by estrous females were associated with increased following and initiation of affiliative behavior with the adult male, and may have functioned to facilitate these interactions. Errs appeared to be related to changes in female reproductive state rather than to the behavior of others. The adult male increased vocalizations associated with sexual and aggressive behavior (squeals and cackles), primarily in response to the estrous females' persistent initiation of interactions with him. We concluded that certain vocalizations in Saimiri reflected changes in the reproductive state of males and females, and functioned to mediate changes in social bonding during the breeding season.     

Environmental tracking by females

Human females are generally reserved in their sexuality, in keeping with their heavy investment in reproduction. Males tend to be less reserved. Relative to males, however, females demonstrate more variability in sexuality and are more likely to inhibit or express high levels of sexuality. The heightened variability may in part originate with genetic mechanisms that predispose females toward greater variability (the Lyon hypothesis). Menarche, menstrual cycles, menopause, food reactions, responses to living conditions, reactions to cultural factors, and responses to sexual stimuli and potential mates are unique to or are more variable among females than males. There is a correlation between the variation expressed and female reproductive potential—females tend to shift dramatically from sexual inhibition to sexual expression. Females apparently track the quality of the environment and link their sexuality to reproductive opportunities. Successful male reproduction depends less on quality environments and more on the availability of females. In short, females track the environment; males track the females.     

嘉陵江下游蛇鮈的两性异形与雌性个体生殖力

为了解蛇鮈雌雄间是否存在显著的外部形态差异及雌性个体生殖力情况, 在繁殖期对嘉陵江下游(合川江段)共76尾蛇鮈样本的两性异形、性比及雌性个体生殖力进行分析.结果表明: 嘉陵江下游蛇鮈繁殖群体的性比接近1∶1,且蛇鮈两性的体型大小相同,但局部特征(如头部和躯干部等)呈现出显著的两性异形,如成体雄性蛇鮈的头部、胸鳍和腹鳍均较雌性蛇鮈大,而躯干部的体宽、体高和躯干长则是雌性蛇鮈大于雄性蛇鮈,这可能是性选择长期作用的结果.主成分分析显示,前3个主成分的累积贡献率达75.2%,但雌雄个体间形态特征相互重叠,无法将两者截然分开;利用判别函数对蛇鮈性别进行回判,综合判别准确率为92.1%.蛇鮈雌性个体绝对生殖力在979～19979粒;且与体长和去内脏体质量均呈显著正相关.同历史资料相比,本研究中嘉陵江蛇鮈的生殖力增大显著,这可能是蛇鮈对种群资源量下降和水环境变化主动适应的结果.     

Behavioral and physiological female responses to male sex ratio bias in a pond-breeding amphibian

Introduction

The phenomenon of sexual conflict has been well documented, and in populations with biased operational sex ratios the consequences for the rarer sex can be severe. Females are typically a limited resource and males often evolve aggressive mating behaviors, which can improve individual fitness for the male while negatively impacting female condition and fitness. In response, females can adjust their behavior to minimize exposure to aggressive mating tactics or minimize the costs of mating harassment. While male-male competition is common in amphibian mating systems, little is known about the consequences or responses of females. The red-spotted newt (Notophthalmus viridescens) is a common pond-breeding amphibian with a complex, well-studied mating system where males aggressively court females. Breeding populations across much of its range have male-biased sex ratios and we predicted that female newts would have behavioral mechanisms to mitigate mating pressure from males. We conducted four experiments examining the costs and behavioral responses of female N. viridescens exposed to a male-biased environment.

Results

In field enclosures, we found that female newts exposed to a male-biased environment during the five-month breeding season ended with lower body condition compared to those in a female-biased environment. Shorter-term exposure to a male-biased environment for five weeks caused a decrease in circulating total leukocyte and lymphocyte abundance in blood, which suggests females experienced physiological stress. In behavioral experiments, we found that females were more agitated in the presence of male chemical cues and females in a male-biased environment spent more time in refuge than those in a female-biased environment.

Conclusions

Our results indicate that male-biased conditions can incur costs to females of decreased condition and potentially increased risk of infection. However, we found that females can also alter their behavior and microhabitat use under a male-biased sex ratio. Consistent with surveys showing reduced detection probabilities for females, our research suggests that females avoid male encounters using edge and substrate habitat. Our work illustrates the integrated suite of impacts that sexual conflict can have on the structure and ecology of a population.     

Seasonal changes in reproductive behavior in two ovariectomized female rhesus monkeys treated year-round with estradiol

Two ovariectomized female rhesus monkeys treated year-round with estradiol-filled capsules were used in hour-long behavioral tests with male rhesus monkeys both in and out of the normal breeding season. The study was designed primarily to test male hormonal responses to copulatory behavior and it was expected that behavior of the females would be essentially the same under both seasonal conditions. Several behaviors of the female, however, were found to fluctuate on a seasonal basis, namely (1) proximity to the male, (2) grooming of the male, (3) sexual presentations, and (4) threatening away (a form of sexual invitation). All of these behaviors, except proximity, were found to be positively correlated with the male partner's testosterone levels before and after the behavior test in the only test condition in which most males ejaculated. The preliminary suggestion is made that these females responded to some cue, either from the environment or from the males, that caused a change in their behavior between breeding and nonbreeding seasons despite the constant hormonal environment provided by the estradiol capsules. Since the same behaviors which were sensitive to seasonal effects were positively correlated with male testosterone levels, it is possible that the male's hormonal status affects affects female behavior.     

Fitness consequences of divorce in the azure-winged magpie depends on the breeding experience of a new mate

Sexual conflict in producing and raising offspring is a critical issue in evolutionary ecology research.Individual experience affects their breeding performance,as measured by such traits of provisioning of offspring and engagement in extra-pair copulations,and may cause an imbalance in sexual conflict.Thus,divorce is hypothesized to occur within aged social pairs,irrespective of current reproductive success.This concept was explored in the azure-winged magpie Cyanopica cyanus by investigating the divorce of a social pair and its relationship to their changes in breeding performance with prior experience.Females engaging in extra-pair copulation may intensify sexual conflicts and may be the main reason for divorce.Once divorced,females repairing with an inexperienced male realized higher reproductive success than that repairing with an experienced male;males repairing with an experienced female realized higher reproductive success than that repairing with an inexperienced female.This finding indicates that the fitness consequence of divorce depends on the breeding experience of new mates.Divorced females can obtain more extra-pair copulations,whereas divorced males cannot,when they repair with inexperienced breeders.Divorced females provisioned a brood at lower rates than inexperienced females whereas divorced males had no such difference.It appears that divorced females can obtain an advantage in sexual conflicts with inexperienced mates in future reproduction.Consequently,females are probably more active than males in divorcing their aged mates so as to select an inexperienced male as a new mate.Azure-winged magpies thus provide novel insights into the implicaticns of sexual conflict in birds.     

Coping with predators and food limitation: testing life history theory for sex–specific larval development

For animals with complex life cycles, recent models of sexual size-dimorphism at maturity assume three key variables to optimise larval life history: activity in the larval stage, development time, and size at maturation. However, model predictions remain largely untested. In the territorial dragonfly Libellula depressa (Odonata) exhibiting a flexible development time we tested for male-biased sexual size-dimorphism and sex differences in larval activity, development time, and growth rate. Based on models we predicted that males achieved their larger size compared to females by a longer development rather than being more active. Results revealed that males took longer to develop and achieved a larger size than females but were not more active. Compared to males, females exhibited a higher growth rate which was not achieved by an activity-mediated increased food intake. We conclude that sexual size-dimorphism in species with a flexible development time is mediated by differences in developmental length but not activity. Furthermore, sexes differ in their plastic responses to food availability and predator presence making it necessary to consider sex-specific differences in testing further life history responses.     

黄腹山鹪莺稳定的配偶关系限制雄性欺骗者

多数鸟类通过性特征限制在同性竞争和配偶选择中的“欺骗者”存在,与此相反,雀形目扇尾莺科部分物种表现出繁殖季节性特征消退的身体特征变化模式.在广州市南沙区通过“目字笼”对黄腹山鹪莺配偶关系稳定性的限制机制进行研究,发现虽然雌性个体到访原配个体和对照个体的次数几乎相同,但是雌性个体对原配雄性的单次选择时间明显长于对照雄性个体,总计选择时间也明显长于对照雄性个体.选择实验过程中,原配雄性的跳动次数明显高于对照个体雄性,以竖尾扑哧和鸣声恐吓等为代表的威慑行为次数也明显高于对照雄性个体.结果说明,雌性更青睐于原配个体,配对时间越长,忠诚度越高,而且原配雄性比入侵雄性个体表现出更高的活跃度和威慑行为.繁殖季节性特征消退的物种可以通过保持稳定的配偶关系以限制“欺骗者”存在.可以推测繁殖的巨大投入和雌性之间的同性竞争可能是产生这种配偶稳定性的主要原因.     

Sexual behavior of the female porcupine Hystrix africaeaustralis

Porcupines are sexually active throughout the estrous cycle, and sexual behavior is not affected by the reproductive status and hormonal milieu of females. Increased female-male interactions during estrus are the only indications of behavioral changes during estrus. The lack of aggression shown by females to known males as opposed to aggression shown to strange males, the greater interest shown by males toward certain females, and the superior breeding success of these females suggest a pair-bonding mating system. Limited changes in female receptivity throughout the cycle might be of importance in maintaining the pair-bond.     

Effects of breeding site density on competition and sexual selection in the European lobster

The availability of breeding sites has been predicted to affectthe intensity of sexual selection, including mate competition,mate choice and ultimately, variation in mating success. Wetested the hypothesis that reduced density of shelters wouldcause an increase in the intensity of sexual selection in Europeanlobsters, Homarus gammarus. However, we found little supportfor our predictions. For example, within-sex competition bymales and by females was not more intense when shelters werescarce. Indeed, females attempted to evict one another fromshelters significantly more often when shelters were common.When shelters were abundant, shelter-holding males had greatermating success than males without shelters, yet females didnot show more interest towards these males during courtshipencounters. Mate attraction was more strongly related to largemale body size when shelters were scarce. Overall, the resultssuggest that reduced shelter density does not lead to more overtwithin-sex aggression in this species. Instead, we suggest thatimpacts of breeding resource availability on sexual selectionmay depend on the range over which resources are measured, withextreme scarcity of shelters rendering overt competition uneconomical.Furthermore, females may become more selective of male traitssuch as large size, which enhance male control of breeding sitesand hence protection of females.     

Behavioral responses to physical vs. social novelty in male and female laboratory rats

Most behavioral tests used with laboratory rodents involve measuring behavioral responses to physical novelty. However, laboratory rodents are often derived from highly social species for which novel social stimuli may induce different levels of fear or curiosity compared to novel physical objects. We hypothesized that behavioral responses will differ in response to novel physical vs. social cues, and that females may show more exploration of social novelty, based on prior studies indicating that females more actively seek social support during duress compared to males. We compared young (55-day-old) Sprague-Dawley rats’ responses to an arena filled with novel objects (“physical”) or a novel same-sex caged conspecific (“social”). Rats were more active and spent twice as much time in contact with the novel social stimulus compared to novel physical stimuli. Although females were more active than males, females were not particularly more exploratory in the social arena compared to males. The results indicate that a novel social partner (even a caged one with limited ability to interact) elicits more exploration than novel objects for both male and female rats.     

Sexual selection, stabilizing selection and fluctuating asymmetry in two populations of pupfish (Cyprinodon pecosensis)

Fluctuating asymmetry of morphological traits is thought to reflect the capacity of a genotype to produce an integrated, functional phenotype. I tested three predictions. (1) In a polygynous breeding system, under intense sexual selection on males, breeding males should show greater symmetry in bilaterally symmetrical traits than non-breeding males or females. (2) If these traits are under stabilizing selection, highly symmetrical individuals also should be modal phenotypes, thus near the mean value for that trait, whereas individuals with increased asymmetry should represent marginal phenotypes, near the extremes of the distribution for that trait. (3) Differences in the intensity of sexual selection should be reflected in differences in the degree of fluctuating asymmetry between sexes among populations. I examined the relationship between male breeding status and the degree of fluctuating asymmetry of four bilaterally symmetrical- traits, preorbital and preopercular pores and pectoral and pelvic fin rays, in two populations of Pecos pupfish which differed in the intensity of sexual selection. These traits do not function in male-male competition or female choice, thus are not directly affected by sexual selection. In Mirror Lake breeding males, as a group, were most symmetrical for all four traits, while non-breeding males and females showed higher levels of fluctuating asymmetry. Similarly, symmetrical individuals also represented modal phenotypes for four traits (breeding males), and for three traits (non-breeding males and females). These patterns were not seen in the Lake Francis population, where breeding males were as asymmetrical as non-breeding males and females, and the degree of fluctuating symmetry did not differ between modal and marginal phenotypes for any of the four traits. When ecological conditions favour intense sexual selection, either through female choice, male-male competition, or both, breeding males represent the most fit phenotypes. Thus sexual selection reinforces the effects of stabilizing selection on characters that do not function as secondary sexual traits. However, when sexual selection is relaxed, differences between sexes disappear.     

Experimental tests of endocrine function in breeding and nonbreeding raptors

Many long-lived avian species defer reproduction for several years, often displaying a "floating" behavior characterized by the lack of mates and exclusive territories. Understanding the proximate mechanisms regulating floating behavior is a relevant topic of research for physiologists, behavioral ecologists, and population biologists because a prolonged period of nonbreeding can negatively affect lifetime fitness and change population dynamics. Here we tested two hypotheses linking endocrine function to floating status: (a) floaters undergo a period of sexual immaturity characterized by lower gonadal function (hypothesis of sexual immaturity), and (b) floating status is socially imposed by dominant conspecifics and revealed by the adrenocortical response to stress (hypothesis of social subordination). The two hypotheses were tested in a population of free-living black kites Milvus migrans in Do?ana National Park (southwest Spain), where breeders coexist with young floaters that defer reproduction for 3-7 yr. Hypophysial-gonadal function, estimated as androgen production in response to experimental challenge with gonadotropin-releasing hormone (c-GnRH-I), was similar in magnitude and timing between floating and breeding males. The same treatment was, however, unable to elicit any response in terms of increasing estradiol or total androgen levels in females regardless of their breeding status. Following experimental capture and restraint, the adrenocortical response to stress (estimated as circulating corticosterone levels) was higher in floating than in breeding males, while females showed the opposite pattern (i.e., lower response to stress in young floaters compared with breeders). Contrary to the hypothesis of sexual immaturity, our results suggest that floating males are physiologically capable of reproducing. The reported differences in adrenocortical function support the idea that floaters are socially subordinate to breeders, and corticosterone responses reflect the sex-specific roles during competition in socially monogamous species.     

The Role of Sex-specific Plasticity in Shaping Sexual Dimorphism in a Long-lived Vertebrate,the Snapping Turtle <Emphasis Type="Italic">Chelydra serpentina</Emphasis>

Sex-specific plasticity, the differential response that the genome of males and females may have to different environments, is a mechanism that can affect the degree of sexual dimorphism. Two adaptive hypotheses have been proposed to explain how sex-specific plasticity affects the evolution of sexual size dimorphism. The adaptive canalization hypothesis states that the larger sex exhibits lesser plasticity compared to the smaller sex due to strong directional selection for a large body size, which penalizes individuals attaining sub-optimal body sizes. The condition-dependence hypothesis states that the larger sex exhibits greater plasticity than the smaller sex due to strong directional selection for a large body size favoring a greater sensitivity as an opportunistic mechanism for growth enhancement under favorable conditions. While the relationship between sex-specific plasticity and sexual dimorphism has been studied mainly in invertebrates, its role in long-lived vertebrates has received little attention. In this study we tested the predictions derived from these two hypotheses by comparing the plastic responses of body size and shape of males and females of the snapping turtle (Chelydra serpentina) raised under common garden conditions. Body size was plastic, sexually dimorphic, and the plasticity was also sex-specific, with males exhibiting greater body size plasticity relative to females. Because snapping turtle males are larger than females, sexual size dimorphism in this species appears to be driven by an increased plasticity of the larger sex over the smaller sex as predicted by the condition-dependent hypothesis. However, male body size was enhanced under relatively limited resources, in contrast to expectations from this model. Body shape was also plastic and sexually dimorphic, however no sex by environment interaction was found in this case. Instead, plasticity of sexual shape dimorphism seems to evolve in parallel for males and females as both sexes responded similarly to different environments.