EFFECTS OF DIFFERENTIAL SELECTION IN THE SEXES ON CYTONUCLEAR POLYMORPHISM AND DISEQUILIBRIA

We develop a series of models that examine the effects of differential selection between the sexes on cytonuclear polymorphism and disequili bria. A detailed analysis is provided for populations under constant f ertility or viability selection censused at life stages without freque ncy differences in the sexes. We show analytically that cytonuclear di sequilibria can be generated de novo if the cytoplasmic and nuclear lo ci each affect female fitness and there is a nonmultiplicative fitness interaction between them. While computer simulations demonstrate that the majority of disequilibria produced by random selection are transi ent and small in magnitude, measurable permanent disequilibria can res ult from selective differences both within and between the two sexes. We derive analytic conditions for a protected cytonuclear polymorphism and use numerical simulations to quantitate the likelihood of obtaini ng permanent nuclear, cytoplasmic, and cytonuclear variation under var ious patterns of selection. The numerical analysis identifies special selection regimes more likely to generate disequilibria and maintain c ytonuclear polymorphism and reveals a direct correlation to the streng th of selection. As a byproduct, our models also provide the first dec omposition of the different parental contributions to cytonuclear dyna mics and the analytic conditions under which selection can cause cytop lasmic frequency changes or a cytonuclear hitchhiking effect.