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Journal Article

Rapid Origin of Sexual Isolation and Character Divergence in a Cline

Russell Lande
Evolution
Vol. 36, No. 2 (Mar., 1982), pp. 213-223
DOI: 10.2307/2408039
Stable URL: http://www.jstor.org/stable/2408039
Page Count: 11
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Rapid Origin of Sexual Isolation and Character Divergence in a Cline
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Abstract

Incipient speciation in a population occupying a continuous range is modeled as the joint evolution of geographic variation in female mating preferences and a quantitative secondary sexual character of males. Genetic variance in both traits is assumed to be maintained within local populations by polygenic mutation and recombination. Three types of polygamous mating systems are analyzed. The models show that sexual isolation and character divergence can originate rapidly over a wide geographic range, driven by genetic instability of the mating system in local populations. During this process, clines forming around a sharp ecological boundary are always monotonic. Even in the absence of genetic instability, the evolution of female mating preferences can greatly amplify large-scale geographic variation in male secondary sexual characters and produce widespread sexual isolation with no geographic discontinuity. These conclusions contrast with the popular conception that premating isolation is selected initially only in the contact zone between races to avoid deleterious hybridization, later spreading slowly if at all to other regions.

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