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Ecological and Evolutionary Relationships Among Diploid and Triploid Unisexual Fishes Associated with the Bisexual Species, Poeciliopsis lucida (Cyprinodontiformes: Poeciliidae)

Roger E. Thibault
Evolution
Vol. 32, No. 3 (Sep., 1978), pp. 613-623
DOI: 10.2307/2407727
Stable URL: http://www.jstor.org/stable/2407727
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ecological and Evolutionary Relationships Among Diploid and Triploid Unisexual Fishes Associated with the Bisexual Species, Poeciliopsis lucida (Cyprinodontiformes: Poeciliidae)
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Abstract

1. Information on differential reproduction, distribution and abundance of diploid and triploid unisexual fishes of the genus Poeciliopsis was utilized to evaluate the evolutionary potential of each form as progenitor to a hypothetical tetraploid species. 2 Unisexuals from natural populations of the Rio del Fuerte of Sonora and Sinaloa, Mexico, were identified by erythrocyte diameters (N = 231). The triploid gynogen, common at all five sampling stations, is distributed throughout the river system and not restricted to a single tributary as was heretofore believed. 3. Unisexual frequencies were determined at three localities during both winter and spring sampling periods (N = 7). Diploids were usually more abundant than triploids, but triploids were on the increase as the dry season progressed and outnumbered diploids at one locality in May Unisexual Poeciliopsis may divide the habitat temporally as is believed to occur among unisexuals in the Poecilia formosa complex. 4 In the laboratory, diploids produced more than twice as many young as triploids. In nature, however, triploids are slightly more fecund and a greater number of them are inseminated in comparison to the diploid hybridogens. Mature diploid and triploid unisexuals do not differ in size. 5 Components of diploid and triploid fitness are qualitatively compared using a model developed by Moore (1976). This research lends support to the hypothesis that triploidy in vertebrates may not be an evolutionary dead end. Triploid Poeciliopsis are, at the least, equal contenders with their diploid competitors.

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