Spatial selection and local adaptation jointly shape life-history evolution during range expansion
In the context of climate change and species invasions, range shifts increasingly gain attention because the rates at which they occur in the Anthropocene induce fast shifts in biological assemblages. During such range shifts, species experience multiple selection pressures. Especially for poleward expansions, a straightforward interpretation of the observed evolutionary dynamics is hampered because of the joint action of evolutionary processes related to spatial selection and to adaptation towards local climatic conditions. To disentangle the effects of these two processes, we integrated stochastic modeling and empirical approaches, using the spider mite Tetranychus urticae as a model species. We demonstrate considerable latitudinal quantitative genetic divergence in life-history traits in T. urticae, that was shaped by both spatial selection and local adaptation. The former mainly affected dispersal behavior, while development was mainly shaped by adaptation to the local climate. Divergence in life-history traits in species shifting their range poleward can consequently be jointly determined by fast local adaptation to the environmental gradient and contemporary evolutionary dynamics resulting from spatial selection. The integration of modeling with common garden experiments provides a powerful tool to study the contribution of these two evolutionary processes on life-history evolution during range expansion.