The co-evolution of multiple female mating preferences and preferred male characters: The "gene-for-gene" hypothesis of sexual selection

The males of some animals possess a number of characters that may have evolved because they are preferred by females in mating. Some of these characters are exaggerations of corresponding female traits and may be under polygenic control. Other characters appear to show discrete or discontinuous variation between males and females; these traits often make the male phenotype more elaborate and may be controlled by single loci. We propose the "gene-for-gene" hypothesis of sexual selection to account for the evolution of multiple male ornaments that differ discontinuously from their female counterparts: each male trait, controlled by a single locus, has a corresponding female preference, also controlled by a single locus. Each character and its preference might have evolved sequentially; alternatively, more than one such combination might have evolved more or less at the same time. To analyse the latter possibility, we have constructed a "gene-for-gene" model of the simultaneous co-evolution of two preferred characters and their preferences. Simulations show that large genetic interactions can arise between different combinations of character and preference, usually if one character is deleterious and the other is advantageous. "Gene-for-gene" models may hereby promote the co-evolution of deleterious male ornaments and their preferences. The simultaneous co-evolution of preferences and male traits is therefore a serious and important alternative to sequential evolution. The "gene-for-gene" hypothesis may explain the evolution of some of the male ornaments of animals like peacocks, ruffs, domestic fowls and pheasants. It might also apply to characters thought to be the preserve of polygenic models. © 1989 Academic Press Limited.