Evolutionary Consequences of Sex-Specific Selection in Variable Environments: Four Simple Models Reveal Diverse Evolutionary Outcomes.

The evolutionary trajectories of species with separate sexes depend on the effects of genetic variation on female and male traits as well as the direction and alignment of selection between the sexes. Classical theory has shown that evolution is equally responsive to selection on females and males, with natural selection increasing the product of the average relative fitness of each sex over time. This simple rule underlies several important predictions regarding the maintenance of genetic variation, the genetic basis of adaptation, and the dynamics of "sexually antagonistic" alleles. Nevertheless, theories of sex-specific selection overwhelmingly focus on evolution in constant environments, and it remains unclear whether they apply under changing conditions. We derived four simple models of sex-specific selection in variable environments and explored how conditions of population subdivision, the timing of dispersal, sex differences in dispersal, and the nature of environmental change mediate the evolutionary dynamics of sex-specific adaptation. We find that these dynamics are acutely sensitive to ecological, demographic, and life-history attributes that vary widely among species, with classical predictions breaking down in contexts of environmental heterogeneity. The evolutionary rules governing sex-specific adaptation may therefore differ between species, suggesting new avenues for research on the evolution of sexual dimorphism.