View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

Genetic correlations between traits are thought to be a main constraint to adaptation, as multiple advantageous trait strategies cannot evolve simultaneously. However, comprehensive studies of how genetic correlations persist in natural populations and their ecological relevance when subject to climate-driven natural selection are rare. Through common garden experiments with Arabidopsis thaliana, Exposito-Alonso et al. (2019) showed pervasive antagonistic selection between high and low rainfall environments. Mining and extending the Arapheno database for published ecologically-relevant traits, we quantify direct and total phenotypic selection (Arnold & Lande 1983) under these drought and non-drought environments. We find evidence that the observed antagonistic selection can be explained by a phenotypic trade-off of mutually-exclusive ecological strategies to climate stressors; commonly referred to as drought escape and drought avoidance (Ludlow 1989). In the low precipitation environment, strong total selection favored phenotypes relating to escaping drought by flowering early at the expense of low water use efficiency, a strategy persistent in the warm edge of the species’ range, as it reduces mortality. However, when we control for multiple correlated traits related to escape and drought avoidance, we identified a direct positive selection over highwater-use efficiency, which is typically associated with late flowering ecotypes. This reversion in selection highlights that there must be a fitness trade-off between the two strategies. Genome-wide association approaches allowed us to confirm these traits are genetically correlated and, importantly, that hotspots of genetic correlation across these phenotypes map to corresponding regions of the genome that are under antagonistic selection. These results indicate that natural populations of A. thaliana experience a genetic constraint to drought adaptation and importantly, this should be accounted for when making predictions about how species will adapt to a changing climate.

Genetic constraint of complex traits for drought adaptation in Arabidopsis