Outbred embryos rescue inbred half-siblings in mixed-paternity broods of live-bearing females

Females commonly mate with more than one male, and polyandry has been shown to increase reproductive success in many species. Insemination by multiple males shifts the arena for sexual selection from the external environment to the female reproductive tract, where sperm competition or female choice of sperm could bias fertilization against sperm from genetically inferior or genetically incompatible males. Evidence that polyandry can be a strategy for avoiding incompatibility comes from studies showing that inbreeding cost is reduced in some egg-laying species by postcopulatory mechanisms that favour fertilization by sperm from unrelated males. In viviparous (live-bearing) species, inbreeding not only reduces offspring genetic quality but might also disrupt feto-maternal interactions that are crucial for normal embryonic development. Here we show that polyandry in viviparous pseudoscorpions reduces inbreeding cost not through paternity-biasing mechanisms favouring outbred offspring, but rather because outbred embryos exert a rescuing effect on inbred half-siblings in mixed-paternity broods. The benefits of polyandry may thus be more complex for live-bearing females than for females that lay eggs.     

Rapid evolution of reproductive barriers driven by sexual conflict

A growing amount of experimental data indicates extremely rapid evolution of traits and proteins related to fertilization in many diverging taxa. These data come from studies of sperm or pollen competition between closely related species, and from molecular studies of fertilization proteins. The positive selection for evolutionary novelty that appears to be acting on fertilization systems seems paradoxical because successful reproduction requires the close matching of female and male traits. It has been suggested that perpetual coevolution between the sexes can result from sexual conflict in mating. Sexual conflict occurs when characteristics that enhance the reproductive success of one sex reduce the fitness of the other sex. Numerous examples of sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating have been discussed in detail. The potential for coevolution due to such conflict has been evaluated experimentally. Here I develop a simple mathematical model describing coevolutionary dynamics of male and female traits involved in reproduction. The model shows that continual change in such traits at a constant speed is expected whenever females (or eggs) experience fitness loss from having too many compatible males (or sperms). The plausibility of runaway coevolution increases with increasing population size. Rapid evolution of reproductive barriers driven by sexual conflict may explain increased speciation rates after colonization of new habitats ('adaptive radiation') and high species richness in resource-rich environments.     

Mutual mate choice in the Asiatic toad, Bufo gargarizans, exerts stabilizing selection on body size

Sexual selection is critical to both reproduction and evolution.The effects of male–male competition and female choice regarding body size have been examined in a large number of taxa,including toad species.Males and females have different optimal reproductive strategies,achieving breeding advantages in discrepant ways.Further,the relative contributions of intra-and inter-sexual size selection vary among species.Thus,to understand the mechanisms affecting mating success,it is important to consider both male–male and male–female interactions simultaneously and elucidate their interrelationship.In this study,we measured body sizes of all mated and unmated individuals in a population of Asiatic toad(Bufo gargarizans)and counted fertilized eggs of several clutches.Based on correlation and regression techniques,we tested for female choice and intra-sexual competition among males relative to body size gradients,and we compared the relative importance of these two processes for mating success.Our results reveal that male–male competition and female choice simultaneously contribute to sexual selection in toads.Furthermore,both interactions are most intense among smaller toads.The synergistic trends of male–male competition and female choice support the mutual mate choice hypothesis and works to stabilize body size in B.gargarizans.Normal distributions of breeding success relative to body size were detected for both sexes,suggesting that medium-sized individuals enjoy a reproductive advantage in the population studied.     

基于SSR分子标记检测褐飞虱交配次数及性选择

为探明褐飞虱交配次数和性选择的生殖行为特征,构建了褐飞虱生物型1和生物型Y的近交系,筛选了在不同近交系之间存在明显差异的9个SSR (Simple Sequence Repeats)分子标记用于亲子鉴定.在雌虫交配次数试验中,观察并分子鉴定到23头成功交配的雌虫,其中19头雌虫一生仅进行1次交配,4头雌虫一生进行了2次交配,故褐飞虱雌虫是以单次交配为主、2次交配为辅的混合型交配策略.在性选择分析中,首先,性别内选择试验观察并鉴定到了23头交配成功的雄虫,其中18头生物型Y雄虫选择与雌虫进行交配;其次,性别间选择试验观察并鉴定到了83%生物型Y雄虫选择与雌虫进行交配.结果表明:在性选择行为中,生物型Y雄虫具有更强的竞争优势.     

Female mimicry in garter snakes

In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry', whereby males assume a female-like morphology or mimic female behaviour patterns. In some species males mimic both female morphology and behaviour. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5-17 males were observed formed around these individual attractive males, which we have termed 'she-males'. In competitive mating trails, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.     

Directional postcopulatory sexual selection revealed by artificial insemination

Postcopulatory sexual selection comprises both sperm competition, where the sperm from different males compete for fertilization, and cryptic female choice, where females bias sperm use in favour of particular males. Despite intense current interest in both processes as potential agents of directional sexual selection, few studies have attributed the success of attractive males to events that occur exclusively after insemination. This is because the interactions between pre- and post-insemination episodes of sexual selection can be important sources of variation in paternity. The use of artificial insemination overcomes this difficulty because it controls for variation in male fertilization success attributable to the female's perception of male quality, as well as effects due to mating order and the relative contribution of sperm from competing males. Here, we adopt this technique and show that in guppies, when equal numbers of sperm from two males compete for fertilization, relatively colourful individuals achieve greater parentage than their less ornamented counterparts. This finding indicates that precopulatory female mating preferences can be reinforced exclusively through postcopulatory processes occurring at a physiological level. Our analysis also revealed that relatively small individuals were advantaged in sperm competition, suggesting a possible trade-off between sperm competitive ability and body growth.     

Sophisticated sperm allocation in male fowl

When a female is sexually promiscuous, the ejaculates of different males compete for the fertilization of her eggs; the more sperm a male inseminates into a female, the more likely he is to fertilize her eggs. Because sperm production is limited and costly, theory predicts that males will strategically allocate sperm (1) according to female promiscuity, (2) saving some for copulations with new females, and (3) to females producing more and/or better offspring. Whether males allocate sperm in all of these ways is not known, particularly in birds where the collection of natural ejaculates only recently became possible. Here we demonstrate male sperm allocation of unprecedented sophistication in the fowl Gallus gallus. Males show status-dependent sperm investment in females according to the level of female promiscuity; they progressively reduce sperm investment in a particular female but, on encountering a new female, instantaneously increase their sperm investment; and they preferentially allocate sperm to females with large sexual ornaments signalling superior maternal investment. Our results indicate that female promiscuity leads to the evolution of sophisticated male sexual behaviour.     

Parthenogenesis in Komodo dragons

Parthenogenesis, the production of offspring without fertilization by a male, is rare in vertebrate species, which usually reproduce after fusion of male and female gametes. Here we use genetic fingerprinting to identify parthenogenetic offspring produced by two female Komodo dragons (Varanus komodoensis) that had been kept at separate institutions and isolated from males; one of these females subsequently produced additional offspring sexually. This reproductive plasticity indicates that female Komodo dragons may switch between asexual and sexual reproduction, depending on the availability of a mate--a finding that has implications for the breeding of this threatened species in captivity. Most zoos keep only females, with males being moved between zoos for mating, but perhaps they should be kept together to avoid triggering parthenogenesis and thereby decreasing genetic diversity.     

衢州中国石龙子形态特征和雌体繁殖输出

通过报道浙江衢州中国石龙子成体形态特征的两性异形和雌体繁殖输出，测定了雌雄两性个体的体长、体重、头长和头宽、附肢长和腹长，除腹长无显著两性差异外，其他形态特征均表现为雄性个体大于雌性个体。衢州种群雌体年产单窝卵，平均窝卵数，窝卵重和平均卵重分别为16．8，8．767g和0．589g．     

Sexual swellings advertise female quality in wild baboons

The females of many Old World primate species produce prominent and conspicuous swellings of the perineal skin around the time of ovulation. These sexual swellings have been proposed to increase competition among males for females or to increase the likelihood of a female getting fertilized, by signalling either a female's general reproductive status, or the timing of her ovulation. Here we show that sexual swellings in wild baboons reliably advertise a female's reproductive value over her lifetime, in accordance with a theoretical model of honest signalling. Females with larger swellings attained sexual maturity earlier, produced both more offspring and more surviving offspring per year than females with smaller swellings, and had a higher overall proportion of their offspring survive. Male baboons use the size of the sexual swelling to determine their mating effort, fighting more aggressively to consort females with larger swellings, and spending more time grooming these females. Our results document an unusual case of a sexually selected ornament in females, and show how males, by mating selectively on the basis of the size of the sexual swelling, increase their probability of mating with females more likely to produce surviving offspring.     

Unusually dynamic sex roles in a fish

Sex roles are typically thought of as being fixed for a given species. In most animals males compete for females, whereas the females are more reluctant to mate. Therefore sexual selection usually acts most strongly on males. This is explained by males having a higher potential reproductive rate than females, leading to more males being sexually active (a male-biased operational sex ratio). However, what determines sex roles and the strength of sexual selection is a controversial and much debated question. In this large-scale field study, we show a striking temporal plasticity in the mating competition of a fish (two-spotted goby, Gobiusculus flavescens). Over the short breeding season fierce male-male competition and intensive courtship behaviour in males were replaced by female-female competition and actively courting females. Hence, sex role reversal occurred rapidly. This is the first time that a shift in sex roles has been shown in a vertebrate. The shift might be explained by a large decline in male abundance, strongly skewing the sex ratio towards females. Notably, the sex role reversal did not occur at an equal operational sex ratio, contrary to established sex role theory.     

Female mating bias results in conflicting sex-specific offspring fitness

Indirect-benefit models of sexual selection assert that females gain heritable offspring advantages through a mating bias for males of superior genetic quality. This has generally been tested by associating a simple morphological quality indicator (for example, bird tail length) with offspring viability. However, selection acts simultaneously on many characters, limiting the ability to detect significant associations, especially if the simple indicator is weakly correlated to male fitness. Furthermore, recent conceptual developments suggest that the benefits gained from such mating biases may be sex-specific because of sexually antagonistic genes that differentially influence male and female reproductive ability. A more suitable test of the indirect-benefit model would examine associations between an aggregate quality indicator (such as male mating success) and gender-specific adult fitness components, under the expectation that these components may trade off. Here, we show that a father's mating success in the cricket, Allonemobius socius, is positively genetically correlated with his son's mating success but negatively with his daughter's reproductive success. This provides empirical evidence that a female mating bias can result in sexually antagonistic offspring fitness.     

变色沙蜥繁殖的研究

作者通过研究证明变色沙蜥Ｐｈｒｙｎｏｃｅｐｈａｌｕｓ ｖｅｒｓｉｃｏｌｏｒ的繁殖活动具有明显的季节性。雄晰性成熟时最小吻－肛长为４５ｍｍ，吻－肛长大的雄晰在一年中成熟精子出现早且维持时间长。雌蜥性成熟时的最小吻－肛长为４１ｍｍ，产卵期为５月末至７月末，每只雌性成蜥每年产卵一次，吻－肛长大的雌蜥产卵多而大且比吻－肛长小的雌晰产卵早。     

Behavioural ecology: transient sexual mimicry leads to fertilization

Sexual mimicry among animals is widespread, but does it impart a fertilization advantage in the widely accepted 'sneak-guard' model of sperm competition? Here we describe field results in which a dramatic facultative switch in sexual phenotype by sneaker-male cuttlefish leads to immediate fertilization success, even in the presence of the consort male. These results are surprising, given the high rate at which females reject copulation attempts by males, the strong mate-guarding behaviour of consort males, and the high level of sperm competition in this complex mating system.     

Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.     

Sexual conflict reduces offspring fitness in zebra finches

Parental care is often costly; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised.     

Decisions about parental care in response to perceived paternity

Evolutionary ecologists are attempting to explain how parents make behavioural decisions about how much care to provide to their young. Theory predicts that when genetic relatedness to young is decreased by cuckoldry, for example, parents should reduce their care in favour of alternative broods that provide greater reproductive success. Experimental manipulation of perceived paternity has been used to test the theory, but such studies have generated mixed results. Some manipulations can fail to alter a parent's perceived paternity, whereas others may directly affect parental behaviour when, for instance, the manipulation involves capturing the parent. No study has demonstrated parental care adjustment in a manner uncomplicated by experimental design or life history correlates. Here I test the theory using the fact that nest-tending parental male bluegill sunfish (Lepomis macrochirus) can assess their paternity using both the visual presence of parasitic cuckolder males during spawning, and olfactory cues released by newly hatched eggs. By manipulating both types of cues I show that parental males dynamically adjust their parental care, favouring broods that are apparently most closely related. These results confirm the importance of genetic relatedness in parental care decision-making.     

Sympatric speciation by sexual selection

There is increasing evidence for the process of sympatric speciation, in which reproductive isolation of species occurs without physical isolation. Theoretical models have focused on disruptive natural selection as the crucial pressure for splitting a species. Here we report the theoretical finding that sympatric speciation may be caused by sexual selection even without disruptive natural selection. Specifically, we show that variation in a male secondary sexual character with two conspicuous extremes and the corresponding variance in female mating preference around no preference may jointly evolve into bimodal distributions with increasing modal divergence of the male and female traits, pulling a population apart into two prezygotically isolated populations. This mode of speciation, driven by two runaway processes in different directions, is promoted by an increase in the efficiency of females in discriminating among males or a decrease in the cost of male conspicuousness, indicating that sympatric speciation may occur more readily if barrier-free or predator-free conditions arise. Although even a slight cost of female preference would cancel the runaway process of sexual selection, it would not cancel the divergent runaway processes of sympatric speciation.     

Mating advantage of rare males in models of sexual selection

Models of sexual selection in polygynous species of animals have been derived on the assumption that some females have preferences to mate with males with particular genotypes. The mating advantage gained by the males is always frequency-dependent because the preferred males take part in the same number of preferential matings when they are rare as when they are common; individually therefore, they mate more often when they are rare. Frequency-dependent sexual selection has been demonstrated in many experiments with Drosophila: rare males take part in a higher proportion of matings than their frequency as available mates. Ehrman and Spiess explained this phenomenon by frequency-dependence either in female preference or in male courtship. This explanation, which is difficult to interpret in behavioural terms, may not be necessary, however, because constant female preferences would entail frequency-dependent selection among the males. I show here that a simple model of constant preferences for particular phenotypes or genotypes is sufficient to explain a large body of data on frequency-dependent sexual selection in Drosophila.     

Evidence that sensory traps can evolve into honest signals

Conventional models explaining extreme sexual ornaments propose that these reflect male genetic quality or are arbitrary results of genetic linkage between female preference and the ornament. The chase-away model emphasizes sexual conflict: male signals attract females because they exploit receiver biases. As males gain control of mating decisions, females may experience fitness costs through suboptimal mating rates or post-copulatory exploitation. Elaboration of male signals is expected if females increase their response threshold to resist such exploitation. If ornaments target otherwise adaptive biases such as feeding responses, selection on females might eventually separate sexual and non-sexual responses to the signal. Here we show that the terminal yellow band (TYB) of several Goodeinae species evokes both feeding and sexual responses; sexual responsiveness phylogenetically pre-dates the expression of the TYB in males and is comparable across taxa, yet feeding responsiveness decreases in species with more elaborated TYBs. Displaying a TYB is costly, and thus provides an example where a trait arose as a sensory trap but has evolved into an honest signal.