Résumé
Genomic offset metrics are increasingly used to predict population
maladaptation under changing climates, based on the assumption of a
negative statistical relationship between offset measures and local
relative fitness. Recent theoretical advances have confirmed this
relationship by relating genomic offset to phenotypic trait distances
along selection gradients. However, these metrics typically rely on the
assumption that stabilizing selection, which maintains local adaptive
optima, operates on fitness-related traits through Gaussian-shaped
selection gradients. In this study, we extend the theory to accommodate
more diverse forms of selection gradients and introduce more general
genomic offset measures that preserve the fitness-offset relationship. We
validate this generalization through simulations and demonstrate the
utility of these new measures in predicting relative fitness in common
garden experiments involving three plant species: pearl millet, a vital
staple cereal grown in arid soils, and two emblematic North American tree
species, balsam poplar and red spruce. Our findings indicate that assuming
a local Gaussian-shaped selection gradient for climate adaptation is a
robust approximation for these species. These results have important
implications for validating genomic offset predictions using fitness
proxies and for studies that aim to predict fitness loss based on genomic
offset metrics.