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Heterosis and Interclonal Variation in Thermal Tolerance in Unisexual Fishes

Arthur J. Bulger and R. Jack Schultz
Evolution
Vol. 33, No. 3 (Sep., 1979), pp. 848-859
DOI: 10.2307/2407650
Stable URL: http://www.jstor.org/stable/2407650
Page Count: 12
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Heterosis and Interclonal Variation in Thermal Tolerance in Unisexual Fishes
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Abstract

Hybridization in nature between Poeciliopsis monacha and P. lucida has resulted in diploid and triploid all-female populations which are self-replicating, and extremely successful, outnumbering their parental species at some localities by as much as 20:1 (Schultz, 1977). Their habitats in the streams of northwestern Mexico are characterized by thermal fluctuations sufficiently extreme to affect the local success of fish populations. Two unusual reproductive mechanisms (gynogenesis or hybridogenesis) in hybrids perpetuate their highly heterozygous F1 genotypes generation after generation. Tests of thermal tolerance in the two bisexual species and their unisexual hybrids demonstrated both heterosis and presumably adaptive interclonal variation in thermal characteristics among the clones and hemiclones which make up populations of these hybrids. Heterosis and interclonal variation may contribute to hybrid success by increasing niche width, heterosis by increasing the range of conditions invidivuals can tolerate, and interclonal variation by diversifying the population's thermal adaptations.

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