Rapid Evolutionary Responses of Field Mustard (Brassica rapa) under Experimental Drought

As climate change continues, plant populations are predicted to face more frequent and extreme drought events. Plants may respond to drought through evolution, plasticity, or both, and recent work has demonstrated that evolutionary responses may occur in just a few generations. However, anticipating how populations will respond to drought remains difficult. Prior work suggests that responses to drought may be anticipated at fitness and trait levels, but that underlying genetic mechanisms usually occur differently among populations and may sometimes lead to constraints. Brassica rapa (field mustard) presents a unique model to evaluate these evolutionary questions as it has been shown to adapt to natural drought through earlier flowering and drought escape, but the degree of parallel evolution to drought in natural populations is unclear. I combined several techniques including experimental evolution, the resurrection approach, pooled sequencing, and artificial selection to explore responses to drought in B. rapa. Specifically, I characterized how B. rapa responded to drought over just a few generations, assessed the consistency of evolutionary responses among replicates at phenotypic and genomic biological levels, and explored potential evolutionary constraints to drought adaptation that may result after rapid evolution. Using the abovementioned experimental approaches on this species allowed me to evaluate responses to drought absent confounding factors that the natural populations experienced and to assess the predictability of responses among multiple replicate populations under experimental environments. Broadly, elucidating responses to drought and their predictability in this system can help increase our understanding of how, and if, annual plants may respond to drought associated with changing climate