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Pseudogamy as an Evolutionary Factor in the Poeciliid Fish Mollienisia formosa

Caryl P. Haskins, Edna F. Haskins and Richard E. Hewitt
Evolution
Vol. 14, No. 4 (Dec., 1960), pp. 473-483
DOI: 10.2307/2405996
Stable URL: http://www.jstor.org/stable/2405996
Page Count: 11
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Pseudogamy as an Evolutionary Factor in the Poeciliid Fish Mollienisia formosa
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Abstract

Preliminary findings are given in an investigation currently in progress of naturally occurring pseudogamous reproduction in the viviparous poeciliid fish Mollienisia formosa. Results obtained with crosses of this "all-female" form with the sympatric and normally bisexual species M. latipinna and M. sphenops confirm those of earlier workers: M. formosa females exhibited exclusively thelyotokous parthenogeny under sperm stimulus of these species, except in one interesting case, here reported, where introgression of a paternal characteristic from M. latipinna seems to have occurred. Results obtained in crosses to males of two more distantly related and allopatric forms, Limia nigrofasciata and Poecilia vivipara, showed similar apparent gynogenesis. With one race of Limia vittata, however, sexual reproduction proved the rule. The bisexual F1 progeny showed phenotypic similarity to and complete fertility with the male L. vittata parent. Males markedly predominated in the F1 progeny. Backcrosses of the F1 males to M. formosa resulted in mixed broods, with parthenogenetic females predominating in the first generation but rapidly being exceeded in numbers by their sexual siblings and their sexual descendants within three generations in mass culture. A fertile male, apparently phenotypically M. sphenops, developed among the isolated laboratory descendants (otherwise all M. formosa females) of individuals originally taken from a wild population of M. formosa. It is described and discussed in the context of the recent discovery of apparently naturally occurring males of M. formosa by Hubbs. Drewry, and Warburton. The possible evolutionary significance of these findings, and of those of Kallman on tissue transplantation within the species, is briefly considered.

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