Sex differences in cognition and their relationship to male mate choice

Male cognition has gained recognition as an important potential player in sexual selection. A number of studies have found positive correlations between male sexual signals and cognitive performance an d/or female pref ere nces for males with better cog nitive performance, although other studies have not fou nd these relati on ships. Sex roles can differ dramatically, and sex differen ces in selection on cog nition likely follow from the different tasks associated with these sex roles. Here, using threespine stickleback Gasterosteus aculeatus, a species with clearly diverge nt sex roles and mutual mate choice, we focus on the cognitive trait inhibitory control because males must differentially respond to reproductive females versus other sticklebacks while defending territories and refrain from eating eggs and fry while performing paternal care. We presented fish with a detour task four times over a period of 7 days, allowing us to assess initial inhibitory control and improvement over time. We ask 1) whether there are sex differences in inhibitory control and 2) whether male mate choice is associated with female inhibitory control. Although males outperformed females on three different measures of detour task performance across four trials, these differences were largely explained by males being less neophobic than females. Females took more trials to successfully solve the detour task, even after accounting for sex differences in neophobia. Female cognitive abilities, however, were unrelated to the vigor with which males courted them. The equivocal results regarding sex differences in cognitive ability suggest further study given the very different selection pressures each sex experiences.     

Sex roles and mutual mate choice matter during mate sampling

The roles of females and males in mating competition and mate choice have lately proven more variable, between and within species, than previously thought. In nature, mating competition occurs during mate search and is expected to be regulated by the numbers of potential mates and same-sex competitors. Here, we present the first study to test how a temporal change in sex roles affects mating competition and mate choice during mate sampling. Our model system (the marine fish Gobiusculus flavescens) is uniquely suitable because of its change in sex roles, from conventional to reversed, over the breeding season. As predicted from sex role theory, courtship was typically initiated by males and terminated by females early in the breeding season. The opposite pattern was observed late in the season, at which time several females often simultaneously courted the same male. Mate-searching females visited more males early than late in the breeding season. Our study shows that mutual mate choice and mating competition can have profound effects on female and male behavior. Future work needs to consider the dynamic nature of mating competition and mate choice if we aim to fully understand sexual selection in the wild.     

Population Genetics and Phylogeography of Bufo gargarizans in China

The Chinese toad Bufo gargarizans has an extensive range, covering nearly all of China. This study addresses the population genetic structure of this toad and the relation to geographic location. Partial sequences of the mtDNA control region were obtained from 14 populations, 29 haplotypes were defined, and 73 variable sites were found, including 66 parsimony informative sites. All population genetic analyses indicated no clear geographic pattern in the distribution of haplotypes. The genetic divergence between the populations was significant. Phylogeographic analyses suggested that past fragmentation and/or long-distance colonization seemed to have shaped the present-day distribution of the haplotypes of B. gargarizans.     

Interspecific mate choice by late-courting male western grebes

In mixed populations of western and Clark's grebes, advertisingcalls by males and females play a critical role in mate choiceand reproductive isolation. We conducted field playback experimentsthat tested whether courting western grebe males became lesschoosy in their responses to female Clark's grebe calls as themating season progressed and mating opportunities diminished.Late-courting western grebe males were much more likely to answerand approach advertising calls of Dark's grebe females thanwere males courting earlier in the season. This change in responsivenessoccurred as the operational sex ratio index of the populationapproached 3:1 male calls per female call. These and field censusdata support the hypothesis that late-season hybridization betweenthese two closely related species may be a result not of speciesmisidentification, but of active and adaptive mate choice byindividuals with limited alternatives.     

Reversible frequency-dependent switches in male mate choice

Current sexual-selection theories predict that mating should occur preferentially with the highest-quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency-dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency-dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness.     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

Female mate choice is not affected by mate condition in a fish with male care

Several studies have shown that mate choice based on condition leads to higher reproductive success of the choosing individual. Yet, a growing body of literature has failed to find support for mate choice based on mate condition, even when the choosing individual would clearly benefit from such a choice. This indicates that animals’ mate choice is often more complex than currently appreciated and that even well-founded expected preferences cannot be taken for granted. Using the broad-nosed pipefish, Syngnathus typhle, we manipulated male condition experimentally to explore whether it affects female mate choice. In this sex-role-reversed species, males care for the offspring in a specialised brood pouch. Males are the choosier sex, but given the opportunity, females are selective as well. During brooding, males can both provide embryos with nutrients and take up nutrients that originate from eggs deposited in the pouch, and embryo survival correlates positively with male condition. Together, this suggests that it would be beneficial for females to mate with males in high condition. However, we found no female preference for males in better condition. Thus, this study adds to the literature of mate choice that is unaffected by mate condition. Possible reasons for our result are discussed.     

The evolution and significance of male mate choice

The distinct reproductive roles of males and females, which for many years were characterised in terms of competitive males and choosy females, have remained a central focus of sexual selection since Darwin's time. Increasing evidence now shows that males can be choosy too, even in apparently unexpected situations, such as under polygyny or in the absence of male parental care. Here, we provide a synthesis of the theory on male mate choice and examine the factors that promote or constrain its evolution. We also discuss the evolutionary significance of male mate choice and the contrasts in male versus female mate choice. We conclude that mate choice by males is potentially widespread and has a distinct role in how mating systems evolve.     

Female choice and the benefits of mate guarding by male mallards

Pair formation and breeding in many species of waterfowl are separated both temporally and spatially. Most studies of female choice in this group have focused on male characteristics at the time of pairing, with less attention given to how mate choice affects breeding season outcomes. In this study I compared pairing success, male plasma testosterone level and mate-guarding ability of male mallards, Anas platyrhynchos, in two experiments. In the first experiment females and males were group housed with equal sex ratios, thus allowing all of these males to pair. At the same time, an equal number of males was housed in groups without access to females and remained unpaired. In this experiment testosterone levels of paired and unpaired males during autumn (baseline) and spring (breeding) did not differ, indicating that the process of pair formation and breeding does not cause elevated spring testosterone levels in males. However, testosterone did temporarily decrease in paired males during the winter (pair formation) season. In the second experiment groups were male biased, allowing only half of the males to pair. Here paired males had significantly higher testosterone levels than unpaired males during the breeding season, but not during the preceding autumn. Together the results of these experiments indicate that successful pair formation predicts but does not alter male testosterone level during the breeding season. I also found that females paired to males with high levels of testosterone were missing fewer feathers due to forced copulation attempts by nonmates, suggesting that females may choose males based on their mate-guarding abilities. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Costs influence male mate choice in a freshwater fish

It is well known that female mate choice decisions depend on the direct costs of choosing (either because of search costs or male-imposed costs). Far less is known about how direct fitness costs affect male mate choice. We conducted an experiment to investigate male mate choice in a fish, the Pacific blue-eye (Pseudomugil signifer). Preferred females were larger, probably because larger females are also more fecund. Males, however, were consistent in their choice of female only when the costs of associating with prospective mates were equal. By contrast, males were far less consistent in their choice when made to swim against a current to remain with their initially preferred mate. Our results suggest that males may also respond adaptively to changes in the costs of choosing.     

Female mate choice in a mating system dominated by male sexual coercion

In poeciliid fishes, males can gain copulation either by courtingfemales or through sexual coercion. In some species these twotactics coexist. However, in about half of the poeciliids,males do not display, females never cooperate during copulationand all matings are achieved by thrusting the intromittentorgan toward the genital pore of apparently unaware females.In one of these species, the eastern mosquitofish (Gambusiaholbrooki), the probability of insemination is influenced bythe time females are previously deprived of males, suggestingthat females exert some control over the occurrence of matingeven in a system apparently dominated by sexual coercion. Inthe present study we investigated the tendency of female mosquitofishto approach males in relation to their reproductive status and the time they were previously deprived of males. The tendencyto approach males increased in females that were previouslydeprived of males and in females that had recently given birth.When allowed to choose between males, male-deprived femalespreferred larger males and normally pigmented over melanisticmales. Females preferred groups of three males over a singlemale, whereas the preference for three males over a group ofone male and two females was only marginally significant. Collectively,these results suggest that, even when coercive mating is theonly tactic adopted by males, females may be able to influencethe outcome of these attempts, and thus exert some controlover the paternity of their offspring.     

Geographical variation in reproductive character displacement in mate choice by male sailfin mollies

Female Amazon mollies, Poecilia formosa, are a unisexual species that reproduce by gynogenesis. They must coexist and mate with males of other species (usually the mollies Poecilia latipinna or Poecilia mexicana) to induce embryogenesis, but inheritance is strictly maternal. We examined the mating preference of the male sailfin molly, P. latipinna, for female sailfin mollies versus Amazon mollies, P. formosa. We compared the mating preferences of sympatric and allopatric populations collected throughout the Gulf Coast of North America. Male P. latipinna from six populations sympatric with Amazon mollies showed a significantly greater strength of preference for conspecific sailfin females than males from five populations that were allopatric with Amazon mollies. These results provide strong evidence for reproductive character displacement of male mate choice in sympatry. Furthermore, the large geographical range of populations that we tested revealed variation among populations within sympatry and allopatry, indicating that it is important to evaluate a large number of populations when examining reproductive character displacement.     

Balancing sexual selection through opposing mate choice and male competition

Male–male competition and female mate choice act contemporaneously in the cockroach Nauphoeta cinerea and the social pheromone of males influences the outcome of both forms of sexual selection. We therefore examined the joint and separate effects of male–male competition and female mate choice to determine if the selective optima for the pheromone were the same or different. Dominant males in a newly established hierarchy mated more frequently, but not exclusively. Manipulations of the multi-component social pheromone produced by males of N. cinerea showed that both long- and close-range attraction of females by males were influenced by the quantity and composition of the pheromone. The most attractive composition, however, differed from that which was most likely to confer high status to males. Since the outcome of male–male competition can conflict with mating preferences exhibited by females, there is balancing sexual selection on the social pheromone of N. cinerea. Such balancing selection might act to maintain genetic variation in sexually selected traits. We suggest that the different forms of sexual selection conflict in N. cinerea because females prefer a blend different to that which is most effective in male–male competition in order to avoid mating with overly aggressive males.     

Correlated changes in male plumage coloration and female mate choice in cardueline finches

The coevolution of extravagant male traits and female mate preferences is a central tenet of sexual selection theory. In lineages in which males have developed more elaborate sexual characters, females favour the most extreme expression of the trait. In some taxa, however, ornamental displays have evolved from more to less exaggerated states. Under these circumstances, it is unclear whether females show preferences for an ancestral male condition or for the current, less elaborate display. Here, we tested female mate preferences relative to male ornamental coloration in two species of cardueline finch (the American goldfinch, Carduelis tristis, and pine siskin, Carduelis pinus) that have evolved less elaborate carotenoid-based colour displays from more elaborately coloured ancestral states. We presented females of each species with a choice of males having either large patches of red colour (the elaborate, ancestral condition) or with species-typical patches of yellow colour (the less elaborate, derived state). Female goldfinches and siskins showed consistent preferences for the natural colour displays of males, and not for the more elaborate, ancestral colour pattern. Previous research on another cardueline finch taxon (a subspecies of the house finch, Carpodacus mexicanus griscomi), however, showed that females prefer more elaborate, ancestral coloration to the current form of reduced colour expression. The lack of congruence between male trait expression and female trait preference in the lineage with the most recently derived reduction in trait expression suggests that there may be evolutionary lags in the correspondence between male traits and female preferences. A shift in the expression of male coloration appears to be the first step towards the evolution of reduced colour displays in these finches.     

中华大蟾蜍TAGLN2 cDNA的克隆与其组织分布

为研究蟾蜍(Bufo)基原的中药材中的多肽类有效成分,开展从日本蟾蜍(B.japonicus formosus)皮肤cDNA质粒文库中筛选蛋白编码基因的工作.由于后续拓展蟾蜍药用价值的研究中需要大量的实验材料,开始以中华大蟾蜍(B.gargarizans)皮肤第一链cDNA为模板,克隆其相关基因的工作.通过DNA聚合酶链式反应获得编码转胶蛋白-2(transgelin2,TAGLN2)的转录子(GenBank登录号为KF432856).该cDNA全长1 207 bp,其5′、3′端非翻译区域和开放阅读框分别为16 bp、597 bp和594 bp,编码由197个氨基酸残基组成的蛋白质,与日本蟾蜍的TAGLN2(GenBank登录号为AGQ03775.1)相比,仅一个氨基酸发生替换,与人的同源性为82%,与其他动物的同源性介于70%⁷5%.RT-PCR组织分布检测表明TAGLN2在所检测的中华大蟾蜍各器官中均有表达,在肺、肝和肾中表达量较多.这些研究结果为后续中华大蟾蜍TAGLN2的生物学功能研究以及相关药物研发提供基础数据.     

Female pied flycatchers trade between male quality and mating status in mate choice

According to mate choice theory, females should consider both male quality and mating status when choosing a mate. In birds, strong experimental evidence indicates that females prefer males with elaborate traits. No comparable evidence exists to determine whether females take male mating status into account or how they may trade between male quality and male mating status. We studied mate choice of female pied flycatchers (Ficedula hypoleuca) in outdoor aviaries where the effect of territory quality could be eliminated and where we could control which males were mated and which were unmated. We used male plumage colour as our measure of male quality. In the aviaries, focal females could easily compare males and assess their plumage colour and mating status, and resident females were prevented from attacking prospecting females because of separation in different compartments. The study provided evidence for a trade-off in mate choice. Females may compromise by choosing an already mated male if he is more brightly coloured and, presumably, of higher quality than available unmated males. The study did not support the idea that polygyny is based on male deception of females, but the results were consistent with the female aggression hypothesis.     

An experimental test of condition-dependent male and female mate choice in zebra finches

In mating systems with social monogamy and obligatory bi-parental care, such as found in many songbird species, male and female fitness depends on the combined parental investment. Hence, both sexes should gain from choosing mates in high rather than low condition. However, theory also predicts that an individual's phenotypic quality can constrain choice, if low condition individuals cannot afford prolonged search efforts and/or face higher risk of rejection. In systems with mutual mate choice, the interaction between male and female condition should thus be a better predictor of choice than either factor in isolation. To address this prediction experimentally, we manipulated male and female condition and subsequently tested male and female mating preferences in zebra finches Taeniopygia guttata, a songbird species with mutual mate choice and obligatory bi-parental care. We experimentally altered phenotypic quality by manipulating the brood size in which the birds were reared. Patterns of association for high- or low-condition individuals of the opposite sex differed for male and female focal birds when tested in an 8-way choice arena. Females showed repeatable condition-assortative preferences for males matching their own rearing background. Male preferences were also repeatable, but not predicted by their own or females' rearing background. In combination with a brief review of the literature on condition-dependent mate choice in the zebra finch we discuss whether the observed sex differences and between-studies differences arise because males and females differ in context sensitivity (e.g. male-male competition suppressing male mating preferences), sampling strategies or susceptibility to rearing conditions (e.g. sex-specific effect on physiology). While a picture emerges that juvenile and current state indeed affect preferences, the development and context-dependency of mutual state-dependent mate choice warrants further study.