Sexually antagonistic environments and the stability of environmental sex determination

Just as sexually antagonistic genetic variants have different effects on male and female fitness, environmental conditions too can have sexually antagonistic fitness effects. Such Charnov-Bull effects have been invoked to explain the origin and persistence of environmental sex determination (ESD), which allows development of each sex in the environments in which it has a comparative advantage. Here, we study different forms of Charnov-Bull effects to characterize how they shape the evolution and stability of ESD. We show that the precise functional form of Charnov-Bull effects can generate large differences in the vulnerability of ESD systems to the invasion of sex-biasing alleles, as well as in the fate of those alleles if they invade. For some configurations of Charnov-Bull effects, strong sex-biasing alleles are likely to spread to intermediate frequencies, rather than to fixation, resulting in mixed ESD systems in which large genetic effects segregate. Overall, our results indicate that the precise nature of Charnov-Bull effects can play a crucial role in the evolutionary dynamics of ESD.