Résumé
Conventional wisdom predicts that sequential founder events will cause
genetic diversity to erode in species with expanding geographic ranges,
limiting evolutionary potential at the range margin. Here, we show that
invasive European starlings (Sturnus vulgaris) in South Africa preserve
genetic diversity during range expansion, possibly as a result of frequent
long-distance dispersal events. We further show that unfavourable
environmental conditions trigger enhanced dispersal, as indicated by
signatures of selection detected across the expanding range. This brings
genetic variation to the expansion front, counterbalancing the cumulative
effects of sequential founding events and optimizing standing genetic
diversity and thus evolutionary potential at range margins during spread.
Therefore, dispersal strategies should be highlighted as key determinants
of the ecological and evolutionary performances of species in novel
environments and in response to global environmental change.