The Demographic Costs of Sexually Antagonistic Selection in Partially Selfing Populations

When selection differs between the sexes, genes expressed by both males and females can experience sexually antagonistic (SA) selection, where beneficial alleles for one sex are deleterious for the other. Classic population genetics theory has been fundamental to understanding how and when SA genetic variation can be maintained by balancing selection, but these models have rarely considered the demographic consequences of coexisting alleles with deleterious fitness effects in each sex. In this article, we develop a stage-structured Mendelian matrix model and jointly analyze the evolutionary and demographic consequences of SA selection in obligately outcrossing (i.e., dioecious/gonochorous) and partially selfing hermaphrodite populations. We focus on identifying when SA polymorphisms are maintained by balancing selection and the population growth rate remains positive. Additionally, we analyze the effects of inbreeding depression manifesting at different life history stages and give an illustrative example of the potential for SA polymorphism in real populations using empirically estimated demographic rates for the hermaphroditic flowering plant Mimulus guttatus. Our results show that when population intrinsic growth rates approach 1, extinction occurs across large swathes of parameter space, favoring SA polymorphism or the fixation of male-beneficial alleles, and that inbreeding depression is a significant problem for maintaining SA polymorphism in partially selfing populations. Despite these demographic challenges, our example with M. guttatus appears to show that demographic rates observed in some real populations can sustain large regions of viable SA polymorphic space.