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1.
    
In this paper, I consider the criteria necessary to demonstrate the postcopulatory ability of females to favor the sperm of one conspecific male over another, that is, sperm choice. In practice it is difficult to distinguish between sperm competition and sperm choice, and sperm choice can be demonstrated only if the effects of sperm competition can be controlled. Few studies have used experimental protocols that do this, so evidence for sperm choice is limited. Moreover, in those studies in which sperm choice occurs, it does so to avoid incompatible genetic combinations and is therefore unlikely to result in directional sexual selection.  相似文献   

2.
We review possible effects of sexual selection upon sperm morphology, and sexual skin morphology, in primates. Comparative morphometric studies, involving 31 species representing 21 primate genera, revealed a positive relationship between volume of the sperm midpiece, occurrences of multiple partner matings by females, and large relative testes sizes, which indicate sperm competition. The midpiece houses the mitochondria required to power sperm motility. Hence, sperm competition may have influenced the evolution of increased mitochondrial loading in species where females mate with multiple partners during the fertile period. Females of some Old World monkey species and female chimpanzees exhibit large estrogen-dependent sexual skin swellings during the follicular phase of the menstrual cycle. Studies of mandrills support the conclusion that swellings act primarily as sexually attractive, graded signals and that swelling size may indicate current reproductive quality. Measurements of the genitalia in chimpanzees indicate a secondary function for female swellings. The swelling increases the operating depth of the female's vagina by 50% during the fertile phase of her cycle. Males have evolved long, filiform penes capable of placing sperm close to the os cervix during competitive multipartner matings. This may exemplify how morphologic specializations in females can influence the coevolution of advantageous genitalic specializations in males: the phenomenon that Eberhard (1985) dubbed cryptic female choice.  相似文献   

3.
    
In species with limited opportunities for pre‐ejaculatory sexual selection (behavioural components), post‐ejaculatory mechanisms may provide opportunities for mate choice after gametes have been released. Recent evidence from a range of taxa has revealed that cryptic female choice (i.e., female‐mediated differential fertilization bias), through chemical cues released with or from eggs, can differentially regulate the swimming characteristics of sperm from various males and ultimately determine male fertilization success under sperm competition. We assessed the potential role that such female‐modulated chemical cues play in influencing sperm swimming characteristics in beach‐spawning capelin (Mallotus villosus), an externally fertilizing fish that mates as couples (one male and one female) or threesomes (two males and one female) with presumably limited opportunities for pre‐ejaculatory sexual selection. We assayed sperm swimming characteristics under varying doses and donor origins of egg cues and also examined the possibility of assortative mating based on body size. We found mating groups were not associated by size, larger males did not produce better quality ejaculates, and egg cues (regardless of dosage or donor identity) did not influence sperm swimming characteristics. Our findings suggest that intersexual pre‐ejaculatory sexual selection and cryptic female choice mediated by female chemical cues are poorly developed in capelin, possibly due to unique natural selection constraints on reproduction.  相似文献   

4.
    
Polyandry, where multiple mating by females results in the temporal and spatial overlap of ejaculates from two or more males, is taxonomically widespread and occurs in varying frequencies within and among species. In decapods (crabs, lobsters, crayfish, and prawns), rates of polyandry are likely to be variable, but the extent to which patterns of multiple paternity reflect multiple mating, and thus are shaped by postmating processes that bias fertilization toward one or a subset of mated males, is unclear. Here, we use microsatellite markers to examine the frequency of multiple mating (the presence of spermatophores from two or more males) and patterns of paternity in wild populations of western rock lobster (Panulirus cygnus). Our data confirm that >45% of females had attached spermatophores arising from at least two males (i.e., confirming polyandry), but we found very limited evidence for multiple paternity; among 24 clutches sampled in this study, only two arose from fertilizations by two or more males. Single inferred paternal genotypes accounted for all remaining progeny genotypes in each clutch, including several instances when the mother had been shown to mate with two or more males. These findings highlight the need for further work to understand whether polyandry is adaptive and to uncover the mechanisms underlying postmating paternity biases in this system.  相似文献   

5.
    
In order to evaluate selection of male morphological traits during copulation, a laboratory experiment was performed with the promiscuous seedbug Lygaeus simulans. Three male traits suspected as putative targets of selection were measured: weight, fluctuating asymmetry of a measure on the forewings, and length of a conspicuous genital structure, the processus gonopori. As fitness measures we considered total fecundity (number of fertilized eggs), insemination and fertilization success (established if a female laid fertilized eggs after copulation), and the interval between copulation and oviposition. Eighty-four males were allowed a single copulation with one virgin female each. Out of 67 copulations, 27 (40.2%) resulted in fertilized eggs and the oviposition latency ranged from 6 to 26 days. Regressions of male traits on the fitness measures showed significant phenotypical selection of two male traits: (1) males of average weight are more likely to achieve fertilization and (2) the oviposition latency was shorter for males with lower asymmetry. The copulation-oviposition interval may be especially important for male fertilization success because Lygaeus males perform copulatory mate guarding and the last male copulating with a female fertilizes most of the eggs. No selection of the genitalic trait was detected.  相似文献   

6.
    
When females mate with multiple partners within a single reproductive cycle, sperm from rival males may compete for fertilization of a limited number of ova, and females may bias the fertilization of their ova by particular sperm. Over evolutionary timescales, these two forms of selection shape both male and female reproductive physiology when females mate multiply, yet in monogamous systems, post-copulatory sexual selection is weak or absent. Here, we examine how divergent mating strategies within a genus of closely related mice, Peromyscus, have shaped the evolution of reproductive traits. We show that in promiscuous species, males exhibit traits associated with increased sperm production and sperm swimming performance, and females exhibit traits that are predicted to limit sperm access to their ova including increased oviduct length and a larger cumulus cell mass surrounding the ova, compared to monogamous species. Importantly, we found that across species, oviduct length and cumulus cell density are significantly correlated with sperm velocity, but not sperm count or relative testes size, suggesting that these female traits may have coevolved with increased sperm quality rather than quantity. Taken together, our results highlight how male and female traits evolve in concert and respond to changes in the level of post-copulatory sexual selection.  相似文献   

7.
Guppies (Poecilia reticulata) are models for understanding the interplay between natural and sexual selection. In particular, predation has been implicated as a major force affecting female sexual preferences, male mating tactics and the level of sperm competition. When predation is high, females typically reduce their preferences for showy males and engage more in antipredator behaviours, whereas males exploit these changes by switching from sexual displays to forced matings. These patterns are thought to account for the relatively high levels of multiple paternity in high‐predation populations compared to low‐predation populations. Here, we assess the possible evolutionary consequences of these patterns by asking whether variation in sperm traits reflect differences in predation intensity among four pairs of Trinidadian populations: four that experience relatively low levels of predation from a gape‐limited predator and four that experience relatively high levels of predation from a variety of piscivores. We found that males in high‐predation populations had faster swimming sperm with longer midpieces compared to males in low‐predation populations. However, we found no differences among males in high‐ and low‐predation populations with respect to sperm number, sperm head length, flagellum length and total sperm length.  相似文献   

8.
    
Some recent models suggest a new role for evolutionary arms races between males and females in sexual selection. Female resistance to males is proposed to be driven by the direct advantage to the female of avoiding male-imposed reductions in the number of offspring she can produce, rather than by the indirect advantage of selecting among possible sires for her offspring, as in some traditional models of sexual selection by female choice. This article uses the massive but hitherto under-utilized taxonomic literature on genitalic evolution to test, in a two-step process, whether such new models of arms races between males and females have been responsible for rapid divergent evolution of male genitalia. The test revolves around the prediction that 'new arms races' are less likely to occur in species in which females are largely or completely protected from unwanted sexual attentions from males (e.g. species which mate in leks or in male swarms, in which males attract females from a distance, or in which females initiate contact by attracting males from a distance). The multiple possible mechanical functions of male genitalia are summarized, and functions of male genitalic structures in 43 species in 21 families of Diptera are compiled. Functions associated with intromission and insemination (e.g. seizing and positioning the female appropriately, pushing past possible barriers within the female, orienting within the female to achieve sperm transfer), which are unlikely to be involved in new arms races when females are protected, are shown to be common (> 50 % of documented cases). This information is then used to generate the new arms race prediction: differences in genitalic form among congeneric species in which females are protected should be less common than differences among congeneric species in which females are vulnerable to harassment by males. This prediction was tested using a sample of 361 genera of insects and spiders. The prediction clearly failed, even when the data were adjusted to take into account several possible biases. Comparative analyses within particular taxonomic groups also failed to show the predicted trends, as did less extensive data on other non-genitalic male display traits. Arms races, as defined in some recent models, seem to have been less important in male-female coevolution of genitalic structures than has been suggested. By elimination, alternative interpretations, such as traditional female choice, which do not predict associations between female protection from harassment and rapid divergent evolution, are strengthened.  相似文献   

9.
  总被引：1，自引：0，他引：1  
Males of Microsepsis eberhardi and M. armillata use their genitalic surstyli to rhythmically squeeze the female's abdomen with stereotyped movements during copulation. Squeezing movements did not begin until intromission had occurred and, contrary to predictions of the conflict-of-interest hypothesis for genitalic evolution, did not overcome morphological or behavioral female resistance. Contrary to predictions of the lock-and-key hypothesis, female morphology was uniform in the two species and could not mechanically exclude the genitalia of either species of male. The complex pattern of squeezing movements differed between the two species as predicted by the sexual selection hypothesis for genitalic evolution. Also, evolutionarily derived muscles and pseudoarticulations in the male's genitalic surstyli facilitated one type of movement, whose patterns were especially distinct. The data support the hypothesis that the male surstyli evolved to function as courtship devices.  相似文献   

10.
Multiple mating by females is widely thought to encourage post-mating sexual selection and enhance female fitness. We show that whether polyandrous mating has these effects depends on two conditions. Condition 1 is the pattern of sperm utilization by females; specifically, whether, among females, male mating number, m (i.e. the number of times a male mates with one or more females) covaries with male offspring number, o. Polyandrous mating enhances sexual selection only when males who are successful at multiple mating also sire most or all of each of their mates'' offspring, i.e. only when Cov♂(m,o), is positive. Condition 2 is the pattern of female reproductive life-history; specifically, whether female mating number, m, covaries with female offspring number, o. Only semelparity does not erode sexual selection, whereas iteroparity (i.e. when Cov♀(m,o), is positive) always increases the variance in offspring numbers among females, which always decreases the intensity of sexual selection on males. To document the covariance between mating number and offspring number for each sex, it is necessary to assign progeny to all parents, as well as identify mating and non-mating individuals. To document significant fitness gains by females through iteroparity, it is necessary to determine the relative magnitudes of male as well as female contributions to the total variance in relative fitness. We show how such data can be collected, how often they are collected, and we explain the circumstances in which selection favouring multiple mating by females can be strong or weak.  相似文献   

11.
    
In many species, the negative fitness effects of inbreeding have facilitated the evolution of a wide range of inbreeding avoidance mechanisms. Although avoidance mechanisms operating prior to mating are well documented, evidence for postcopulatory mechanisms of inbreeding avoidance remain scarce. Here, we examine the potential for paternity biases to favour unrelated males when their sperm compete for fertilizations though postcopulatory inbreeding avoidance mechanisms in the guppy, Poecilia reticulata. To test this possibility, we used a series of artificial inseminations to deliver an equal number of sperm from a related (either full sibling or half sibling) and unrelated male to a female while statistically controlling for differences in sperm quality between rival ejaculates. In this way, we were able to focus exclusively on postcopulatory mechanisms of inbreeding avoidance and account for differences in sperm competitiveness between rival males. Under these carefully controlled conditions, we report a significant bias in paternity towards unrelated males, although this effect was only apparent when the related male was a full sibling. We also show that sperm competition generally favours males with highly viable sperm and thus that some variance in sperm competitiveness can be attributed to difference in sperm quality. Our findings for postcopulatory inbreeding avoidance are consistent with prior work on guppies, revealing that sperm competition success declines linearly with the level of relatedness, but also that such effects are only apparent at relatedness levels of full siblings or higher. These findings reveal that postcopulatory processes alone can facilitate inbreeding avoidance.  相似文献   

12.
    
In species where females store sperm, males may try to influence paternity by the strategic placement of sperm within the female's sperm storage organ. Sperm may be mixed or layered in storage organs, and this can influence sperm use beyond a ‘fair raffle’. In some insects, sperm from different matings is packaged into discrete packets (spermatodoses), which retain their integrity in the female's sperm storage organ (spermatheca), but little is known about how these may influence patterns of sperm use under natural mating conditions in wild populations. We examined the effect of the size and position of spermatodoses within the spermatheca and number of competing ejaculates on sperm use in female dark bushcrickets (Pholidoptera griseoaptera) that had mated under unmanipulated field conditions. Females were collected near the end of the mating season, and seven hypervariable microsatellite loci were used to assign paternity of eggs laid in the laboratory. Females contained a median of three spermatodoses (range 1–6), and only six of the 36 females contained more than one spermatodose of the same genotype. Both the size and relative placement of the spermatodoses within the spermatheca had a significant effect on paternity, with a bias against smaller spermatodoses and those further from the single entrance/exit of the spermatheca. A higher number of competing males reduced the chances of siring offspring for each male. Hence, both spermatodose size and relative placement in the spermatheca influence paternity success.  相似文献   

13.
Odonates were the first group of organisms where sperm competition and last male sperm precedence have been identified. With the development of 10 microsatellites for the emperor dragonfly Anax imperator, the function and priority patterns of the multiple sperm storage organs of females can be studied and compared between species in natural populations. In addition, two microsatellite loci developed for the sister species Anax parthenope, are also highly polymorphic in A. imperator. For the presented 12 microsatellite loci, the number of alleles per locus ranged from two to 24. Observed heterozygosity ranged from 0.07 to 0.88.  相似文献   

14.
    
In sedentary externally fertilizing species, direct interactions between mating partners are limited and prefertilization communication between sexes occurs largely at the gamete level. Certain combinations of eggs and sperm often have higher fertilization success than others, which may be contingent on egg‐derived chemical factors that preferentially attract sperm from compatible males. Here, we examine the mechanisms underlying such effects in the marine mussel Mytilus galloprovincialis, where differential sperm attraction has recently been shown to be associated with variation in offspring viability. Specifically, we focus on the sperm surface glycans, an individually unique layer of carbohydrates that moderate self‐recognition and other cellular‐level interactions. In many species egg‐derived factors trigger remarkable changes in the sperm's glycan layer, physiology, and swimming behavior, and thus potentially moderate mate choice at the gamete level. Here, we show that sperm glycan modifications and the strength of acrosome reaction are both dependent on specific male–female interactions (male–female combination). We also find associations between female‐induced sperm glycan changes and the Ca2+ influx into sperm–‐a key regulator of fertilization processes from sperm capacitation to gamete fusion. Together, our results suggest that female‐induced remote regulation of sperm physiology may constitute a novel mechanism of gamete‐level mate choice.  相似文献   

15.
    
It is now widely recognized that sexual selection has been important in the rapid and divergent evolution of male genital morphology. However, distinguishing among putative mechanisms of sexual selection acting on male genital morphology represents a considerable challenge. Although there is growing evidence that variation in the size and/or shape of male genital structures can determine a male's success in gaining fertilizations, our knowledge of the functional morphology of male genitalia remains limited. Here we examine the functional morphology of genital sclerites that are known to influence paternity in the dung beetle Onthophagus taurus . We show that three of the sclerites form a functionally integrated unit that generates the tubular-shaped spermatophore and delivers its opening to the female's spermathecal duct. A fourth sclerite acts as a holdfast device during copulation. Our observations shed light on the mechanism by which these sclerites influence a male's paternity, and their patterns of phenotypic and genetic (co)variation.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 257–266.  相似文献   

16.
    
Promiscuous mating systems provide the opportunity for females to bias fertilization toward particular males. However, distinguishing between male sperm competition and active female sperm choice is difficult for species with internal fertilization. Nevertheless, species that store and use sperm of different males in different storing structures and species where females are able to expel all or part of the ejaculates after copulation may be able to bias fertilization. We report a series of experiments aimed at providing evidence of female sperm choice in Euxesta eluta (Hendel), a species of ulidiid fly that expels and consumes ejaculates after copulation. We found no evidence of greater reproductive success for females mated singly, multiply with the same male, or mated multiply with different males. Female E. eluta possesses two spherical spermathecae and a bursa copulatrix for sperm storage, with a ventral receptacle. There was no significant difference in storing more sperm in spermathecae 24 h after copulation than immediately after copulation. Females mated with protein-fed males had greater reproductive success than similar females mated to protein-deprived males. Protein-fed females prevented to consume the ejaculate, retained more sperm when mated to protein-fed males than when mated to protein-deprived males. Our results suggest that female E. eluta can exert control of sperm retention of higher quality males through ejaculate ejection.  相似文献   

17.
  总被引：5，自引：1，他引：4  
  相似文献   

18.
The evolutionary significance of widespread hypo‐allometric scaling of genital traits in combination with rapid interspecific genital trait divergence has been of key interest to evolutionary biologists for many years and remains poorly understood. Here, we provide a detailed assessment of quantitative genital trait variation in males and females of the sexually highly dimorphic and cannibalistic orb‐weaving spider Argiope aurantia. We then test how this trait variation relates to sperm transfer success. In particular, we test specific predictions of the one‐size‐fits‐all and lock‐and‐key hypotheses for the evolution of genital characters. We use video‐taped staged matings in a controlled environment with subsequent morphological microdissections and sperm count analyses. We find little support for the prediction of the one‐size‐fits‐all hypothesis for the evolution of hypo‐allometric scaling of genital traits, namely that intermediate trait dimensions confer highest sperm transfer success. Likewise, our findings do not support the prediction of the lock‐and‐key hypothesis that a tight fit of male and female genital traits mediates highest sperm transfer success. We do, however, detect directional effects of a number of male and female genital characters on sperm transfer, suggesting that genital trait dimensions are commonly under selection in nature. Importantly, even though females are much larger than males, spermatheca size limits the number of sperm transferred, contradicting a previous hypothesis about the evolutionary consequences of genital size dimorphism in extremely size‐dimorphic taxa. We also find strong positive effects of male body size and copulation duration on the probability of sperm transfer and the number of sperm transferred, with implications for the evolution of extreme sexual size dimorphism and sexual cannibalism in orb weavers.  相似文献   

19.
Sex allocation theory predicts the optimal allocation to male and female reproduction in sexual organisms. In animals, most work on sex allocation has focused on species with separate sexes and our understanding of simultaneous hermaphrodites is patchier. Recent theory predicts that sex allocation in simultaneous hermaphrodites should strongly be affected by post-copulatory sexual selection, while the role of pre-copulatory sexual selection is much less clear. Here, we review sex allocation and sexual selection theory for simultaneous hermaphrodites, and identify several strong and potentially unwarranted assumptions. We then present a model that treats allocation to sexually selected traits as components of sex allocation and explore patterns of allocation when some of these assumptions are relaxed. For example, when investment into a male sexually selected trait leads to skews in sperm competition, causing local sperm competition, this is expected to lead to a reduced allocation to sperm production. We conclude that understanding the evolution of sex allocation in simultaneous hermaphrodites requires detailed knowledge of the different sexual selection processes and their relative importance. However, little is currently known quantitatively about sexual selection in simultaneous hermaphrodites, about what the underlying traits are, and about what drives and constrains their evolution. Future work should therefore aim at quantifying sexual selection and identifying the underlying traits along the pre- to post-copulatory axis.  相似文献   

20.
Sperm morphometry is extremely variable across species, but a general adaptive explanation for this diversity is lacking. As sperm must function within the female, variation in sperm form may be associated with variation in female reproductive tract morphology. We investigated this and other potential evolutionary associations between male and female reproductive characters across the Scathophagidae. Sperm length was positively associated with the length of the spermathecal (sperm store) ducts, indicating correlated evolution between the two. No association was found between sperm length and spermathecal size. However, the size of the spermathecae was positively associated with testis size indicating co-evolution between male investment in sperm production and female sperm storage capacity. Furthermore, species with a higher degree of polyandry (larger testes) had longer spermathecal ducts. However, no associations between sperm length or length variation and testis size were found which suggests greater sperm competition sensu stricto does not select for longer sperm.  相似文献   

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