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The capacity for adaptation to climate warming in an annual plant (Brassica rapa)

The persistence of a declining population in the face of environmental change may depend on how fast natural selection restores fitness, a process called “evolutionary rescue”. In turn, evolutionary rescue depends on a population’s adaptive potential. Fisher’s theorem states that a population’s adaptive potential equals the additive genetic variance for fitness (VA(W)) divided by mean fitness . Both the numerator and denominator of this rate can differ across environments even when holding allele frequencies constant. However, little is known about how these rates change in wild populations during adaptation, including changes in additive and dominance variance. We assessed the change in adaptive potential and dominance variance in fitness (VD(W)) for a Québec population of wild mustard (Brassica rapa) under climate warming. We also assessed adaptive constraints that could arise from negative genetic correlations across environments. We grew a pedigreed population of 7000 plants under ambient and heated (+4°C) temperatures and estimated the change in , VA(W), VD(W), and the cross-environment genetic correlations (rA). As predicted, estimates of VA(W) and adaptive potentials were higher under heated conditions but non-significantly so. This is perhaps because, surprisingly, plants exposed to a warmer climate exhibited greater . Nevertheless, increased fitness in the warmer environment suggests a plasticity-based short-term potential for adaptation, and that weak but non-significant genetic correlations across environments will enable slow on-going adaptation to warming. Overall, this population of B. rapa harbours existing genetic architecture to persist under warmer temperatures through pre-adaptation but not through evolutionary rescue.