Species that exist in heterogeneous environments experience selection for specialization that is opposed by the homogenizing forces of migration and recombination. Migration tends to reduce associations between alleles and habitats, whereas recombination tends to break down associations among loci. The idea that heterogeneity should favor the evolution of isolating mechanisms has motivated evolutionary studies of reduced migration, habitat preference, and assortative mating. However, costly female choice of high-quality males can also evolve in heterogeneous populations and is not hindered by either recombination or migration. When information on male fitness is available through indicator traits, female choice based on these traits increases associations between female choice alleles and locally adapted alleles. Not only does female choice evolve in a heterogeneous environment, it acts to enhance the level of genetic variation and is thus self-reinforcing. The amount of female choice at equilibrium depends on how well mixed the habitats are, how much information on male genotype is available, and how different the habitats are. Female choice reaches the highest levels for intermediate levels of heterogeneity, because at such levels of heterogeneity there is both a high risk and high cost of mismating.
Corresponding Editor: M. Whitlock