Sex-specific dispersal in spatially varying environments leads to habitat-dependent evolutionarily stable offspring sex ratios

Abstract

When the environment varies spatially, so that some habitats are more favorable to reproduction than others, an individual should attempt to increase the number of offspring establishing in high-quality habitats. Hence, if male and female dispersal behavior differ, it may be adaptive to produce more offspring of the more dispersing sex in low-quality habitats, since these offspring are likely to disperse to another patch, and more offspring of the most philopatric sex in high-quality habitats, since these offspring are likely to remain in that patch. Such a strategy is shown to be evolutionarily stable provided that male and female dispersal rates are different and that reproductive success varies between habitats (lack of ideal free distribution). Highly biased sex ratios are predicted (1) in rare habitats, (2) in poor habitats, (3) when difference between habitat quality is large, (4) when at least one sex disperses at a rate close to random with respect to habitat availability, (5) when both sexes disperse at a high rate, (6) when individuals are unable to select their reproducing habitat, and, presumably, (7) with moderate temporal variation of habitat quality. The model appears to be a good candidate to explain the pattern of sex ratio variation in a variety of species: phytophagous arthropods, species with environmental sex determination, and territorial passerines.