Sex-ratio selection with asymmetrical migration of the sexes can lead to an uneven sex ratio

Because asymmetrical migration of the sexes generates local biases in sex-ratio it has been suggested that the evolution of locally adapted uneven sex-ratios is favoured as far as this condition is concerned. Recent theoretical models, however, challenged this hypothesis. This suggestion has been re-examined by means of a model that assumes (1) population subdivision into two effectively infinite subpopulations, (2) one motile sex with restricted migration between subpopulations and (3) environmental sex determination based on subpopulation size. It is shown that selection leads to an evolutionary stable uneven sex-ratio with realistic assumptions concerning spatial and temporal heterogeneity of subpopulation sizes.