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Ecological Causes of Sexual Dimorphism
Vol. 38, No. 3 (May, 1984), pp. 622-630
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2408711
Page Count: 9
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There are several ecological mechanisms that could account for the origin of sexual dimorphism in a dioecious species that is initially monomorphic. Ecological conditions could favor different characteristics in each sex as a consequence of different ecological or social roles (dimorphic niche). ecological conditions could favor two distinct types of individuals of either sex (bimodal niche), or ecological conditions could favor dimorphism through competition in a manner analogous to ecological character displacement (competitive displacement). A model of a quantitative character evolving under each of these assumptions is introduced and analyzed. If there is a unique equilibrium of the population, as in the case of a dimorphic niche or competitive displacement, the extent of genetic correlation between the sexes does not affect the likelihood of a species evolving a sexual dimorphism. The ecological forces alone will determine whether or not a dimorphism can evolve. If there there are several stable equilibria, as is true for the bimodal niche, then the genetic correlations among the sexes in the trait of interest will determine which equilibrium is reached. In that case, the conditions under which dimorphism will evolve in a species that is initially nearly monomorphic are restrictive.
Evolution © 1984 Society for the Study of Evolution