Local mate competition with variable fecundity: dependence of offspring sex ratios on information utilization and mode of male production

Abstract

Most models of local mate competition assume that the foundresses contributing offspring to a local mating group (‘patch’) all have the same fecundity. Frank (1985, 1987a, b), Herre (1985), and Yamaguchi (1985) consider models with variable fecundity, in which foundresses adjust their sex allocations in response to the fecundities of the other foundresses in the patch. Here we generalize and extend these models to include cases in which females can respond to their own fecundities but not to each other's (possibly because they must determine their sex allocations before they arrive at the patch) and cases in which siblings avoid mating with each other. Evolutionarily stable sex-allocation phenotypes are derived through both inclusive-fitness and population-genetic approaches. Each model is solved for haploid, diploid, and haplodiploid genetic systems with biparental and arrhenotokous modes of male production. In models that allow sibmating, the biparental genetic systems have one evolutionarily stable strategy (ESS) and the arrhenotokous systems have another, but within each of these categories, all three ploidys have the same ESS. Where females can respond only to their own fecundities, their brood sex Tratios decline with increasing brood size, but their absolute investments in males increase; this response occurs even where the mean patch size is very large and the mean sex ratio of parental investment is therefore indistinguishable from one-half. Patterns of sex allocation in many kinds of spatially structured populations may depend critically on the ways in which females perceive and respond to environmental features that predict the fitness distributions of their local mating aggregations.