Equal fecundity in asexual and sexual mollies (<Emphasis Type="Italic">Poecilia</Emphasis>)

The evolution and maintenance of sexual reproduction is still one of the major unresolved problems in evolutionary biology. Sexual reproduction is fraught with a number of costs as compared to asexual reproduction. For example, sexuals have to produce males, which–given a 1:1 sex ratio—results in a two-fold advantage for asexuals that do not produce males. Consequently, asexuals will outperform and replace sexuals over time assuming everything else is equal. Nonetheless, a few cases of closely related asexuals and sexuals have been documented to coexist stably in natural systems. We investigated the presence of a two-fold cost in a unique system of three closely related fish species: the asexual Amazon Molly (Poecilia formosa), and two sexual species, Sailfin Molly (P. latipinna) and Atlantic Molly (P. mexicana). Amazon Molly reproduce gynogenetically (by sperm dependent parthenogenesis) and always coexist with one of the sexual species, which serves as sperm donor. In the laboratory, we compared reproductive output between P. formosa and P. mexicana as well as P. formosa and P. latipinna. We found no differences in the fecundity in either comparison of a sexual and the asexual species. Under the assumption of a 1:1 sex ratio, the asexual Amazon Molly should consequently have a full two-fold advantage and be able to outcompete sexuals over time. Hence, the coexistence of the species pairs in nature presents a paradox still to be solved.     

Mating Preferences of the Gynogenetic Amazon Molly Differ Between Populations Sympatric with Different Host Species

Gynogenetic species rely on sperm from heterospecifics for reproduction but do not receive genetic benefits from mating because none of the paternal genome is incorporated into offspring. The gynogenetic Amazon molly (Poecilia formosa) is a species of hybrid origins that are sympatric with one of the two parent species that provide sperm for reproduction, P. latipinna or P. mexicana. Amazons should not prefer to mate with one species over the other because sperm from both species will trigger embryogenesis, but mating preferences may be present in Amazons through other mechanisms. Amazons may prefer the more familiar species (males found in sympatry), or Amazons may prefer males with the greatest lateral projection area (LPA), a preference that is present in the parent species and may be retained within the Amazon hybrid genome. We tested association preferences of two populations of Amazons sympatric with either P. mexicana or P. latipinna. We first performed live trials to test whether Amazons preferred one host species over the other and found that neither population of Amazons showed a preference. We then tested whether Amazons preferred sympatric male (familiar) host or the male with the greatest lateral projection area (LPA) using four animated male models that varied in host species and manipulation of LPA. We found Amazons from a population sympatric with P. latipinna showed no variation in their association preference across the different models. In contrast, Amazons from a population sympatric with P. mexicana (naturally small LPA) spent more time associating with the male models that had smaller LPA, which is more familiar to this population of Amazons. We suggest that Amazons may have population differences in mating preferences, where Amazons sympatric with P. latipinna may not show mating preference for host species, but Amazons sympatric with P. mexicana may show preferences for more familiar‐shaped males.     

ORIGIN AND MAINTENANCE OF A FEMALE MATING PREFERENCE

We investigated the role of maintenance and origin of female mating preferences in three species of fish. Poecilia latipinna and P. mexicana are sexual species that hybridized to form the gynogenetic clonal P. formosa, which reproduces asexually but requires sperm to initiate embryogenesis. We demonstrate that all three species display almost identical and statistically indistinguishable preferences for large males. Although processes of good genes, runaway sexual selection, and direct selection could maintain preferences in the sexual species, good genes and runaway sexual selection are unlikely to operate in the asexual species. Furthermore, we found that the most likely direct selection benefit, an increase in fecundity, can also be excluded in the gynogens. We conclude that the most parsimonious explanation for this P. formosa preference is that it was inherited from the parental species and is maintained without forces generated by good genes, runaway selection, or direct selection for increased fecundity. This preference may be maintained because of pleiotropic effects (e.g., sensory bias) or mate searching costs.     

The effect of rearing temperature on body shape and meristic characters in zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) juveniles

Considering its immediate costs of producing dispensable males, the maintenance of sexual reproduction is a major paradox in evolutionary biology. Asexual lineages that do not face such costs theoretically should replace sexuals over time. Nonetheless, several systems are known in which closely related sexual and asexual lineages stably coexist. In the present study, we studied a sexual/asexual mating complex of a sperm-dependent parthenogenetic fish (amazon molly, Poecilia formosa) and its sexual congeners, the sailfin molly P. latipinna and the Atlantic molly P. mexicana. We asked whether differences in feeding behavior could contribute to their stable coexistence. We conducted a laboratory experiment to compare feeding efficiencies and also measured the competitive abilities between the two reproductive forms. Additionally, we measured gut fullness of fishes caught in natural habitats. Contrary to our predictions, we could not find P. formosa to be less efficient in feeding. We argue that food competition in mollies plays a minor role in mediating coexistence between closely related asexual and sexual mollies.     

Juvenile survival in a unisexual/sexual complex of mollies

Unisexual species like the gynogenetic Amazon molly, Poecilia formosa, enjoy a twofold advantage over sexual species, because they do not produce males. Therefore, unisexuals should be able to outcompete and consequently, replace sexual species. For sperm-dependent (gynogenetic) unisexuals this creates a paradox: they cannot replace their sexual hosts without eradicating themselves. Thus, mechanisms must be in place to stabilize such mating systems. We assessed juvenile survivorship between asexual P. formosa and sexual Poecilia latipinna as a possible factor allowing for persistence and coexistence between the two sympatric species. Offspring of gynogenetic Amazon mollies did not differ significantly in survivorship compared to their sexual host, the Sailfin molly, P. latipinna. The presence of an adult female significantly reduced survival in both species, suggesting that filial cannibalisms operates in this system, but does not appear to play a role in stabilizing mixed sexual/asexual populations. Clark Hubbs, who spent 59 years at the University of Texas and was widely regarded as one of the state’s foremost researchers in the field of ichthyology, the study of fish, passed away February 3rd of 2008 after a long battle with colorectal cancer. He was 86.     

How to go extinct by mating too much: population consequences of male mate choice and efficiency in a sexual–asexual species complex

Selection acting on individuals is not predicted to maximize population persistence, yet examples that explicitly quantify conflicts between individual and population level benefits are scarce. One such conflict occurs over sexual reproduction because of the cost of sex: sexual populations that suffer the cost of producing males have only half the growth rate compared to asexuals. Male behaviour can additionally impact population dynamics in a variety of ways, and here we study an example where the impact is unusually clear: the riddle of persistence of sperm‐dependent sexual–asexual species complexes. Here, a sexually reproducing host species coexists with an ameiotically reproducing all‐female sperm parasite. Sexual–asexual coexistence should not be stable because the proportion of asexually reproducing females will rapidly increase and the relative abundance of the sexually reproducing host species will decline. A severe shortage of males will lead to sperm limitation for sexual and asexual females and the system collapses. Male mate choice could reduce the reproductive potential of the asexual species and thus potentially prevent the collapse. In the gynogenetic (sperm‐dependent parthenogenetic) Amazon molly Poecilia formosa and its host (P. latipinna or P. mexicana), males discriminate against asexual females to some extent. Using a population‐dynamical model, we examine the population dynamics of this species complex with varying strengths of male discrimination ability and efficiency with which they locate females and produce sperm. The sexual species would benefit from stronger discrimination, thus preventing being displaced by the asexual females. However, males would be required to evolve preferences that are probably too strong to be purely based upon selection acting on individuals. We conclude that male behaviour does not fully prevent but delays extinction, yet this is highly relevant because low local extinction rates strongly promote coexistence as a metapopulation.     

Character displacement in sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>: allozymes and behavior

Synopsis 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 induce embryogenesis but inheritance is strictly maternal. Where sailfin and Amazon mollies are sympatric there is evidence of reproductive character displacement as males show a significantly stronger mating preference for sailfin molly females over Amazon mollies compared to preferences of males from allopatric populations. From the allozyme data we found a moderate amount of genetic variation across all populations but this variation did not reveal significant partitioning between sympatric and allopatric populations. Additionally, we found no evidence for isolation by distance as genetic distance was not significantly correlated with geographic distance. While allozyme variation also did not significantly correlate with male mating preferences, there was a significant correlation between male mating preferences and geographic distance. This correlation between mating preferences and geographic distance may have arisen from coevolution with Amazon mollies resulting in reproductive character displacement. Taken together, the distribution of genetic and behavioral variation among sympatric and allopatric populations suggests that behavioral evolution has outpaced evolution at the allozyme loci we examined in P. latipinna.     

Do I Know You? Species Recognition Operates Within and Between the Sexes in a Unisexual–Bisexual Species Complex of Mollies

Male sailfin mollies (Poecilia latipinna) can be sexually parasitized by closely related, unisexual, gynogenetic Amazon mollies (Poecilia formosa). This study examined possible cues used by male P. latipinna to distinguish between conspecific females and sympatric, heterospecific P. formosa. Digital photos were used to create models to test male P. latipinna preference for model female P. latipinna and P. formosa with a full suite of traits and altered models of P. latipinna and P. formosa. Male P. latipinna significantly preferred models of either species over no stimulus, demonstrating that models elicit a male response. Males also significantly preferred female P. latipinna models over P. formosa models. We also examined species recognition by female sailfin mollies using the same models, and found that female sailfin mollies significantly preferred to associate with female P. latipinna over P. formosa. These results taken together suggest that the use of fish models yield results similar to those studies using live stimuli. Male preference was then tested for unaltered vs. altered models in the following combinations: (i) P. formosa vs. P. formosa with a female P. latipinna fin; (ii) P. formosa vs. P. formosa with a female P. latipinna lateral spot pattern; (iii) P. formosa vs. P. latipinna with a P. formosa fin and their spotless lateral pattern. Males did not significantly prefer models with any isolated traits over the unaltered P. formosa models. Thus, males may be using traits other than the ones isolated for species recognition or males may be using a suite of multiple traits to recognize conspecific females.     

Male Mate Choice in Mixed Bisexual/Unisexual Breeding Complexes of Poecilia (Teleostei: Poeciliidae)

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.     

Are you more than the sum of your parents’ genes? Phenotypic plasticity in a clonal vertebrate and F1 hybrids of its parental species

All known vertebrate clones have originated from hybridization events and some have produced distinct evolutionary lineages via hybrid speciation. Amazon mollies (Poecilia formosa) present an excellent study system to investigate how clonal species have adapted to heterogeneous environments because they are the product of a single hybridization event between male sailfin mollies (Poecilia latipinna) and female Atlantic mollies (Poecilia mexicana). Here, we ask whether the hybrid species differs from the combination of its parental species’ genes in its plastic response to different environments. Using a three-way factorial design, we exposed neonates produced by Amazon mollies and reciprocal F1 hybrid crosses to different thermal (24°C and 29°C) and salinity (0/2, 12, and 20 ppt) regimes. We measured various ontogenetic and life history characteristics across the life span of females. Our major results were as follows: (1) Reaction norms of growth and maturation to temperature and salinity are quite similar between the two hybrid crosses; (2) Amazon molly reaction norms were qualitatively different than the P. latipinna male and P. mexicana female (L×M) hybrids for the ontogenetic variables; (3) Amazon molly reaction norms in reproductive traits were also quite different from L×M hybrids; and (4) The reaction norms of net fertility were very different between Amazon mollies and L×M hybrids. We conclude that best locale for Amazon mollies is not the best locale for hybrids, which suggests that Amazon mollies are not just an unmodified mix of parental genes but instead have adapted to the variable environments in which they are found. Hybridization resulting in asexuality may represent an underappreciated mechanism of speciation because the unlikely events required to produce such hybrids rarely occur and is dependent upon the genetic distance between parental species.     

Differential susceptibility to food stress in neonates of sexual and asexual mollies (<Emphasis Type="Italic">Poecilia</Emphasis>, Poeciliidae)

The maintenance of sex is still an evolutionary puzzle given its immediate costs. Stably coexisting complexes of asexually and sexually reproducing forms allow to study mechanisms that balance the costs and benefits of both asexual and sexual reproduction. Here, we tested whether coexisting asexual and sexual fish of the genus Poecilia differed in neonate mortality when exposed to environmental stress in the form of fluctuating temperatures and food deprivation. We find that asexual Amazon mollies, Poecilia formosa, are significantly more sensitive to food stress than their sexual relative Poecilia latipinna, but both are equally unaffected by variable temperatures. Differences in the susceptibility to environmental stress may contribute to diminishing the asexuals’ benefits of a higher intrinsic population growth rate and thus mediate stable coexistence of the two reproductive forms.     

Lack of species discrimination based on chemical cues by male sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>

When making mating decisions, individuals may rely on multiple cues from either the same or multiple sensory modalities. Although the use of visual cues in sexual selection is well studied, fewer studies have examined the role of chemical cues in mate choice. In addition, few studies have examined how visual and/or chemical cues affect male mating decisions. Male mate choice is important in systems where males must avoid mating with heterospecific females, as is found in a mating complex of Poecilia. Male sailfin mollies, Poecilia latipinna, are sexually parasitized by gynogenetic Amazon mollies, P. formosa. Little is known about the mechanism by which male sailfin mollies base their mating decisions. Here we tested the hypothesis that male sailfin mollies from an allopatric and a sympatric population with Amazon mollies use multiple cues to distinguish between conspecific and heterospecific females. We found that male sailfin mollies recognized the chemical cues of conspecific females, but we found no support for the hypothesis that chemical cues are by themselves sufficient for species discrimination. Lack of discrimination based on chemical cues alone may be due to the close evolutionary history between P. latipinna and P. formosa. Males from populations sympatric with Amazon mollies did not differentially associate with females of either of the two species when given access to both visual and chemical cues of the females, yet males from the allopatric population did associate more with conspecific females than with heterospecific females in the presence of both chemical and visual cues. The lack of discrimination by males from the sympatric population between conspecific and heterospecific females based on both chemical and visual cues suggests that these males require more complex combinations of cues to distinguish species, possibly due to the close relatedness of these species.     

Patterns of inheritance of mating signals in interspecific hybrids between sailfin and shortfin mollies (Poeciliidae: Poecilia: Mollienesia)

Differences in male morphology and mating behaviors are thought to confer species sexual isolation between sailfin and shortfin species of mollies. This study used interspecific crosses between the sailfin molly, P. latipinna, and the shortfin molly, P. mexicana, to investigate patterns of inheritance of morphological traits and behavioral rates of three mating behaviors in F1 hybrid males. The two parental species showed clear species differences with respect to the length of the dorsal fin and dorsal fin ray number. First generation hybrid males were intermediate between the two parental species for dorsal fin length and fin ray number, suggesting autosomal control of this trait with little effect of dominance by genes from either parental species. Parental species showed clear species differences in their rates of courtship displays. Unlike the pattern for dorsal fin morphology, F1 hybrid males showed a clear distinction in display rates with respect to the direction of the interspecific cross. Male hybrids whose sires were P. latipinna had courtship display rates that were up to three times higher than the rates of displays performed by hybrid males whose fathers were P. mexicana. The distribution of phenotypes between the parental species and that of hybrid males sired by that parental species was nearly identical. Such a pattern suggests the influence of Y-linked genes on the inheritance of courtship display rates in mollies.     

HYBRIDIZATION LEADS TO SENSORY REPERTOIRE EXPANSION IN A GYNOGENETIC FISH,THE AMAZON MOLLY (POECILIA FORMOSA): A TEST OF THE HYBRID‐SENSORY EXPANSION HYPOTHESIS

Expansions in sensory systems usually require processes such as gene duplication and divergence, and thus evolve slowly. We evaluate a novel mechanism leading to rapid sensory repertoire expansion: hybrid‐sensory expansion (HSE). HSE occurs when two species with differently tuned sensory systems form a hybrid, bringing together alleles from each of the parental species. In one generation, a sensory repertoire is created that is the sum of the variance between parental species. The Amazon molly presents a unique opportunity to test the HSE hypothesis in a “frozen” hybrid. We compared opsin sequences of the Amazon molly, Poecilia formosa, to those of the parental species. Both parental species are homozygous at the RH2–1 locus and each of the four long wavelength sensitive loci, while P. formosa possess two different alleles at these loci; one matching each parental allele. Gene expression analysis showed P. formosa use the expanded opsin repertoire that was the result of HSE. Additionally, behavioral tests revealed P. formosa respond to colored stimuli in a manner similar or intermediate to the parental species P. mexicana and P. latipinna. Together these results strongly support the HSE hypothesis. Hybrid‐sensory repertoire expansion is likely important in other hybrid species and in other sensory systems.     

Cytogenetic studies of Poecilia (Pisces)

Natural populations of triploid females resembling the gynogenetic teleost, Poecilia formosa (Girard), occur in northeastern Mexico where they intermingle with diploid populations of this species and the members of congeneric bisexual species such as P. mexicana or P. latipinna. Mitotic configurations from gill epithelial cells show 46 chromosomes for the diploid fishes, but 69 chromosomes for members of the triploid clones associated with P. formosa. Triploid females have erythrocytes that are significantly larger than those from diploid specimens and also show a roughly 50% elevation in the average DNA content of their somatic nuclei. Similar analyses of two functionally incompetent males of P. formosa, of a number of bisexual F₁ and F₂ hybrid offpsring from P. latipinna x P. mexicana, and of females from several other poeciliid species consistently show only diploid DNA levels and somatic chromosome complements where 22N=46. Demonstration of cytogenetic criteria by which females from triploid clones may be clearly distinguished from sympatric diploid specimens of P. formosa or P. mexicana leaves unresolved, for the present, problems of an appropriate systematic designation for natural populations of triploid gynogenetic fishes. The role of sympatric speciation in the evolution of poeciliid genomes is discussed in terms of alternative mechanisms to account for the persistence in nature of a vertebrate triploid of hybrid origin.This work was supported by grants from the National Science Foundation (GB 7393) and from the U.S. Public Health Service (GM 14644).Recipient of a Research Career Development Award from the U.S. Public Health Service (1 K3 GM 3455).     

Female Preference for Male Lateral Projection Area in the Shortfin Molly, Poecilia mexicana: Evidence for a Pre-existing Bias in Sexual Selection

Sailfin molly (Poecilia latipinna) males possess a large dorsal fin (sailfin) and perform an elaborate courtship display. Females prefer to associate and mate with males of greater body and sailfin size. Evidence supports a single origin for the sailfin species complex from a shortfin ancestor. Unlike sailfin species, males of the shortfin species complex are sexually monomorphic in fin size and exhibit little or no courtship behavior. In this study, we tested the pre‐existing bias and lateral projection area (LPA) hypotheses for sexual selection by examining female mating preferences in the shortfin molly, P. mexicana. Specifically, we presented females with pairs of dummy males differing in: (1) dorsal fin and body size together (holding fin:body size ratio constant); (2) body size (holding dorsal fin size constant); (3) dorsal fin size (holding body size constant); and dorsal fin:body size ratio (holding total LPA constant). Females spent more time near dummies of greater body and dorsal fin size. The preference functions based on the first three sets of stimuli showed a similar pattern: the greater the LPA difference between paired dummies, the stronger the preference for the larger of the two. However, in the fourth experiment, neither fin size, body size, nor any particular dorsal fin + body size combination was preferred. These findings support the LPA hypothesis suggesting that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. Moreover, these data are consistent with results obtained in an identical series of experiments conducted on P. latipinna. The preference for increased male dorsal fin size/LPA by both female P. latipinna and P. mexicana supports the pre‐existing bias hypothesis. Thus, a bias for increased male LPA and consequent selection for enlarged dorsal fins may have preceded the appearance of the sailfin trait within the Molliensia lineage.     

Biogeography of the Amazon molly: ecological niche and range limits of an asexual hybrid species

Aim To understand the relative contributions of environmental factors, dispersal limitations and the presence of sperm donors in determining the distribution of the Amazon molly (Poecilia formosa), a sperm‐dependent unisexual fish species of hybrid origin. To explore niche similarities and/or differences between the hybrid and parental species. To evaluate whether large‐scale abiotic factors can explain a successful introduction of both P. formosa and Poecilia latipinna. Location South‐east United States, Mexico and Central America. Methods We used abiotic variables in ecological niche modelling (ENM) to identify regions with suitable conditions for the presence of the Amazon molly and its two parental species (P. latipinna and Poecilia mexicana). We also used a recently developed metric to calculate the degree of niche overlap between the hybrid and its parental species. Results ENM produced highly significant models [all area under the curve (AUC) > 0.99 for the three species]. Annual mean temperature and minimum temperature of the coldest month were the variables that best explained the distribution of the Amazon molly. With the exception of south Florida, few areas beyond the known distribution of the species were predicted to have suitable environmental conditions. The hybrid species niche overlaps partially with the parental species. However, given the available data, it is neither more similar nor more different than expected by chance. Main conclusions Two different processes are acting to limit the distribution of P. formosa. At the northern limit, although a sperm donor species is present further north, suitable environmental conditions are absent from nearby locations. At the southern limit, a sperm donor species is present and areas with good environmental conditions are present at nearby locations, suggesting that dispersal ability is the limiting factor. We found that the hybrid species overlaps in a similar way with both parental species while still having its own niche identity. This result may be explained by the fact that hybrid species inherit characteristics of two ecologically divergent species, which can result in intermediate or even transgressive phenotypes. These results support recent work on the role of hybridization in diversification.     

Effects of Female‐Female Aggression in a Sexual/Unisexual Species Complex

The maintenance of sexual reproduction is still a largely unresolved question in evolutionary biology, and one of the most puzzling aspects of this is the coexistence of sexual and asexual females. This often leads to widespread niche overlap, posing an interesting challenge to competitive exclusion theory. In this study, we investigate how the aggressive behaviors between females in a sexual/unisexual mating complex of mollies (Poecilia latipinna and P. formosa) differ, and the effects these behaviors have on both the performer and receiver of aggressive acts. We exposed females to five treatments: (1) alone (control); (2) a large and small sexual female; (3) a large sexual female and a small unisexual female; (4) a small sexual female and a large unisexual female; and (5) a large and small unisexual female. We found that P. formosa females were on average more aggressive over time when compared to their sexual hosts, P. latipinna. The females of P. formosa, however, incurred a higher cost of being aggressive. Large, aggressor females of this species had a lower body fat content than their conspecific recipients. By contrast, P. latipinna females showed no differentiation between aggressors and recipients. Here, we combine life history methodology and behavioral observations to show that female competition can in fact be quantitatively measured and that these aggressive behaviors are costly to perform. The adaptive value of this interspecies aggression is not yet completely understood, but sexual competition, access to resources, and position within the shoal are all possible functions.     

Behavioural and life‐history regulation in a unisexual/bisexual mating system: does male mate choice affect female reproductive life histories?

In theory, unisexual taxa have an advantage over ecologically similar bisexual species because unisexuals produce twice as many daughters and, thus, should quickly outcompete coexisting bisexuals in any given population. For sperm‐dependent unisexual (gynogenetic) species, stable coexistence with their bisexual sperm donors can be postulated if male mate choice puts unisexual females at a disadvantage through sperm limitation, thus halving their reproductive output compared to bisexuals (‘behavioural regulation hypothesis’). We tested for a potential life‐history signature of male mate choice in a system of coexisting bisexual sailfin mollies (Poecilia latipinna) and gynogenetic Amazon mollies (Poecilia formosa). Specifically, we gave P. latipinna males an opportunity to freely interact (and mate) with both types of females and, after 25 days, quantified the proportion of (1) females with sperm in their genital tract and (2) pregnant females. A higher proportion of P. latipinna females (53.7%) had sperm in their genital tract (compared to only 25.9% in P. formosa), corroborating a previous study on wild‐caught fish. This translated into a higher frequency (42.6%) of P. latipinna females being pregnant (compared to 29.6% in P. formosa); however, among pregnant females, no significant differences between species in reproductive life‐history traits (such as offspring number or size) were uncovered. Hence, although the findings of the present study confirm that male discrimination against unisexual females leads to reduced reproductive output in unisexuals, the observed magnitude of differences in targeted life histories between the two types of females is unlikely to be the sole factor regulating stable coexistence in this system. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 598–606.     

Examination of boldness traits in sexual and asexual mollies (<Emphasis Type="Italic">Poecilia latipinna</Emphasis>, <Emphasis Type="Italic">P. formosa</Emphasis>)

Considering the high costs of sexual reproduction (e.g., the production of males), its maintenance and predominance throughout the Animal Kingdom remain elusive. Especially the mechanisms allowing for a stable coexistence of closely related sexual and asexual species are still subject to a lively debate. Asexuals should rapidly outnumber sexuals due to higher population growth rates, unless they face some disadvantages. Here, we investigate potential differences in feeding behavior in a system of sexual (sailfin mollies, Poecilia latipinna) and coexisting gynogenetic fishes (Amazon mollies, Poecilia formosa). In two different experiments, we tested for differences in behavioral traits associated with boldness. Bold individuals take higher risks for gains in resources, so shyer individuals should be less competitive. Our study was motivated by the recent finding that P. formosa are less likely to be preyed upon by piscine predators than P. latipinna. We asked whether this result is indicative of low boldness in P. formosa. However, no differences between the two species were detectible in our behavioral experiments measuring (a) time to emerge from shelter to explore a novel environment, (b) latency time until feeding in a novel environment, and (c) recovery time until feeding restarted after a simulated predator attack. Furthermore, different boldness measures were not correlated with each other within individuals.