Evidence for a monophyletic origin of triploid clones of the Amazon molly, Poecilia formosa.

Department of Physiological Chemistry I, University of Wuerzburg, Biozentrum, Am Hubland, 97074 Wuerzburg, Germany.
Evolution (Impact Factor: 4.86). 05/2005; 59(4):881-9. DOI: 10.1554/04-453
Source: PubMed

ABSTRACT Asexual reproduction in vertebrates is rare and generally considered an evolutionary dead end. Asexuality is often associated with polyploidy, and several hypotheses have been put forward to explain this relationship. So far, it remains unclear whether polyploidization in asexual organisms is a frequent or a rare event. Here we present a field study on the gynogenetic Amazon molly, Poecilia formosa. We used multilocus fingerprints and microsatellites to investigate the genetic diversity in 339 diploid and 55 triploid individuals and in 25 P. mexicana, its sexual host. Although multilocus DNA fingerprints found high clonal diversity in triploids, microsatellites revealed only two very similar clones in the triploids. Phylogenetic analysis of microsatellite data provided evidence for a monophyletic origin of the triploid clones of P. formosa. In addition, shared alleles within the triploid clones between the triploid and diploid genotypes and between asexual and sexual lineages indicate a recent origin of triploid clones in Poecilia formosa.

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    ABSTRACT: 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. KeywordsPoeciliid-Asexual-Recombination-Fecundity
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    ABSTRACT: 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.
    Evolutionary Ecology 01/2010; 24(1):39-47. · 2.41 Impact Factor
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    ABSTRACT: The gynogenetic livebearing Amazon molly (Poecilia formosa) is a sexual parasite that exploits males of closely related species for sperm. This is needed as physiological stimulus for embryo development; however, none of the male’s genes are normally incorporated into the genome of the gynogenetic offspring. Mostly diploid individuals were reported from the natural habitats in North-Eastern Mexico and South-Eastern Texas but stable populations of triploids have been reported from the Río Soto la Marina drainage and in the Río Guayalejo in North-Eastern Mexico. Triploidy is the result of defects in the mechanisms that normally clear the host sperm from the ameiotic diploid egg. Triploids also reproduce gynogenetically and their frequencies fluctuate markedly between years, seasons, and localities. To understand the dynamics of this mating system, it is important to understand the relative reproductive success of triploids and diploids. We hypothesize that triploids should have a selective advantage over diploids due to heterosis and/or gene redundancy based on the additional genetic material from the sexual host. However, clonal competition experiments revealed a clear reproductive advantage of diploids competing with triploids. This result contradicts not only our hypothesis but also the stable co-existence of diploids and triploids in natural habitats. Frequency dependent selection, niche partitioning and environmental heterogeneity are discussed as possible explanations.
    Evolutionary Ecology 01/2009; 23(5):687-697. · 2.41 Impact Factor


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Jun 28, 2014