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.     

Courtship raises male fertilization success through post-mating sexual selection in a spider

Courtship is well known for its positive effects on mating success. However, in polyandrous species, sexual selection continues to operate after copulation. Cryptic female choice is expected under unpredictable mating rates in combination with sequential mate encounters. However, there are very few accounts of the effects of courtship on cryptic female choice, and the available evidence is often correlative.Mature Argiope bruennichi females are always receptive and never attack or reject males before mating, although sexual cannibalism after mating occurs regularly. Still, males usually perform an energetic vibratory display prior to copulation. We tested the hypothesis that beneficial effects of courtship arise cryptically, during or after mating, resulting in increased paternity success under polyandry. Manipulating courtship duration experimentally, we found that males that mated without display had a reduced paternity share even though no differences in post-copulatory cannibalism or copulation duration were detected. This suggests that the paternity advantage associated with courtship arose through female-mediated processes after intromission, meeting the definition of cryptic female choice.     

Masturbation in captive Hylobates (gibbons)

Masturbation was observed in 9 of 52 captive adult Hylobates (gibbons) over a period of 17 years at the International Center for Gibbon Studies (ICGS). Four females and 5 males masturbated with varying degrees of regularity. The behavior may be related to a disruption in early rearing experiences of Hylobates. This is the first report on masturbation in these animals and documents that this behavior occurs infrequently in captive Hylobates. © 1994 Wiley-Liss, Inc.     

A JOINT INDEX FOR THE INTENSITY OF SEX‐SPECIFIC SELECTION

A growing body of experimental and field data shows that selective pressures often differ between males and females. Surprisingly, to date, little attempt has been made to formalize a metric expressing the relative behavior of directional selection in the two sexes. We propose an index that describes the extent to which concordant or antagonistic selection is operating between the sexes for a given trait. This joint index could prove especially useful for the study of intralocus sexual conflict and the evolution of sexual dimorphism, providing a common scale to directly compare different traits within or among taxonomic levels, and allowing an assessment on how common sexually antagonistic selection might be in extant populations.     

A comparative study on the evolution of reversed size dimorphism in monogamous waders

Sexual dimorphism in size is common in birds. Males are usually larger than females, although in some taxa reversed size dimorphism (RSD) predominates. Whilst direct dimorphism is attributed to sexual selection in males giving greater reproductive access to females, the evolutionary causes of RSD are still unclear. Four different hypotheses could explain the evolution of RSD in monogamous birds: (1) The ‘energy storing’ hypothesis suggests that larger females could accumulate more reserves at wintering or refuelling areas to enable an earlier start to egg laying. (2) According to the ‘incubation ability’ hypothesis, RSD has evolved because large females can incubate more efficiently than small ones. (3) The ‘parental role division’ hypothesis suggests that RSD in monogamous waders has evolved in species with parental role division and uniparental male care of the chicks. It is based on the assumption that small male size facilitates food acquisition in terrestrial habitats where chick rearing takes place and that larger females can accumulate more reserves for egg laying in coastal sites. (3) The ‘display agility’ hypothesis suggests that small males perform better in acrobatic displays presumably involved in mate choice and so RSD may have evolved due to female preference for agile males. I tested these hypotheses in monogamous waders using several comparative methods. Given the current knowledge of the phylogeny of this group, the evolutionary history of waders seems only compatible with the hypothesis that RSD has evolved as an adaptation for increasing display performance in males. In addition, the analysis of wing shape showed that males of species with acrobatic flight displays had wings with higher aspect ratio (wing span/²wing area) than non-acrobatic species, which probably increases flight manoeuvrability during acrobatic displays. In species with acrobatic displays males also had a higher aspect ratio than females although no sexual difference was found in non-acrobatic species. These results suggest that acrobatic flight displays could have produced changes in the morphology of some species and suggest the existence of selection favouring higher manoeuvrability in species with acrobatic flight displays. This supports the validity of the mechanisms proposed by the ‘display agility’ hypothesis to explain the evolution of RSD in waders.     

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.     

SEX-LINKAGE OF SEXUALLY ANTAGONISTIC GENES IS PREDICTED BY FEMALE, BUT NOT MALE, EFFECTS IN BIRDS

Evolutionary theory predicts that sexually antagonistic loci will be preferentially sex-linked, and this association can be empirically testes with data on sex-biased gene expression with the assumption that sex-biased gene expression represents the resolution of past sexual antagonism. However, incomplete dosage compensating mechanisms and meiotic sex chromosome inactivation have hampered efforts to connect expression data to theoretical predictions regarding the genomic distribution of sexually antagonistic loci in a variety of animals. Here we use data on the underlying regulatory mechanism that produce expression sex-bias to test the genomic distribution of sexually antagonistic genes in chicken. Using this approach, which is free from problems associated with the lack of dosage compensation in birds, we show that female-detriment genes are significantly overrepresented on the Z chromosome, and female-benefit genes underrepresented. By contrast, male-effect genes show no over- or underrepresentation on the Z chromosome. These data are consistent with a dominant mode of inheritance for sexually antagonistic genes, in which male-benefit coding mutations are more likely to be fixed on the Z due to stronger male-specific selective pressures. After fixation of male-benefit alleles, regulatory changes in females evolve to minimize antagonism by reducing female expression.     

Sexual selection targets cetacean pelvic bones

Male genitalia evolve rapidly, probably as a result of sexual selection. Whether this pattern extends to the internal infrastructure that influences genital movements remains unknown. Cetaceans (whales and dolphins) offer a unique opportunity to test this hypothesis: since evolving from land‐dwelling ancestors, they lost external hind limbs and evolved a highly reduced pelvis that seems to serve no other function except to anchor muscles that maneuver the penis. Here, we create a novel morphometric pipeline to analyze the size and shape evolution of pelvic bones from 130 individuals (29 species) in the context of inferred mating system. We present two main findings: (1) males from species with relatively intense sexual selection (inferred by relative testes size) tend to evolve larger penises and pelvic bones compared to their body length, and (2) pelvic bone shape has diverged more in species pairs that have diverged in inferred mating system. Neither pattern was observed in the anterior‐most pair of vertebral ribs, which served as a negative control. This study provides evidence that sexual selection can affect internal anatomy that controls male genitalia. These important functions may explain why cetacean pelvic bones have not been lost through evolutionary time.     

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.     

SEXUAL DICHROMATISM IN BIRDS: IMPORTANCE OF NEST PREDATION AND NEST LOCATION FOR FEMALES VERSUS MALES

Examinations of variation in plumage dichromatism in birds have focused on male plumage brightness and largely neglected variation in female plumage brightness. Nest predation previously was concluded to constrain male brightness and thereby reduce dimorphism in ground-nesting birds based on an incorrect assumption that nest predation is greater for ground nests. Correlations of plumage brightness and dichromatism with nest predation have never been tested directly and we do so here with data for warblers (Parulinae) and finches (Carduelinae). We show that male plumage brightness varies among nest heights, but in a pattern that is not correlated with nest predation. Female plumage brightness also varies among nest heights, but in a pattern that differs from males, and one in which variation in female plumage brightness was negatively correlated with nest predation. These results suggest that nest predation may place greater constraints on female than male plumage brightness, at least in taxa where only females incubate eggs and brood young. These results also show that female plumage patterns vary at least partly independently of male patterns and emphasize the need to include consideration of both female and male plumage variation in tests of plumage dimorphism. Plumage dimorphism differs between ground and off-ground nesters as previously described and, if anything, the relationship between plumage dimorphism and nest predation was positive rather than negative as previously argued.     

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.     

A PHYLOGENETIC PERSPECTIVE ON THE EVOLUTION OF SEXUAL DICHROMATISM IN TANAGERS (THRAUPIDAE): THE ROLE OF FEMALE VERSUS MALE PLUMAGE

The evolution of sexual dichromatism in tanagers (family Thraupidae) was studied from a phylogenetic perspective using a molecular-based phylogeny. Mapping patterns of sexual dimorphism in plumage onto the phylogeny reveals that changes in female plumage occur more frequently than changes in male plumage. Possible explanations for this pattern include sexual selection acting on female plumage and natural selection for background matching. The results of this study and other recent phylogenetic and comparative studies suggest that factors affecting female plumage are important in shaping patterns of sexual dimorphism.     

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.     

Genital damage in the orb-web spider Argiope bruennichi (Araneae: Araneidae) increases paternity success

The morphology of male genitalia often suggests functions besidessperm transfer that may have evolved under natural or sexualselection. In several species of sexually cannibalistic spiders,males damage their paired genitalia during mating, limitingthem to one copulation per pedipalp. Using a triple-mating experiment,we tested if genital damage in the orb-web spider Argiope bruennichiincreases male fitness either through facilitating his escapefrom an aggressive female or by obstructing the female's inseminationducts against future copulation attempts from other males. Wefound no survival advantage for males damaging their pedipalps;however, copulations into a previously used insemination ductwere significantly shorter when the previous male had left partsof his genitalia inside the insemination duct. Because copulationduration determines paternity in this species, our result suggeststhat male genital damage in A. bruennichi is sexually selected.By breaking off parts of their intromittent organs inside avirgin female, males can reduce sperm competition and therebyincrease their paternity success.     

大蹼铃蟾的两性异形

2018年6—8月,测量采自云南省昆明市金殿水库后山的71只(47♂,24♀)大蹼铃蟾Bombina maxima成体的体长、头长、头宽等15项形态特征指标并检验该物种的两性异形。结果表明:雄性平均体长为53.54 mm±1.14 mm,雌性平均体长为52.74 mm±1.45 mm,雄性与雌性平均体长比为1.015,两性异性指数为0.01;大蹼铃蟾的体长、体质量与性别之间的差异无统计学意义;除了雌性的眼间距外,其余13项形态特征与体长均有极显著相关性;以体长为协变量的协方差分析结果显示,大蹼铃蟾的头长、吻长、前臂宽、腿或后肢全长、胫长、胫宽和跗足长在两性间的差异有高度统计学意义;雄性的这7项形态特征随体长的生长速率大于雌性。性选择假说能解释大蹼铃蟾的两性异形现象。     

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。     

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.     

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.