Revisiting evolution at the rear edge

Antoine Perrier , Olivia Keenan, Laura Galloway

Rear-edge populations occur at species’ warmer range limits, with many still occupying glacial refugia. They offer valuable insights into evolution under changing climates yet are underused as models. From two decades of research, we identify three equally likely evolutionary patterns in rear edges: high levels of genetic diversity and differentiation, elevated genetic drift, and strong local adaptation. Multiple patterns create challenges for predicting the vulnerability, conservation value and adaptive potential of rear edges under future climates. Which factors drive these distinct outcomes, and why only some rear edges persist in former refugia, remains unclear. We propose avenues to address these gaps, leveraging rear edges as models to better understand evolution under climate change and improve predictions of species’ responses.