Sex Ratio Strategies After Perturbation of the Stable Age Distribution

Animals with overlapping generations may be selected to change their sex ratios after perturbation of the stable age distribution. Specifically, Werren and Taylor have shown that in a tightly regulated population with normally constant recruitment, sex ratios are based at times of exceptional recruitment towards the sex with the most even distribution of reproductive value over its adult life. It is shown that an episode of exceptional recruitment also affects the optimal sex ratios of cohorts born subsequently, although the sex ratio adjustment is typically in the opposite direction. It is also shown that the expected sex ratio depends critically on female mating behaviour: whether females mate throughout their reproductive life or, as in many insects, once after emergence. Perturbation of the stable age distribution by an episode of exceptional mortality may also lead to selection for biased sex ratios, even if the mortality affects both sexes equally.