Ornamental radiance as a defence against mimicry at the monogamy-polygyny interface.

Abstract

Ornament evolves though sexual selection when both monogamy or polygyny are equally viable. In this special situation monogamous females will be be able to reject unwanted polygynous suitors only if monogamous males are able distinguish themselves with a sign of fidelity. Since the most sexually advantageous trait value for any male to possess is the one that matches the mean female preference, any signs so created will persist when either monogamy or polygyny subsequently becomes a dominant strategy. Species will therefore accumulate traces of each passage through the monogamous-polygynous boundary which, in birds, can lead, among other outcomes, to a collage of patches of coloured plumage. If a species lives at the interface long enough a polygynous bird might be able to copy the sign of fidelity. One defence against this aggressive mimicry will be to evolve to a sign that is costly or difficult to copy. This process is modelled mathematically showing that if variation of female preference is increased the male phenotype will alter in unpredictable ways that defy a mimic, at a cost of possibly being maladapted. This causes an ornamental radiance that matches ideas of beauty in the human world.