Sex‐specific recombination rates and allele frequencies affect the invasion of sexually antagonistic variation on autosomes

The introduction and persistence of novel, sexually antagonistic alleles can depend upon factors that differ between males and females. Understanding the conditions for invasion in a two‐locus model can elucidate these processes. For instance, selection can act differently upon the sexes, or sex linkage can facilitate the invasion of genetic variation with opposing fitness effects between the sexes. Two factors that deserve further attention are recombination rates and allele frequencies – both of which can vary substantially between the sexes. We find that sex‐specific recombination rates in a two‐locus diploid model can affect the invasion outcome of sexually antagonistic alleles and that the sex‐averaged recombination rate is not necessarily sufficient to predict invasion. We confirm that the range of permissible recombination rates is smaller in the sex benefitting from invasion and larger in the sex harmed by invasion. However, within the invasion space, male recombination rate can be greater than, equal to or less than female recombination rate in order for a male‐benefit, female‐detriment allele to invade (and similarly for a female‐benefit, male‐detriment allele). We further show that a novel, sexually antagonistic allele that is also associated with a lowered recombination rate can invade more easily when present in the double heterozygote genotype. Finally, we find that sexual dimorphism in resident allele frequencies can impact the invasion of new sexually antagonistic alleles at a second locus. Our results suggest that accounting for sex‐specific recombination rates and allele frequencies can determine the difference between invasion and non‐invasion of novel, sexually antagonistic alleles in a two‐locus model.     

性选择与性冲突理论在植物繁殖生态学中的应用与进展

性选择与性冲突是植物繁殖性状多样性及性系统演化的重要动力, 二者密切相关却又有所区别, 理解它们的作用机制及其影响对于植物繁殖生态学的研究具有重要意义。当前, 性选择与性冲突理论在植物繁殖生态学中的运用已取得长足进展, 但国内相关研究较少, 对该领域关注不够。因此, 该文对该领域的基本理论和研究进展进行了综述。首先, 阐述性选择与性冲突理论在植物研究中的发展及其运用基础; 其次, 分别从授粉前和授粉后两个阶段详细介绍性选择与性冲突在有花植物繁殖过程中的作用机制及其影响, 并指出环境因素对它们所产生的影响; 最后, 对当前研究存在的不足及该领域未来的研究方向进行总结和展望。希望以此增强人们对性选择和性冲突理论的认识, 促进其在植物繁殖生态学中的运用与发展。     

Perspective: sexual conflict and sexual selection: chasing away paradigm shifts

Abstract.— Traditional models of sexual selection propose that partner choice increases both average male and average female fitness in a population. Recent theoretical and empirical work, however, has stressed that sexual conflict may be a potent broker of sexual selection. When the fitness interests of males and females diverge, a reproductive strategy that increases the fitness of one sex may decrease the fitness of the other sex. The chase-away hypothesis proposes that sexual conflict promotes sexually antagonistic, rather than mutualistic, coevolution, whereby manipulative reproductive strategies in one sex are counteracted by the evolution of resistance to such strategies in the other sex. In this paper, we consider the criteria necessary to demonstrate the chase-away hypothesis. Specifically, we review sexual conflict with particular emphasis on the chase-away hypothesis; discuss the problems associated with testing the predictions of the chase-away hypothesis and the extent to which these predictions and the predictions of traditional models of sexual selection are mutually exclusive; discuss misconceptions and mismeasures of sexual conflict; and suggest an alternative approach to demonstrate sexual conflict, measure the intensity of sexually antagonistic selection in a population, and elucidate the coevolutionary trajectories of the sexes.     

Costs and benefits of polyandry in a sexually cannibalistic mantis

Mating with more than one male often provides direct or indirect benefits to female fitness but can also increase the chance of injury and death. Costs of mating are expected to increase linearly with increasing mating number. But how such costs interact with benefits to determine the net payoff of mating multiply is not well understood. Using the highly cannibalistic Springbok mantis, Miomantis caffra, a species where females are stabbed in the abdomen by males during violent premating struggles that males initiate to avoid being cannibalized, we took an experimental approach to assess the economics of polyandry under the risk of external, male-inflicted injury. We predicted that females that mate multiply would be more likely to show abdominal injuries, have higher prereproductive mortality, produce fewer offspring and be more likely to engage in pre-mating cannibalism to avoid unwanted matings. In line with our predictions, we found that the likelihood of abdominal injury was highest among females that mated at least once, and prereproductive death was highest among females that mated twice or three times. Virgin females completely avoided these costs and produced some offspring parthenogenetically but not enough to provide a net benefit. Although mating was better than not mating, there was no singularly optimal mating number: females that mated once and three times produced similarly high numbers of offspring from the first ootheca, which resulted in an intermediate trough in offspring production at two matings. We also found little evidence that cannibalism was deployed as a mate-avoidance strategy: females consistently attacked and consumed males regardless of how many times they mated or how long they were housed with males. Our results suggest the possibility of two distinct mating strategies in M. caffra, where females either mate at a lower frequency to minimize costs or at a higher frequency to maximize benefits. We discuss possible explanations for this bimodal pattern in offspring production.     

Courtship song and immune function in the field cricket Gryllus bimaculatus

It has been assumed that sexual ornaments have evolved to reveal males' health and vigour for females. Choosy females may indirectly use ornaments as an indicator of the presence and effectiveness of genes for resistance against parasites. In this study we tested whether females of the Mediterranean field cricket, Gryllus bimaculatus, can use courtship song as a cue for choosing males with high immunocompetence, measured as encapsulation rate of nylon implants and lytic activity of haemolymph. We found that female crickets preferred courtship songs from males with a high encapsulation rate. Female crickets also had a tendency to prefer courtship songs with high tick rate and long high-frequency tick duration. These preferred song components were positively correlated with encapsulation rate, but negatively correlated with lytic activity of the male. In contrast to previous studies of crickets, there was no correlation between male weight and encapsulation rate or lytic activity. There is some evidence in another cricket species that the ability to encapsulate pathogens is heritable. Thus, in light of this study it seems possible that by preferring males according to their courtship song, females might benefit by increasing the parasite resistance of their offspring.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 503–510.     

Inter-sexual combat and resource allocation into body parts in the spider, Stegodyphus lineatus

Abstract.  1. Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits.
2. Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter-sexual armament.
3. In the spider Stegodyphus lineatus , males fight with females over re-mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament – the cephalothorax, may be traded-off against investment in abdomen, which is a trait that affects survival and fecundity. Pay-offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly.
4. Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high.
5. The results support the theoretical conjecture that population density affects resource allocation into inter-sexual armament and call for further research on the interaction between sexual selection and population density.     

Inter- and intrasexual dimorphism in the diving beetle Hydroporus memnonius Nicolai (Coleoptera: Dytiscidae)

Sexual conflict can drive rapid intersexual arms races, and lead to pronounced sexual dimorphism. Such dimorphism is frequent in diving beetles, where males typically possess expanded front and middle tarsi, supplied with adhesive setae to grasp females during mating, and females often have rough dorsal surfaces which hinder male attachment. In a number of species, females are dimorphic, being either smooth and male-like, or heavily sculptured dorsally. Smooth and sculptured females often have distinct biogeographies, and may be expected to be associated with specific counter-adaptations in males. The European diving beetle, Hydroporus memnonius Nicolai, includes a smooth male-like female, and a matt morph, var. castaneus Aubé, which are largely allopatric in distribution. We show that the two morphs differ in the density and intensity of their surface microreticulation, and that matt females are associated with morphologically distinct males, which have developed specific countermeasures on their tarsi, including a greater number of large adhesive setae, individually larger in area. Such males are expected to be more successful in pairing with both matt and shining females, and it is suggested that a process of population replacement, partly driven by sexual interactions, may occur where the two forms overlap in range.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 685–697.     

Intralocus sexual conflict and offspring sex ratio

Males and females frequently have different fitness optima for shared traits, and as a result, genotypes that are high fitness as males are low fitness as females, and vice versa. When this occurs, biasing of offspring sex-ratio to reduce the production of the lower-fitness sex would be advantageous, so that for example, broods produced by high-fitness females should contain fewer sons. We tested for offspring sex-ratio biasing consistent with these predictions in broad-horned flour beetles. We found that in both wild-type beetles and populations subject to artificial selection for high- and low-fitness males, offspring sex ratios were biased in the predicted direction: low-fitness females produced an excess of sons, whereas high-fitness females produced an excess of daughters. Thus, these beetles are able to adaptively bias sex ratio and recoup indirect fitness benefits of mate choice.     

Sexual dichromatism in frogs: natural selection, sexual selection and unexpected diversity

Sexual dichromatism, a form of sexual dimorphism in which males and females differ in colour, is widespread in animals but has been predominantly studied in birds, fishes and butterflies. Moreover, although there are several proposed evolutionary mechanisms for sexual dichromatism in vertebrates, few studies have examined this phenomenon outside the context of sexual selection. Here, we describe unexpectedly high diversity of sexual dichromatism in frogs and create a comparative framework to guide future analyses of the evolution of these sexual colour differences. We review what is known about evolution of colour dimorphism in frogs, highlight alternative mechanisms that may contribute to the evolution of sexual colour differences, and compare them to mechanisms active in other major groups of vertebrates. In frogs, sexual dichromatism can be dynamic (temporary colour change in males) or ontogenetic (permanent colour change in males or females). The degree and the duration of sexual colour differences vary greatly across lineages, and we do not detect phylogenetic signal in the distribution of this trait, therefore frogs provide an opportunity to investigate the roles of natural and sexual selection across multiple independent derivations of sexual dichromatism.     

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.     

Intraspecific evidence from guppies for correlated patterns of male and female genital trait diversification

The role of sexual selection in fuelling genital evolution is becoming increasingly apparent from comparative studies revealing interspecific divergence in male genitalia and evolutionary associations between male and female genital traits. Despite this, we know little about intraspecific variance in male genital morphology, or how male and female reproductive traits covary among divergent populations. Here we address both topics using natural populations of the guppy, Poecilia reticulata, a livebearing fish that exhibits divergent patterns of male sexual behaviour among populations. Initially, we performed a series of mating trials on a single population to examine the relationship between the morphology of the male's copulatory organ (the gonopodium) and the success of forced matings. Using a combination of linear measurements and geometric morphometrics, we found that variation in the length and shape of the gonopodium predicted the success of forced matings in terms of the rate of genital contacts and insemination success, respectively. We then looked for geographical divergence in these traits, since the relative frequency of forced matings tends to be greater in high-predation populations. We found consistent patterns of variation in male genital size and shape in relation to the level of predation, and corresponding patterns of (co)variation in female genital morphology. Together, these data enable us to draw tentative conclusions about the underlying selective pressures causing correlated patterns of divergence in male and female genital traits, which point to a role for sexually antagonistic selection.     

蒲河流域河流生境质量综合评价及其与水质响应关系

河流生境是河流生物赖以生存的环境,是维持河流生态完整性、维护河流健康的重要因素。本文结合蒲河流域环境特点,运用层次分析法建立了蒲河流域河流生境质量评价体系,对流域内25个河段的生境质量状况进行了综合评价,并进一步分析了河流生境综合评价指数与河流水质的相关关系。结果表明:(1)蒲河流域25个河段的生境质量状况差异显著,其中1个河段的生境质量等级为好,5个河段为较好等级,16个河段为一般等级,3个河段为较差等级。(2)生境综合评价指数与TP、NH4+-N、CODCr呈负相关,生境质量评价体系中其他指标也与水质指标具有相关性,表明生境质量是影响水质的重要因素。     

Reversal of sexual induction in Volvox carteri by ultraviolet irradiation and removal of sexual pheromone

Washing in fresh culture medium or short exposure to ultraviolet irradiation (UV) was found to reverse the action of the sexual pheromone produced by the green alga Volvox carteri. Induced gonidia which would normally form egg-bearing females formed mainly asexual individuals in response to these treatments. The UV effect is strongly dependent on the stage of the life cycle at which exposure is given. Sexual induction in this organism requires early and continuous exposure to the sexual pheromone. The mechanism by which UV reverses sexual induction is not understood, but it could be caused by inactivation of the pheromone or by inactivation of a pheromone-induced repressor of asexual characters.     

Sexual bimaturation and sexual size dimorphism in animals with asymptotic growth after maturity

Many animal taxa exhibit a positive correlation between sexual size dimorphism and sex differences in age at maturity, such that members of the larger sex mature at older ages than members of the smaller sex. Previous workers have suggested that sexual bimaturation is a product of sex differences in growth trajectories, but to date no one has tested this hypothesis. The current study uses growth-based models to study relationships between sexual size dimorphism and sexual bimaturation in species with asymptotic growth after maturity. These models show that sex differences in asymptotic size would produce sexual bimaturation even if both sexes approach their respective asymptotic sizes at the same age, mature at the same proportion of asymptotic size and have otherwise equivalent growth and maturation patterns. Furthermore, our analyses show that there are three ways to reduce sexual bimaturation in sexually size-dimorphic species: (1) higher characteristic growth rates for members of the larger sex, (2) larger size at birth, hatching or metamorphosis for members of the larger sex or (3) smaller ratio of size at maturity to asymptotic size (relative size at maturity) for members of the larger sex. Of these three options, sex differences in relative size at maturity are most common in size-dimorphic species and, in both male-larger and female-larger species, members of the larger sex frequently mature at a smaller proportion of their asymptotic size than do members of the smaller sex. Information about the growth and maturation patterns of a taxon can be used to determine relationships between sexual size dimorphism and sexual bimaturation for the members of that taxon. This process is illustrated for Anolis lizards, a genus in which both sexes exhibit the same strong correlation (r 0.97) between size at maturity and asymptotic size, and in which the relative size at maturity is inversely related to asymptotic size for both sexes. As a result, sexually size-dimorphic species of anoles exhibit the expected pattern of a smaller relative size at maturity for members of the larger sex. However, for species in this genus, sex differences in the relative size at maturity are not strong enough to produce the same age at maturity for both sexes in sexually size-dimorphic species. Members of the larger sex (usually males) are still expected to mature at older ages than members of the smaller sex in Anolis lizards.     

Mental health policies on reporting child sexual abuse and physician‐patient sexual relationships

The reporting of child sexual abuse (CSA) and physician-patient sexual relationships (PPSR) are currently the focus of professional, legal and media attention in several countries. This paper briefly reviews mental health policies on these issues and reports on a WPA survey of them. While the WPA Madrid Declaration permits breaching confidentiality for mandatory reporting of CSA and clearly prohibits PPSR, it is not known how or to what extent these policies are implemented in WPA Member Societies’ countries. It is also not known whether policies or laws exist on these topics nationally or to what extent psychiatrists and the public are aware of them. Representatives of WPA Member Societies were e-mailed a survey about issues pertaining to CSA and PPSR. Fifty-one percent of 109 countries replied. All reporting countries had laws or policies regarding the reporting of CSA, but this was often voluntary (63%) and without protection for reporting psychiatrists either by law (29%) or by Member Societies (27%). A substantial number of psychiatric leaders did not know the law (27%) or their Society’s policy (11%) on these matters. With respect to PPSR, some reporting countries lacked laws or policies about PPSR with current (17%) or past (56%) patients. Fewer than half of responding representatives believed that their Society’s members or the public were well informed about the laws and policies pertaining to CSA or PPSR. There is clearly a wide range of laws, policies and practices about CSA and PPSR in WPA Member Societies’ countries. There is a need in some countries for laws or supplemental policies to facilitate the protection of vulnerable child and adult patients through clear, mandatory reporting policies for CSA and PPSR. Mechanisms to protect and support reporting psychiatrists should also be developed where they do not already exist. There is also a need in some countries to develop strategies to improve the education of psychiatrists, trainees, and the public on these issues.     

Sexual behaviour and evolution of sexual dimorphism in body size in Jaera (Isopoda Asellota)

Individuals of the genus Jaera do not mate at random. In the species from the Mediterranean group, J. italica and. J. nordmanni, large males and medium sized females are at an advantage and their sizes are positively assorted. These effects are attributable to sexual competition between males. In the Ponlo-caspian species J. istri, no advantage of large males exists, but sexual selection could be the cause for a long passive phase prior to copulation and for normalizing selection upon female size at pairing. In the Atlantic species, J. albifrons, no selection can be ascertained.
Differential mating success in males appears as one of the causes of the evolution of sexual dimorphism in body size, which makes males larger, of equal size, or smaller than females according to the species. The reason for this reversal in dimorphism seems to differ in the two sexes. Sexual selection provides an explanation for the evolution of male size, while the interspecific changes in female length are more likely due to ecological factors.     

Sex and Weapons: Contrasting Sexual Dimorphisms in Weaponry and Aggression in Snapping Shrimp

Sexual dimorphisms in weaponry and aggression are common in species in which one sex (usually males) competes for access to mates or resources necessary for reproduction – sexually dimorphic weaponry and aggression, in other words, are frequently the result of intrasexual selection. In snapping shrimp, the major chela (snapping claw) can be a deadly weapon, and males of many species have larger chelae than females, a pattern readily interpreted as resulting from intrasexual selection. Thus, males might be expected to show more sex‐specific aggression than females, and be more aggressive overall. We tested these predictions in two species of snapping shrimp in a territorial defense context. Neither of these predictions was supported: in both species, females, but not males, engaged in sex‐specific aggression and females were more aggressive than males overall. These contrasting sexual dimorphisms – larger weaponry in males but higher aggression in females – highlight the importance of considering the function of weaponry and aggression in contexts other than direct competitions over mates. In addition, species differences in the degree of sexual dimorphism in chela size were due to differences in female, not male, chela size, and the species with greater sexual dimorphism in weaponry was significantly less aggressive overall; also, while paired and solitary males did not differ in residual chela size, for the species with greater sexual dimorphism, females carrying embryos had smaller residual chela sizes. These results suggest that understanding the sexual dimorphisms in weaponry and aggression in snapping shrimp requires understanding the relative costs and benefits of both in females as well as males.     

Interactions among mechanisms of sexual selection on male body size and head shape in a sexually dimorphic fly

Abstract Darwin envisaged male-male and male-female interactions as mutually supporting mechanisms of sexual selection, in which the best armed males were also the most attractive to females. Although this belief continues to predominate today, it has been challenged by sexual conflict theory, which suggests that divergence in the interests of males and females may result in conflicting sexual selection. This raises the empirical question of how multiple mechanisms of sexual selection interact to shape targeted traits. We investigated sexual selection on male morphology in the sexually dimorphic fly Prochyliza xanthostoma , using indices of male performance in male-male and male-female interactions in laboratory arenas to calculate gradients of direct, linear selection on male body size and an index of head elongation. In male-male combat, the first interaction with a new opponent selected for large body size but reduced head elongation, whereas multiple interactions with the same opponent favored large body size only. In male-female interactions, females preferred males with relatively elongated heads, but male performance of the precopulatory leap favored large body size and, possibly, reduced head elongation. In addition, the amount of sperm transferred (much of which is ingested by females) was an increasing function of both body size and head elongation. Thus, whereas both male-male and male-female interactions favored large male body size, male head shape appeared to be subject to conflicting sexual selection. We argue that conflicting sexual selection may be a common result of divergence in the interests of the sexes.