Selection in parental species predicts hybrid evolution

While hybridization is recognized as important in evolution, its contribution to adaptation and diversification remains poorly understood. Using genomically diverged island populations of the homoploid hybrid Italian sparrow, we test predictions for phenotypic trait values and evolvability based on patterns of parental species divergence in four plumage color traits. We find associations between parental divergence and trait evolution in Italian sparrows. Fixed major QTL in species differences lead to hybrids with higher trait variation, and hence evolvability, than the parent species. Back and crown plumage show no correlation between current within-parent variability and among-parent differentiation. For these traits, Italian sparrow phenotypes are biased towards axes of high parental differentiation and show greater phenotypic novelty along axes of low current parental evolvability, as predicted when major QTL are involved in species differences. Crown color has consistently evolved back towards one parent, while back color varies among islands. We also find significant among-population diversification within the Italian sparrow. Hence, hybridization of the same parent species can generate different phenotypes. In conclusion, we find support for parental phenotypic divergence patterns reflecting divergence mechanisms, and hence such patterns can be useful in predicting how hybridization alters the potential to evolve and adapt.