Rapid evolution in response to climate-change-induced drought and its demographic and genetic controls

Populations often vary in their evolutionary responses to a shared environmental perturbation. A key hurdle in building more predictive models of rapid evolution is understanding this variation – why do some populations and traits evolve while others do not? However, studies documenting rapid evolution usually lack the demographic and genetic data needed to understand varied evolutionary responses. We combined long-term demographic and environmental data, estimates of quantitative genetic variance components, and a resurrection experiment to gain mechanistic insights into variation in evolutionary responses of five traits in two populations of a California endemic plant that recently experienced a severe multiyear drought. Earlier flowering phenology evolved in only one of the two populations, though both populations experienced similar precipitation patterns and demographic declines during drought and were estimated to have similar narrow-sense heritability of flowering phenology. However, demographic data indicated that seed input in years prior to the drought was 125% higher in the non-evolving population compared to the evolving population, suggesting that recruitment from the seedbank may have constrained evolution in the non-evolving population. Gene flow through time via seed banks may be an important, underappreciated control on rapid evolution in response to extreme environmental perturbations.