Reduced climate adaptation at range edges in North American Arabidopsis lyrata

Aim Species' range limits, when not caused by dispersal limitation, are the result of constraints to the evolution of the ecological niche such that further range expansion is slow or not possible. An important evolutionary constraint at range edges may be the enhanced action of genetic drift. Here we tested whether a history of small population size and enhanced genetic drift was linked with reduced adaptation at range limits. Location Eastern North America. Time period 2017-2019. Taxon Arabidopsis lyrata subsp. lyrata. Methods We performed a latitudinal transplant experiment with sites across and beyond the species' distribution of North American Arabidopsis lyrata. Plants originated from the centre and the periphery, and the latter shared a history of range expansion or long-term isolation and had low genetic diversity. We tested for adaptation by considering climatic variables that had previously been associated with both niche and range limits. Results Multiplicative performance of plants was lower the more different the temperature regime between a transplant site and a home site was, supporting climate adaptation. However, populations performed worse only when conditions were warmer at the transplant sites and better when conditions were colder, indicating that despite divergent adaptation to climate, the species seems to prefer living in cooler areas than where it is found currently. Finally, populations with low genetic diversity had a lower performance under a climate similar to that of their home sites, and performance declined more strongly under warmer conditions. Main conclusions Our study provides evidence that genetic drift reduces adaptation at species' range limits, and that populations with a history of genetic drift are especially vulnerable under global warming.