The capacity for adaptation to climate warming in a naturalized annual plant ( <i>Brassica rapa</i> )

The persistence of a declining population under 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 capacity, which can be defined as the ratio between additive genetic variance for fitness [VA(W)] and mean fitness ($\bar W$), or represented by ${\Delta _{\textit{evol}}}\bar W$. However, little is known about how both VA(W) and $\bar W$ change in wild populations during environmental change, including changes in dominance variance for fitness [VD(W)]. We assessed the change in ${\Delta _{\textit{evol}}}\bar W$ and 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 for fitness across environments. We grew a pedigreed population of 7,000 plants under ambient and heated (+4 °C) temperatures and estimated the change in mean survival and fecundity ($\bar W$), VA(W), and VD(W), plus cross-environment genetic correlations (rA). VA for fecundity non-significantly increased under heated conditions, mean fecundity ($\bar W$) increased significantly, and ${\Delta _{\textit{evol}}}\bar W$ was unchanged. We also detected no significant rA for survival and fecundity, suggesting little antagonistic constraint to adaptation. Overall, while this B. rapa population may feature some adaptive plasticity via fecundity, its adaptive capacity to warming seems limited.