The capacity for adaptation to climate warming in wild mustard (Brassica rapa)

Background/Question/Methods

The persistence of a population declining due to environmental change can depend on how quickly natural selection restores fitness, a process called “evolutionary rescue”. In turn, evolutionary rescue depends on the genetic variation in adaptive potential. Fisher’s theorem states that the rate of adaptation equals the additive genetic variance for fitness (VA(W)) divided by mean fitness (W¯). But both the numerator and denominator of this rate can differ across environments, even when holding allele frequencies constant. We assessed the change in adaptive potential for a Québec population of wild mustard (Brassica rapa) under climate warming. We grew a pedigreed population of 7000 plants under ambient and manipulated (+4°C) temperatures and estimated W¯ and VA(W) with the animal model. We also estimated genetic correlations within traits and across environments to assess adaptive constraints.

Results/Conclusions

Surprisingly, plants exposed to a warmer climate exhibited greater W‾. Estimates of VA(W) were near 0, but insignificantly higher under warmer conditions. Genetic correlations across environments were insignificant. Our findings suggest that adaptive potentials are low under ambient conditions and possibly higher under heated conditions. Nevertheless, increased mean fitness in the warmer environment suggests pre-adaptation by phenotypic plasticity. Weak genetic correlations across environments will also enable slow, but on-going adaptation to warmer climates interceded with variable temperatures. Overall, our findings show that B. rapa harbours existing genetic potential to persist under warmer temperatures through plasticity.