Abstract
Sexual dimorphism is typically thought to result from sexual selection for elaborated male traits, as proposed by Darwin. However, natural selection could reduce expression of elaborated traits in females, as proposed by Wallace. Darwin and Wallace debated the origins of dichromatism in birds and butterflies, and although evidence in birds is roughly equal, if not in favor of Wallace's model, butterflies lack a similar scale of study. Here, we present a large‐scale comparative phylogenetic analysis of the evolution of butterfly coloration, using all European non‐hesperiid butterfly species (n = 369). We modeled evolutionary changes in coloration for each species and sex along their phylogeny, thereby estimating the rate and direction of evolution in three‐dimensional color space using a novel implementation of phylogenetic ridge regression. We show that male coloration evolved faster than female coloration, especially in strongly dichromatic clades, with male contribution to changes in dichromatism roughly twice that of females. These patterns are consistent with a classic Darwinian model of dichromatism via sexual selection on male coloration, suggesting this model was the dominant driver of dichromatism in European butterflies.
Highlights
Males and females of many species are dimorphic; there are differences in the way the sexes look and function
Conspicuous colors in general, and sexual dichromatism in particular, proved to be early problems for Darwin’s theory of natural selection, as no obvious advantage seemed to be gained by having them (Kottler 1980)
By comparing the lengths of the male and female evolutionary vectors, we investigated which sex has a higher rate of color evolution
Summary
Males and females of many species are dimorphic; there are differences in the way the sexes look and function. Charles Darwin argued that sexual selection drives male color away from female color, whereas contemporary Alfred Russel Wallace instead thought that natural selection pulled female color away from the male’s We revisit this debate using butterflies, one of the taxa Darwin and Wallace argued over, to determine whether Darwin’s or Wallace’s model is more important in the evolution of dichromatism. Conspicuous colors in general, and sexual dichromatism (sexes differing in color) in particular, proved to be early problems for Darwin’s theory of natural selection, as no obvious advantage seemed to be gained by having them (Kottler 1980) Darwin expanded his other theory, sexual selection, to include the elaboration of traits through selection by female preference for conspicuous males (Darwin, 1871). In the taxon best studied, Darwin’s model for dichromatism appears to be the exception rather than the rule, calling into question the general assumption that sexual selection is the primary agent generating dichromatism in other colorful clades
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