Invasion and maintenance of alleles that influence mating and parental success.

Here we develop a model of the invasion, polymorphism, fixation and extinction analysis of genes that differentially influence the mating and parenting success of the two sexes. The model could have application, for example, to the maintenance of homosexuality in diploid populations. The analysis focuses on systems in which mating success is density-dependent and contrasts the results with the density-independent case. Five situations are analyzed, including cases where male and female parenting success is affected in the same and in different directions by the alleles in question. As part of the analysis, a technique is outlined for identifying boundaries between regions where polymorphisms occur and regions where the alleles under consideration go either to fixation or extinction. The results indicate that, unlike in the density-independent case, in the density-dependent case the degree of dominance of the types of alleles analyzed here critically determines whether such alleles are able to invade a population, exist as a polymorphism, or go to fixation.