Adaptive introgression in the context of climate adaptation

Thibault Leroy , Myriam Heuertz

As the biosphere faces accelerating environmental disruption, including climate change, and the prospect of an anthropogenically-driven mass extinction, understanding the mechanisms that enable species to adapt has become increasingly urgent. One mechanism attracting growing attention is adaptive introgression, the transfer of beneficial genetic variation between closely related species. Although frequently invoked as a potential driver of adaptation to rapid environmental change, including climate change, its overall importance remains debated. In this review we take a balanced and evidence-based perspective. After introducing approaches for identifying potential donor and recipient species of introgression events, we review both the classical methods for detecting introgression and selection, and the recent methodological advances that allow their joint inference. To date, we have identified roughly twenty published studies that provide at least partial support for a connection between introgression and climate-related adaptation, most often involving adaptation to climatic oscillations during the late Pleistocene rather than to contemporary climate adaptation. Although adaptive introgression is frequently invoked in evolutionary and conservation biology, we highlight a persistent gap between its theoretical expectation and the scarcity of well-documented, functionally or ecologically validated examples. Considering the pressing challenges to preserve biodiversity and improve predictions of adaptive potentials under climate change, addressing this gap is of paramount importance. We conclude by proposing key research directions of research at the intersection of macroevolution, microevolution, and the evolutionary ecology of communities.