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

Most models of local mate competition assume that the foundressescontributing 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 responseto the fecundities of the other foundresses in the patch. Herewe generalize and extend these models to include cases in whichfemales can respond to their own fecundities but not to eachother's (possibly because they must determine their sex allocationsbefore they arrive at the patch) and cases in which siblingsavoid mating with each other. Evolutionarily stable sex-allocationphenotypes are derived through both inclusive-fitness and population-geneticapproaches. Each model is solved for haploid, diploid, and haplodiploidgenetic systems with biparental and arrhenotokous modes of maleproduction. In models that allow sibmating, the biparental geneticsystems have one evolutionarily stable strategy (ESS) and thearrhenotokous systems have another, but within each of thesecategories, all three ploidys have the same ESS. Where femalescan respond only to their own fecundities, their brood sex Tratiosdecline with increasing brood size, but their absolute investmentsin males increase; this response occurs even where the meanpatch size is very large and the mean sex ratio of parentalinvestment is therefore indistinguishable from one-half. Patternsof sex allocation in many kinds of spatially structured populationsmay depend critically on the ways in which females perceiveand respond to environmental features that predict the fitnessdistributions of their local mating aggregations.