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Origin of Thermal Adaptations in Northern Versus Southern Populations of a Unisexual Hybrid Fish

Arthur J. Bulger and R. Jack Schultz
Evolution
Vol. 36, No. 5 (Sep., 1982), pp. 1041-1050
DOI: 10.2307/2408081
Stable URL: http://www.jstor.org/stable/2408081
Page Count: 10
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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.
Origin of Thermal Adaptations in Northern Versus Southern Populations of a Unisexual Hybrid Fish
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Abstract

Hemiclones of the unisexual fish Poeciliopsis monacha-occidentalis are not better adapted to cold temperatures in the northern part of their range than in the southern part of their range, nor is there conclusive evidence that they are coadapted to local populations of the sexual host species, P occidentalis. Response of the introgressed monacha genome to thermal stress is not clinal, whether the maternal genome is combined with a paternal genome of P. occidentalis or of P lucida; in fact, the differences in response among populations from the five river systems tested were of the same magnitude as from among hemiclones within the Rio Mayo, the southernmost river and the apparent site of origin of P monacha-occidentalis. Although the resistance to cold stress exhibited by P. monacha-occidentalis may play a role in its survival in the north, and heterosis for resistance to heat stress may contribute to its success in the south, these traits more likely derive from the original hybrid genotypes than from adaptive changes subsequent to their hybrid origin. Thus, it remains to be demonstrated that unisexual Poeciliopsis in the absence of a mechanism for recombination, have the capacity to evolve.

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