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(a) Principle component analysis of allele frequency variation for all loci in 12 populations of Poecilia latipinna. Open circles are sympatric populations, filled circles, are allopatric populations. (b) Results of multidimensional scaling analyses, displayed as pairwise two dimensional scatterplots using dimension one vs dimension two. (c) MDS of dimension one vs. dimension three. The first two dimensions account for most of the differentiation and the first three dimensions account for virtually all of the differentiation. Population designations are the same as in Figure 1.
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We analyzed variation in allozymes and mating preferences in 12 populations across much of the range of the sailfin molly, Poecilia latipinna. Sailfin mollies can be sympatric with its sexual parasite Amazon mollies, P. formosa. Amazon mollies must co-exist and mate with bisexual males of closely related species (including sailfin mollies) to induc...
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Mathematical models have played an important role in the development of sexual selection theory. These models come in different flavors and they differ in their assumptions, often in a subtle way. Similar questions can be addressed by modeling frameworks from population genetics, quantitative genetics, evolutionary game theory, or adaptive dynamics...
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... Previous attempts to cross the parental species are not informative here, because they were set up as forced crosses of one or several unmated (virgin) female(s) and one or several males, leaving little opportunity for females to exercise mate choice. In general, mate choice in this system has been addressed widely (Schlupp, 2005(Schlupp, , 2009(Schlupp, , 2018, including character displacement in males (Gabor et al., 2005;Gabor & Ryan, 2001). Many hypotheses exist that can explain female preferences, including an almost universal preference for larger males size (Ryan & Keddy-Hector, 1992), but in the context of this study, the idea of a preexisting bias governing mate preferences of female mollies, in particular females of species with short dorsal fins (Ptacek, 1998) because males are more ornamented, seems particularly relevant (Endler & Basolo, 1998;Ryan, 1990) (Figure 1). ...
The role of hybridization as a formative process in evolution has received much attention in the past few decades. A particularly fascinating outcome of hybrid speciation is the formation of asexual hybrid species. The Amazon molly ( Poecilia formosa ) is such a hybrid and originated from a P. mexicana mother and a P. latipinna father. Consequently, a heterospecific mating must have occurred leading to the Amazon molly, indicating a breakdown of any potential prezygotic isolation between parental species. Here we studied the female mate preferences of extant P. mexicana and P. latipinna from several populations using standard binary choice tests with males of both sexual species that were matched for size. Poecilia mexicana and P. latipinna can be crossed in the lab, however, the offspring are not asexual, but sexual F 1 s. In our study, we generated F 1 s and tested their mating preferences with sexual males of both P. mexicana and P. latipinna against F 1 males. Overall, our results show that in extant P. mexicana and P. latipinna no female preference for conspecific males was detectable. Consequently, heterospecific matings are possible and not hindered by any apparent behavioral prezygotic isolation. If female preferences in these species were comparable around the time the Amazon molly originated as a hybrid species ca. 100,000 years ago, matings leading to hybrids would be very likely. F 1 females also have no discernable mating preferences for either sexual males or F 1 males. Such lack of prezygotic behavioral isolation could potentially lead to F 2 individuals, backcrosses, and introgression.
... While only a few studies examined geographical variation in male mate choice against asexuals, some empirical support for such hypothesis exists. For instance, Gabor and Ryan (2001) and Gabor et al. (2005) found that males of the sexual sailfin molly (P. latipinna) living sympatrically with gynogenetic Amazon mollies (P. ...
Sexual reproduction is the primary mode of reproduction in eukaryotes, but some organisms have evolved deviations from classical sex and switched to asexuality. These asexual lineages have sometimes been viewed as evolutionary dead ends, but recent research has revealed their importance in many areas of general biology. Our review explores the understudied, yet important mechanisms by which sperm‐dependent asexuals that produce non‐recombined gametes but rely on their fertilization, can have a significant impact on the evolution of coexisting sexual species and ecosystems. These impacts are concentrated around three major fields. Firstly, sperm‐dependent asexuals can potentially impact the gene pool of coexisting sexual species by either restricting their population sizes or by providing bridges for interspecific gene flow whose type and consequences substantially differ from gene flow mechanisms expected under sexual reproduction. Secondly, they may impact on sexuals' diversification rates either directly, by serving as stepping‐stones in speciation, or indirectly, by promoting the formation of pre‐ and postzygotic reproduction barriers among nascent species. Thirdly, they can potentially impact on spatial distribution of species, via direct or indirect (apparent) types of competition and Allee effects. For each such mechanism, we provide empirical examples of how natural sperm‐dependent asexuals impact the evolution of their sexual counterparts. In particular, we highlight that these broad effects may last beyond the tenure of the individual asexual lineages causing them, which challenges the traditional perception that asexual lineages are short‐lived evolutionary dead ends and minor sideshows. Our review also proposes new research directions to incorporate the aforementioned impacts of sperm‐dependent asexuals. These research directions will ultimately enhance our understanding of the evolution of genomes and biological interactions in general.
... Note: Total isolation represents the sum of all conspecific-and heterospecific-directed behaviors across all measured behaviors.Abbreviations: EF, East Fork Barren River; FC, French Creek tributaries; LC, Line Creek; MF, Middle Fork Red River. specific preference decreasing as distance from sympatry increases(Gabor, Ryan, & Morizot, 2005;Gregorio et al., 2012;Kronforst et al., 2007). There was no significant variation in SOP between allo-patric populations of E. zonale despite large geographical distances between the two allopatric sites. ...
Abstract Reinforcement occurs when selection against hybrid offspring strengthens behavioral isolation between parental species and may be an important factor in speciation. Theoretical models and experimental evidence indicate that both female and male preferences can be strengthened upon secondary contact via reinforcement. However, the question remains whether this process is more likely to affect the preferences of one sex or the other. Males of polygynous species are often predicted to exhibit weaker preferences than females, potentially limiting the ability for reinforcement to shape male preferences. Yet, in darters (Percidae: Etheostoma), male preference for conspecific mates appears to arise before female preferences during the early stages of allopatric speciation, and research suggests that male, but not female, preferences become reinforced upon secondary contact. In the current study, we aimed to determine whether the geographically widespread darter species Etheostoma zonale exhibits a signature of reinforcement, by comparing the strength of preference for conspecific mates between populations that are sympatric and allopatric with respect to a close congener, E. barrenense. We examined the strength of preference for conspecifics for males and females separately to determine whether the preferences of one or both sexes have been strengthened by reinforcement. Our results show that both sexes of E. zonale from sympatric populations exhibit stronger conspecific preferences than E. zonale from allopatric populations, but that female preferences appear to be more strongly reinforced than male preferences. Results therefore suggest that reinforcement of female preferences may promote behavioral isolation upon secondary contact, even in a genus that is characterized by pervasive male mate choice.
... Sailfin and Atlantic mollies not only show populations that occur in sympatry with Amazon mollies, but also populations that occur in allopatry. This creates an opportunity for work comparing characters, including male mate choice between allopatric and sympatric populations (Gabor & Ryan 2001, Gabor et al. 2005. ...
Although the majority of studies on mate choice focus on female mate choice, there is growing recognition of the role of male mate choice, too. Male mate choice is tightly linked to two other phenomena, female competition for males, and ornamentation in females. In the current paper I review the existing literature on this in a group of fishes, Poeciliidae. In this group male mate choice appears to be based on differences in female quality, especially female size, which is a proxy for fecundity. Some males also have to choose between heterospecific and conspecific females in the unusual mating system of the Amazon molly. In this case, they typically show a preference for conspecific females. While male mate choice is relatively well documented for this family, female ornamentation and female competition are not.
... L. Berdan, unpublished data). Our study adds to growing evidence that male Our data suggest a relationship between preference strength and proximity to heterospecific populations similar to previous studies in Heliconius butterflies and salifin mollies which have found that the strength of male conspecific preference is directly related to the distance from sympatric populations (Gabor et al. 2005;Kronforst et al. 2007). Therefore, reinforcement may frequently produce clinal effects on preference when gene flow occurs between sympatric and neighboring populations (Lemmon et al. 2004;Goldberg and Lande 2006). ...
Reinforcement occurs when reduced hybrid fitness
leads to the evolution of a stronger prezygotic isolation. Populations
sympatric with closely related species, where hybridization
occurs, are predicted to have stronger mate preferences
than allopatric populations. The reinforcement of male mate
preference is thought to be rarer than the reinforcement of
female preference, but this inference may be biased by the lack
of studies on male preference.We tested male mate preferences
from sympatric and allopatric populations of two closely related
species of killifish: Lucania goodei and Lucania parva. We
found that sympatric males had greater preferences for conspecific
females than allopatric males. Furthermore, conspecific
preferences in allopatric populations were weakest when these
populations were geographically distant (>50 km) from those
of heterospecifics. Our data suggest that reinforcement has
contributed to male conspecific preference and speciation in
Lucania.
... The differences among the mating and hormonal responses of sailfin and Atlantic mollies parallel intraspecific differences among populations of mollies and suggest rapid evolution of mating behaviors. Differentiation in male mating behavior among sailfin molly populations has occurred faster than differentiation at allozyme loci [49], possibly due to strong selective pressures from parasitic Amazon mollies over approximately 120,000 years [50,18,19]. Behavioral evolution has resulted in reproductive character displacement in mating preferences between sympatric and allopatric populations [25]. ...
Much is known about the role of hormones in the regulation of vertebrate mating behavior, including receptivity, and several components of mate choice. Hormones may modulate reproductive behavior in such a way to increase or decrease the individual's motivation, and therefore hormones may be important in mediating behavior associated with reproductive isolation. The mating complex of the all female gynogenetic Amazon mollies, Poecilia formosa, and their parental species (sailfin mollies, P. latipinna, and Atlantic mollies, P. mexicana) is a model system for studying ultimate mechanisms of species recognition. However, proximate mechanisms, such as variation in hormone levels, and the effect of hormones on sperm production have not been extensively examined. We predict that one or more of the sex steroid hormones in teleost fish (11-ketotestosterone (KT), testosterone (T), and estradiol (E)) will play a role in species recognition (during mate choice and/or sperm priming) for Atlantic mollies (the maternal parental species) that are sympatric with Amazon mollies. We sequentially paired male Atlantic mollies with female conspecifics and Amazon mollies and obtained water-borne hormone samples before and after mating for all fish. We measured circulating KT, T, and E from the water samples. Although we did not find an overall KT response to mating with conspecifics as has been found previously in sailfin mollies, male Atlantic mollies that mated more with conspecific females had lower postmating T levels. Additionally, males attempted to mate more with conspecific females that had lower postmating E levels, but attempted to mate more with Amazon mollies that had higher postmating KT levels. We also examined the effect of KT on sperm priming (a mechanism of premating mate choice), and found that KT levels of male Atlantic mollies prior to mating are correlated with the sperm priming response when males were paired with conspecific females, but this correlation was not found when males were paired with Amazon mollies. Our results indicate that male mating behavior is affecting or responding to both male and female hormones, but that the hormones alone are not playing a role in species recognition. Male Atlantic mollies may not discriminate against Amazon mollies as strongly as male sailfin mollies because Amazon mollies resemble their maternal parental species more than their paternal species.
... It was clear from the distribution of genetic variation and from estimates of recent migration that adaptation to the high sulfide environment restricted gene flow between this population and the other sites. Gabor et al. (2005) measured allozymic and behavioral variation across the range of one of the sailfin mollies, P. latipinna. They compared populations that were sympatric and allopatric with P. formosa, the amazon molly. ...
... In addition, there seems to be variation in male preferences over the mating season and based on geographic area . Most importantly, sexual males living allopatrically from Amazon mollies seem to have a stronger preference for conspecifics, indicating that at least males of P. latipinna have evolved character displacement in response to the presence of Amazon mollies (Gabor and Ryan, 2001;Gabor et al., 2005). ...
The livebearing all-female fish Poecilia formosa reproduces by gynogenesis, a modified form of parthenogenesis. P. formosa forms at least two breeding complexes: in its northern range it exists sympatrically with Poecilia latipinna and in its southern range with Poecilia mexicana. Differences between these complexes and their possible origin are discussed. Embryogenesis is triggered by sperm of males of these closely related sympatric species. Because inheritance is strictly maternal, from the male point of view energy and time invested are totally lost.
In this study we wanted to elucidate whether males are able to distinguish between conspecific and parasitic females. It could be shown that males are able to distinguish females optically, but that this ability was obscured as soon as chemical and/or tactile contact was possible.
Furthermore, we found that females in an attractive phase of their sexual cycle are always preferred, regardless of species. This is possibly the mechanism by which parasitic females obtain the matings they need to reproduce.
... The fact that females generally appear to be the choosiest sex in most animals may give rise to a bias in evolutionary research [9]. However some recent studies mentioned the occurrence of RCD in male mate preferences [10][11][12][13]. Occurrence of male mate choice in species from different taxa (actinopterygians, birds, insects, mammals) and contribution of female sexual traits and male choosiness to specific reproductive isolation [14,15] may indicate that this phenomenon is more common than previously thought. ...
... The local divergence of male mating calls of Hyla cinerea in ponds where H. gratiosa breeds syntopically [6] tends to support this idea. Additionally, cases have been reported where local adaptation in sexual behaviour persisted despite high gene flow [11,71]. ...
Patterns of gene flow at different spatial and taxonomic scales represent a key question in evolutionary biology. Analysis of gene flow between species or populations provides a better understanding of the development of intrinsic and environmental barriers which are responsible for divergence or differentiation between groups. We studied barriers to gene flow at the inter- and intraspecific levels in two amphibian species: the palmate newt Lissotriton helveticus and the smooth newt L. vulgaris. First, we studied introgression and maintenance of integrity in these two broadly sympatric species. Despite a low hybridization rate, most populations show introgression events. We highlighted a reproductive character displacement and showed that specific recognition is probably the most powerful reason for reproductive isolation. However, exogenous factors influencing sex-ratio, ratio of size or signal transmission for specific recognition may improve mismating and thus the likelihood of hybridization. Yet, the frequency of hybridization events probably does not compensate for the loss of heterospecific genes by genetic drift from one population to another. Secondly, at the intraspecific level, the study of polymorphism variation on the palmate newts in the Loire valley highlighted a low but significant structure at microsatellite locus. This metapopulation structure is shaped by some landscape features acting as barriers (rivers) or dispersal corridor (floodplain). Population structure and variability directly affect the potential for local adaptation. We studied in these populations the polymorphism at second exon of MHC class II. Analysis of gene flow at regional level did not detect a signal of selection. However, at the European level, positive selection at this locus strongly indicates that different pathogenic communities structure southern range populations from northern ones.
... The fact that females generally appear to be the choosiest sex in most animals may give rise to a bias in evolutionary research [9]. However some recent studies mentioned the occurrence of RCD in male mate preferences [10][11][12][13]. Occurrence of male mate choice in species from different taxa (actinopterygians, birds, insects, mammals) and contribution of female sexual traits and male choosiness to specific reproductive isolation [14,15] may indicate that this phenomenon is more common than previously thought. ...
... The local divergence of male mating calls of Hyla cinerea in ponds where H. gratiosa breeds syntopically [6] tends to support this idea. Additionally, cases have been reported where local adaptation in sexual behaviour persisted despite high gene flow [11,71]. ...
Reproductive character displacement is commonly described as larger phenotypic differences between species living in sympatry rather than in allopatry. We investigated this phenomenon on two amphibians found in their contact zone where syntopic and allotopic sites alternate. To test the effect of syntopy with Lissotriton vulgaris on the Lissotriton helveticus phenotype, we studied the morphology of adult males and females while controlling for environmental factors (i.e. land use and flood risk). Using linear mixed-effects models, we found that females of L. helveticus expressed a deeper tail when in the presence of the other species, a pattern consistent with reproductive character displacement. This pattern has been rarely observed in Amphibians. It suggests that male newts incur large mating costs when selecting heterospecific partners. Our study also emphasizes that the evolution of mate recognition systems could occur at a microgeographical scale within a sympatric area.
