Maternal-zygotic gene conflict over sex determination: Effects of inbreeding

There is growing evidence that sex determination in a wide range of organis ms is determined by interactions between maternal-effect genes and zygotica lly expressing genes. Maternal-effect genes typically produce products (e.g ., mRNA or proteins) that are placed into the egg during oogenesis and ther efore depend upon maternal genotype. Here it is shown that maternal-effect and zygotic genes are subject to conflicting selective pressures over sex d etermination in species with partial inbreeding or subdivided populations. The optimal sex ratios for maternal-effect genes and zygotically expressing genes are derived for two models: partial inbreeding (sibmating) and subdi vided populations with local mating in temporary demes (focal, mate competi tion). In both cases, maternal-effect genes are selected to bias sex determ ination more toward females than are zygotically expressed genes. By invest igating the invasion criteria for zygotic genes in a population producing t he maternal optimum (and vice versa), it is shown that genetic conflict occ urs between these genes. Even relatively low levels of inbreeding or subdiv ision can result in maternal-zygotic gent: conflict over sex determination. The generality of maternal-zygotic gene conflict to sex determination evol ution is discussed; such conflict should be considered in genetic studies o f sex-determining mechanisms.