Abstract

Abstract Ultimately based on the different gamete size and the resulting sex roles, most animal species have acquired traits that occur only in one of the sexes. For those sex-limited traits the impact of a single selection event is reduced, because the genes coding for these traits also occur unexpressed in the other sex and are therefore partly hidden to selection. All sex-limited traits thus show a storage effect analogous to a seed bank. This storage effect has to be considered when measuring the effect of fluctuating selection on sex-limited traits. Here, I develop appropriate equations to measure the ability of an allele to invade a population when fluctuating selection acts on sex-limited traits. A comparison of the equations for X-chromosomal and autosomal traits gives the following result: the evolution of traits limited to the heterogametic sex should preferentially involve X-chromosomal genes and the evolution of traits limited to the homogametic sex should preferentially involve autosomal genes. This difference between the sexes may contribute to explain (1) the large effect of X-chromosomal genes in causing hybrid sterility in the heterogametic sex and (2) the large effect of X-chromosomal genes on sexually selected traits in heterogametic males.

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