Format: ORAL

Antoine Perrier1 Laura F. Galloway1

1 Department of Biology, University of Virginia, Charlottesville VA, USA

How past evolutionary dynamics have shaped range limits remains a central and timely question in ecology and evolutionary research, especially when predicting how species ranges will respond to future climates. The rear edge – remnant populations persisting in former glacial refugia – is particularly exposed to climate change as these populations often occur at the warmer range limits. However, rear-edge populations may have served as distinct genetic diversity reservoirs during glaciation periods, providing beneficial variation to adapt to warming post-glacial climates, and increasing their ability to persist under future climates. We assessed climate adaptation at the rear edge of the herb Campanula americana. Rear-edge populations of this species are likely glacial relicts, genetically distinct from the rest of the range, and nowadays occur in distinct and marginal habits. These populations also show great phenotypic differentiation from the rest of the range linked to adaptation to the warmer rear-edge climates, through delayed flowering phenology and reduced vernalization requirements. Here we tested whether this distinctiveness also translates into differences in local adaptation, by raising populations from the core and the rear edge in three common garden experiments. We found that populations across the range were generally locally adapted, but it was much stronger in the rear-edge site. There rear-edge populations exhibited much higher fitness than more northern populations, which experienced a lack of reproduction due to low vernalization conditions. Rear-edge populations may thus show greater resilience under future warmer winters due to their reduced vernalization requirements, while core populations may be strongly negatively affected.