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. Fixed major QTL in species differences, favoured by strong selection, are expected to lead to hybrids with higher evolvability than the parent species. We find associations between parental divergence and trait evolution in Italian sparrows. Rump color shows little evidence of major QTL, and hybrid evolution closely matches parental variability. Back and crown plumage, however, show evidence of major QTL in species differences. 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 among-island diversification within the Italian sparrow. Hence, hybridization of the same parent species can generate different phenotypes. In conclusion, we find that parental phenotypic divergence patterns can be useful in predicting hybrid evolutionary potential.