Complex effects of assortative mating on adaptation to environmental change in the presence of sex-specific selection

Previous theory suggests that fast adaptation of body size and phenology to climate warming could be facilitated by assortative mating. We here test whether this still holds when natural selection is sex-specific and assortative mating is driven by different mechanisms. We model a trait with identical distribution for females and males, but different optima across sexes and time. Predictions derived from the infinitesimal model of inheritance are confirmed by individual-based simulations. We find that female maladaptation depends on a sexual-conflict mismatch in a constant environment, and an adaptive lag generated by the environmental change. By strengthening the effect of natural selection on females, assortative mating reduces the sexual-conflict mismatch compared to random mating. However, it can either increase or decrease the adaptive lag, depending on the relative strength of natural selection on females versus males. Conditions under which assortative mating is beneficial depend on whether the environmental change and the sexual conflict displace the mean phenotype in the same direction, the strength of the sexual conflict and the assortment, and the mechanism that drives assortative mating. Associated with sex-specific selection, assortative mating does not always facilitate adaptation to environmental change, and its effects depend on how it is modeled.