SEX AND SALTATION IN THEORETICAL POPULATIONS

Sexual selection and adaptive shifts are important agents of evolutionary radiation. Three classes of population genetic models are presented here which investigate the consequences of these processes.

The first is a study of the joint evolution of a mating system involving a male secondary sexual character that affects survivorship and a female mating preference for that trait. It is assumed here that males contribute gametes but not material benefits to their mates and offspring. The major conclusion reached is that selection does not eliminate female preferences for less viable males, but instead the preferences and the less viable male forms can persist in equilibrium.

A second class of models studies the effect that a material contribution by males to their mates has for a sexually selected mating system. Results show that female mating behavior evolves to maximize female fecundity. This finding refutes the so-called "sexy son" hypothesis of sexual selection, which contends that females may be selected to mate with males that decrease their fecundity if their sons then receive the genes for the male's sexually attractive traits.

Lastly, models of a form of natural selection that results in rapid evolutionary shifts from one adaptive state to another are analysed. Conditions for adaptive shifts are more general than had been previously believed. The models exhibit behavior that is analogous to the "punctuated equilibria" mode of evolution seen in the fossil record, suggesting that the mechanisms described by the models may play a role in producing the observed patterns.