Conflicts in natural selection constrain adaptation to climate change in Arabidopsis thaliana

Climate change has already caused noticeable changes in species-wide traits, such as the well-documented acceleration of spring flowering. Because the evolutionary past has favored certain combinations of traits, some strategies like fast growth with early flowering that are adaptive today are at odds with other plant resilience strategies such as elevated water use efficiency. We know that the evolution of trait combinations is shaped by genomic constraints, but it is unclear whether and how this is affected by natural selection from climate change. Growing hundreds of Arabidopsis thaliana natural populations under different rainfall regimes revealed opposing natural selection on flowering time and water use efficiency, with strong antagonistic genetic correlations and contrasting causal alleles identified by Genome-Wide Association analyses. Inactivation of the central flowering regulator FLC in multiple, diverse accessions relaxed trait correlations in a genetic background-dependent manner and allowed for the emergence of a novel adaptive trait combination--early flowering and intermediate water use efficiency. Future climates are predicted to escalate conflicts in natural selection among adaptive traits, but our work shows that surprisingly simple genetic changes can help solve these conflicts.