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1.
Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within‐species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male–male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.  相似文献   

2.
Detailed studies of reproductive isolation and how it varies among populations can provide valuable insight into the mechanisms of speciation. Here we investigate how the strength of premating isolation varies between sympatric and allopatric populations of threespine sticklebacks to test a prediction of the hypothesis of reinforcement: that interspecific mate discrimination should be stronger in sympatry than in allopatry. In conducting such tests, it is important to control for ecological character displacement between sympatric species because ecological character divergence may strengthen prezygotic isolation as a by-product. We control for ecological character displacement by comparing mate preferences of females from a sympatric population (benthics) with mate preferences of females from two allopatric populations that most closely resemble the sympatric benthic females in ecology and morphology. No-choice mating trials indicate that sympatric benthic females mate less readily with heterospecific (limnetic) than conspecific (benthic) males, whereas two different populations of allopatric females resembling benthics show no such discrimination. These differences demonstrate reproductive character displacement of benthic female mate choice. Previous studies have established that hybridization between sympatric species occurred in the past in the wild and that hybrid offspring have lower fitness than either parental species, thus providing conditions under which natural selection would favor individuals that do not hybridize. Results are therefore consistent with the hypothesis that female mate preferences have evolved as a response to reduced hybrid fitness (reinforcement), although direct effects of sympatry or a biased extinction process could also produce the pattern. Males of the other sympatric species (limnetics) showed a preference for smaller females, in contrast to the inferred ancestral preference for larger females, suggesting reproductive character displacement of limnetic male mate preferences as well.  相似文献   

3.
Abstract Barriers to gene flow that act after mating but before fertilization are often overlooked in studies of reproductive isolation. Where species are sympatric, such "cryptic' isolating barriers may be important in maintaining species as distinct entities. Drosophilayakuba and its sister species D. santomea have overlapping ranges on the island of Sao Tome, off the coast of West Africa. Previous studies have shown that the two species are strongly sexually isolated. However, the degree of sexual isolation observed in the laboratory cannot explain the low frequency (–1%) of hybrids observed in nature. This study identifies two "cryptic" isolating barriers that may further reduce gene flow between D. yakuba andD. santomea where they are sympatric. First, noncompetitive gametic isolation has evolved between D. yakuba and D. santomea: heterospecific matings between the two species produce significantly fewer offspring than do conspecific matings. Second, conspecific sperm precedence (CSP) occurs when D. yakuba females mate with conspecific and heterospecific males. However, CSP is asymmetrical: D. santomea females do not show patterns of sperm usage consistent with CSP. Drosophila yakuba and D. santomea females also differ with respect to remating propensity after first mating with conspecific males. These results suggest that noncompetitive and competitive gametic isolating barriers may contribute to reproductive isolation between D. yakuba and D. santomea.  相似文献   

4.
Abstract Many studies of speciation rely critically on estimates of sexual isolation obtained in the laboratory. Here we examine the sensitivity of sexual isolation to alterations in experimental design and mating environment in two sister species of Drosophila, D. santomea and D. yakuba. We use a newly devised measure of mating frequencies that is able to disentangle sexual isolation from species differences in mating propensity. Variation in fly density, presence or absence of a quasi‐natural environment, degree of starvation, and relative frequency of species had little or no effect on sexual isolation, but one factor did have a significant effect: the possibility of choice. Designs that allowed flies to choose between conspecific and heterospecific mates showed significantly more sexual isolation than other designs that did not allow choice. These experiments suggest that sexual isolation between these species (whose ranges overlap on the island of STo Tomé) is due largely to discrimination against D. yakuba males by D. santomea females. This suggestion was confirmed by direct observations of mating behavior. Drosophila santomea males also court D. yakuba females less ardently than conspecific females, whereas neither males nor females of D. yakuba show strong mate discrimination. Thus, sexual isolation appears to be a result of evolutionary changes in the derived island endemic D. santomea. Surprisingly, as reported in a companion paper (Llopart et al. 2005), the genotypes of hybrids found in nature do not accord with expectations from these laboratory studies: all F1 hybrids in nature come from matings between D. santomea females and D. yakuba males, matings that occur only rarely in the laboratory.  相似文献   

5.
Reproductive isolation restricts genetic exchange between species. Various pre- and post-mating barriers, such as behavior, physiology and gametic incompatibility, have been shown to evolve in sympatry. In certain scenarios, isolation can be asymmetrical, where species differentially prefer conspecifics. We examined sexual isolation via conspecific mate preference between Gambusia affinis and G. geiseri in both sexes. To investigate male contribution to sexual isolation, we compared the number of mating attempts (gonopodial thrusts) directed at either a conspecific or a heterospecific female, in both species. We also examined sperm priming and expenditure in males in the presence of conspecific or heterospecific females. We then measured female preference for either a conspecific or heterospecific male, in both species. We found that males of both species preferred to mate with conspecific females, but showed no difference in sperm production or expenditure between conspecific and heterospecific females. Females of both species did not prefer conspecific over heterospecific males. Our results suggest that sexual isolation might be mediated by male mate choice in this system and not female choice, suggesting that there is asymmetrical reproductive isolation between the sexes in G. affinis and G. geiseri, but symmetrical species isolation.  相似文献   

6.
One-allele isolating mechanisms should make the evolution of reproductive isolation between potentially hybridizing taxa easier than two-allele mechanisms, but the generality of one-allele mechanisms in nature has yet to be established. A potentially important one-allele mechanism is sexual imprinting, where the mate preferences of individuals are based on the phenotype of their parents. Here I test the possibility that sexual imprinting promotes reproductive isolation using sympatric species of threespine sticklebacks (Gasterosteus aculeatus). Sympatric species of sticklebacks consist of large benthic species and small limnetic species that are reproductively isolated and adapted to feeding in different environments. I fostered families of F1 hybrids between the species to males of both species. Preferences of these fostered females for males of either type revealed little or no effect of sexual imprinting on assortative mating. However, F1 females showed preferences for males that were similar to themselves in length, suggesting that size-assortative mating may be more important than sexual imprinting for promoting reproductive isolation between species pairs of threespine sticklebacks.  相似文献   

7.
SUMMARY. 1. We examined the seasonal distributions and mating behaviour of Epischura lacustris, Diaptomus minutus and Diaptomus oregonensis to evaluate several proposed mechanisms for reproductive isolation. There was no divergence in onset of maturity or timing of breeding periods between sympatric diaptomid populations; size displacement between co-occurring diaptomid species did not result in concomitant reduction in mating frequency between heterospecific pairs in the laboratory.
2. Divergence in mating behaviour was supported by observations that, in conspecific mating experiments, males of both diaptomid species discriminated between females bearing ripened ovaries (gravid) and those that did not (non-gravid), and that, in heterospecific trials, males either mated indiscriminantly with all females, or engaged in mating very infrequently.
3. In mating experiments with Epischura. males did not discriminate between gravid and non-gravid females, but mated exclusively with virgins of a specific relative size. Divergence in timing of breeding seasons between Epischura and the two diaptomid species suggests that even if mating between genera is possible, it does not occur often in nature.
4. We discuss the adaptive significance of different reproductive strategies of these three copepods and speculate on mechanisms that allow for coexistence of the closely related taxa in nature.  相似文献   

8.
Aedes (Stegomyia) albopictus and Aedes (Stegomyia) flavopictus are related species that have overlapping distributions from southern to central Japan. To understand how they interact, we studied reproductive interference between them, particularly focusing on the body size difference between the mating pair. Here, we examined the effects of conspecific, heterospecific and double mating (i.e. heterospecific mating followed by conspecific mating) on copulation duration, egg production and hatchability of eggs using mosquitoes that varied in body size. Females mated only with heterospecific males produced few viable eggs, indicating that post‐mating isolation is almost complete. When mated with heterospecific males before conspecific mating, the production of viable eggs was lower than when mated only with conspecific males, revealing the occurrence of reproductive interference. The degree of reproductive interference was larger in Ae. flavopictus than in Ae. albopictus when the female size was small but did not differ between them when the female size was large. Aedes albopictus females appear to be able to distinguish Ae. flavopictus males from conspecific males and larger females are more successful in the rejection of heterospecific males. On the other hand, Ae. flavopictus were not able to discriminate between conspecific and heterospecific males.  相似文献   

9.
Understanding speciation hinges on understanding how reproductive barriers arise between incompletely isolated populations. Despite their crucial role in speciation, prezygotic barriers are relatively poorly understood and hard to predict. We use two closely related cricket species, Gryllus bimaculatus and G. campestris, to experimentally investigate premating barriers during three sequential mate choice steps. Furthermore, we experimentally show a significant difference in polyandry levels between the two species and subsequently test the hypothesis that females of the more polyandrous species, G. bimaculatus, will be less discriminating against heterospecific males and hence hybridise more readily. During close-range mating behaviour experiments, males showed relatively weak species discrimination but females discriminated very strongly. In line with our predictions, this discrimination is asymmetric, with the more polyandrous G. bimaculatus mating heterospecifically and G. campestris females never mating heterospecifically. Our study shows clear differences in the strength of reproductive isolation during the mate choice process depending on sex and species, which may have important consequences for the evolution of reproductive barriers.  相似文献   

10.
Species coexistence involves the evolution of reproductive barriers opposing gene flow. Heliconius butterflies display colorful patterns affecting mate choice and survival through warning signaling and mimicry. These patterns are called “magic traits” for speciation because divergent natural selection may promote mimicry shifts in pattern whose role as mating cue facilitates reproductive isolation. By contrast, between comimetic species, natural selection promotes pattern convergence. We addressed whether visual convergence interferes with reproductive isolation by testing for sexual isolation between two closely related species with similar patterns, H. timareta thelxinoe and H. melpomene amaryllis. Experiments with models confirmed visual attraction based on wing phenotype, leading to indiscriminate approach. Nevertheless, mate choice experiments showed assortative mating. Monitoring male behavior toward live females revealed asymmetry in male preference, H. melpomene males courting both species equally while H. timareta males strongly preferred conspecifics. Experiments with hybrid males suggested an important genetic component for such asymmetry. Behavioral observations support a key role for short‐distance cues in determining male choice in H. timareta. Scents extracts from wings and genitalia revealed interspecific divergence in chemical signatures, and hybrid female scent composition was significantly associated with courtship intensity by H. timareta males, providing candidate chemical mating cues involved in sexual isolation.  相似文献   

11.
Female mate preferences for ecologically relevant traits may enhance natural selection, leading to rapid divergence. They may also forge a link between mate choice within species and sexual isolation between species. Here, we examine female mate preference for two ecologically important traits: body size and body shape. We measured female preferences within and between species of benthic, limnetic, and anadromous threespine sticklebacks (Gasterosteus aculeatus species complex). We found that mate preferences differed between species and between contexts (i.e., within vs. between species). Within species, anadromous females preferred males that were deep bodied for their size, benthic females preferred larger males (as measured by centroid size), and limnetic females preferred males that were more limnetic shaped. In heterospecific mating trials between benthics and limnetics, limnetic females continued to prefer males that were more limnetic like in shape when presented with benthic males. Benthic females showed no preferences for size when presented with limnetic males. These results show that females use ecologically relevant traits to select mates in all three species and that female preference has diverged between species. These results suggest that sexual selection may act in concert with natural selection on stickleback size and shape. Further, our results suggest that female preferences may track adaptation to local environments and contribute to sexual isolation between benthic and limnetic sticklebacks.  相似文献   

12.
In this study we assessed whether sexual selection against hybrids contributes to reproductive isolation between two sympatric stickleback species. The species are recently diverged and possibly in the final stages of speciation. Our aim was to find whether mating discrimination of the parental species selects against F1 hybrids, and what conditions are necessary for such sexual selection to operate. We used conservative no-choice laboratory trials with reproductively naive, lab-reared fish to measure female mating preferences. Females exhibited ranked preferences, preferring in order: conspecific, hybrid, then heterospecific males. However, intermediate attractiveness does not necessarily imply selection against hybrids: two-way ANOVAs suggested that limnetic, benthic, and hybrid males were statistically equivalent when averaged across females. Thus, this experiment found no evidence for a hybrid mating disadvantage. Our interpretation is that if sexual selection against hybrids is present in the wild, then some factor that biases encounter rates between hybrids and parental species (e.g., habitat selection) is necessary to produce it.  相似文献   

13.
Reinforcement occurs when hybridization between closely related lineages produces low‐fitness offspring, prompting selection for elevated reproductive isolation specifically in areas of sympatry. Both premating and postmating prezygotic behaviors have been shown to be the target of reinforcing selection, but it remains unclear whether remating behaviors experience reinforcement, although they can also influence offspring identity and limit formation of hybrids. Here, we evaluated evidence for reinforcing selection on remating behaviors in Drosophila pseudoobscura, by comparing remating traits in females from populations historically allopatric and sympatric with Drosophila persimilis. We found that the propensity to remate was not higher in sympatric females, compared to allopatric females, regardless of whether the first mated male was heterospecific or conspecific. Moreover, remating behavior did not contribute to interspecific reproductive isolation among any population; that is, females showed no higher propensity to remate following a heterospecific first mating than following a conspecific first mating. Instead, we found that females are less likely to remate after initial matings with unfamiliar males, regardless of species identity. This is consistent with one scenario of postmating sexual conflict in which females are poorly defended against postcopulatory manipulation by males with whom they have not coevolved. Our results are generally inconsistent with reinforcement on remating traits and suggest that this behavior might be more strongly shaped by the consequences of local antagonistic male–female interactions than interactions with heterospecifics.  相似文献   

14.
In this study, female preferences and behavioural isolation were estimated in a pair of allopatric sister species, Etheostoma duryi and Etheostoma flavum. Dichotomous mate preference trials were conducted to determine whether females prefer to associate with conspecific over heterospecific males and free‐spawning assays were conducted to determine whether those preferences translated into behavioural isolation. Dichotomous mate choice trials revealed asymmetric female preference, as female E. flavum preferred conspecific males, whereas female E. duryi showed no preference. Free‐spawning assays indicated that behavioural isolation remains incomplete between E. duryi and E. flavum (IB = 0·19). In addition to female mating preferences, male behaviour also appeared to influence mating outcomes as male E. flavum consistently courted conspecific females more often in free‐spawning assays whereas male E. duryi did not. The data therefore suggest that despite marked divergence in male nuptial colour, divergence in female preferences between these species may not be sufficient to maintain species boundaries upon secondary contact. These results contrast with similar work in a sympatric darter species pair and may be explained by considering the contributions of reinforcement and differences in colour pattern as well as colour value.  相似文献   

15.
The reproductive success of the sneaky mating tactic is difficult to determine in fish with internal fertilization. We approached this problem by developing an assay that allows the recovery of sperm DNA from the reproductive tract of females. This assay was used to test whether sperm transfer occurs between sympatric populations of the guppy, Poecilia reticulata , and its putative sister species, Poecilia picta . Six hundred females of both species from two sympatric sites in Trinidad were collected, and then the contents of the females' reproductive tracts were analysed using reciprocally diagnostic microsatellite markers. Conspecific sperm occurred in approximately 86% of females, whereas heterospecific sperm were found in only 4% of females. Because females of either species do not mate willingly with heterospecific males, the results indicate that sneaky mating results in the transfer of sperm. The data are consistent with the idea that sexual conflict can result in differences in the strength of behavioural isolation between the sexes, and they suggest that behavioural isolation is unlikely to have driven speciation between the guppy and P. picta .  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 397–402.  相似文献   

16.
Sexual isolation is often assumed to arise because choosy females recognize and reject heterospecific males as mates. Yet in taxa in which both males and females are choosy, males might also recognize and reject heterospecific females. Here, we asked about the relative contribution of the sexes to the strong sexual isolation found in limnetic–benthic species pairs of threespine sticklebacks, which show mutual mate choice. We asked whether males and females of the two species recognize conspecifics and also prefer to mate with them. We found evidence for mate recognition by both sexes but only females prefer conspecifics. The nature of male courtship depended on which species of female they were courting, indicating that males recognized conspecific females and differentiated them from heterospecifics. However, males courted both species of females with equal vigor and changed courtship in a manner that would increase the chance of mating with heterospecifics. Females both recognized conspecifics and strongly preferred them. They responded very little to heterospecific male courtship and almost never mated with them. Therefore, males are likely to undermine sexual isolation, but females uphold it. Despite mutual mate choice and mate recognition in both sexes, females are primarily responsible for sexual isolation in these taxa.  相似文献   

17.
External male reproductive structures have received considerable attention as a cause of reproductive isolation (RI), because the morphology of these structures often evolves rapidly between populations. This rapid evolution presents the potential for mechanical incompatibilities with heterospecific female structures during mating and could thus prevent interbreeding between nascent species. Although such mechanical incompatibilities have received little empirical support as a common cause of RI, the potential for mismatch of reproductive structures to cause RI due to incompatible species‐specific tactile cues has not been tested. We tested the importance of mechanical and tactile incompatibilities in RI between Enallagma anna and E. carunculatum, two damselfly species that diverged within the past ~250,000 years and currently hybridize in a sympatric region. We quantified 19 prezygotic and postzygotic RI barriers using both naturally occurring and laboratory‐reared damselflies. We found incomplete mechanical isolation between the two pure species and between hybrid males and pure species females. Interestingly, in mating pairs for which mechanical isolation was incomplete, females showed greater resistance and refusal to mate with hybrid or heterospecific males compared to conspecific males. This observation suggests that tactile incompatibilities involving male reproductive structures can influence female mating decisions and form a strong barrier to gene flow in early stages of speciation.  相似文献   

18.
Shaw KL  Lugo E 《Molecular ecology》2001,10(3):751-759
Based on studies from native Hawaiian Drosophila, a model was proposed to explain sexual isolation and mating asymmetry, from which one could potentially infer the 'direction of evolution'. We examined sexual isolation between allopatric cricket species of the genus Laupala, another endemic Hawaiian insect with an elaborate mating system, to begin to explore the nature of sexual isolation and mating asymmetry in closely related Hawaiian organisms. We studied sexual isolation and mating asymmetry in two contrasts. First, an inter-island comparison, including L. makaio from the older island of Maui and L. paranigra from the younger island of Hawaii, and second, an intra-island (Hawaii) comparison, including L. nigra from the older volcano of Mauna Kea and L. paranigra with a primary distribution on the younger volcanoes of Mauna Loa and Kilauea. We used a 'no-choice' experimental design, pairing individual males and females in homospecific or heterospecific combinations. Several behavioural aspects of courtship (proportion of male singing, latency to male singing, production of spermatophores and courtship initiation speed) were quantified as well as the success or failure of matings. We demonstrate asymmetry in sexual isolation between reciprocal combinations of L. makaio and L. paranigra. This result is examined in light of the differences in courtship behaviour manifest in the experiments with these two species. We did not find evidence of asymmetry in sexual isolation between L. nigra and L. paranigra, although differences in courtship initiation speed were evident between reciprocal combinations of these two species. In addition to the geological argument that species on older islands and older volcanoes give rise to species on younger islands and younger volcanoes, we discuss phylogenetic evidence consistent with these biogeographic hypotheses of relationships among the focal taxa. The patterns of asymmetrical sexual isolation and mating asymmetry are consistent with those found in the native Hawaiian Drosophila.  相似文献   

19.
Predation risk can alter female mating decisions because the costs of mate searching and selecting attractive mates increase when predators are present. In response to predators, females have been found to plastically adjust mate preference within species, but little is known about how predators alter sexual isolation and hybridization among species. We tested the effects of predator exposure on sexual isolation between benthic and limnetic threespine sticklebacks (Gasterosteus spp.). Female discrimination against heterospecific mates was measured before and after females experienced a simulated attack by a trout predator or a control exposure to a harmless object. In the absence of predators, females showed increased aversion to heterospecifics over time. We found that predator exposure made females less discriminating and precluded this learned aversion to heterospecifics. Benthic and limnetic males differ in coloration, and predator exposure also affected sexual isolation by weakening female preferences for colourful males. Predator effects on sexual selection were also tested but predators had few effects on female choosiness among conspecific mates. Our results suggest that predation risk may disrupt the cognitive processes associated with mate choice and lead to fluctuations in the strength of sexual isolation between species.  相似文献   

20.
Data on patterns of variation within hybrid zones, combined with studies of life history, mate choice, and hybrid performance, allow estimates of the contribution of different pre-zygotic and post-zygotic barriers to reproductive isolation. We examine the role of behavioural barriers to gene exchange in the maintenance of a hybrid zone between North American field crickets Gryllus firmus and Gryllus pennsylvanicus . We consider these barriers in the context of previous studies that documented temporal and ecological isolation and a one-way post-mating incompatibility (i.e. G. firmus females do not produce offspring when they mate only with heterospecific males). Based on no-choice mating experiments in the laboratory, we demonstrate strong behavioural pre-mating barriers between the two species, but no apparent fecundity or fertility costs for G. firmus females when they mate with both conspecific and heterospecific males. Furthermore, we show that G. firmus females do not discriminate between hybrids and conspecifics, whereas G. pennsylvanicus females do. This observation could explain the asymmetric allele introgression observed in the hybrid zone. We also document a failure of heterospecific males to induce normal oviposition in G. firmus females, which may be due to rapid evolution of accessory gland proteins and may serve as an additional barrier to gene exchange.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 390–402.  相似文献   

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