Theoretical studies of the evolution of male display by sexual selection.

Abstract

In this study I present a new mechanism for the evolution of male display as a consequence of female choice. I use a population genetic model to show that if female preferences for better males are based on a cue that is an integral part of male adaptation, a display may evolve if it amplifies the variance in this cue, and hence increases female resolution power with respect to male quality. This evolutionary mechanism is used as a core of a theory that explains the evolution of male display and adaptive female choice (i.e. female preferences that evolve because of their association with high quality genes). I argue that because an amplifying display (termed "amplifier") decreases mating success of males of poor quality, modifiers are likely to evolve that decrease the expression of the amplifier when associated with the poor quality males. As a result, the amplifier's expression becomes an indicator of male quality, and provides sufficient conditions for the evolution of a new type of female choice that is based on the amplifier's expression. This process may lead, in turn, to further changes in both female choice and male display, emphasizing either the amplifying effect of displays or their indicating effect. I show that the direction of these changes may depend on the cost that the amplifier confers on male viability, and on the degree of polygyny of the mating system in concern. I also outline explicit predictions for empirical tests.