Prospective and Retrospective Studies on Plant Evolutionary Response to Climate Change

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Canada’s last episode of climate warming, following the Pleistocene, played out across millennia. Species had many generations for evolutionary re-adjustment to northern latitudes as they emerged from glacial refugia in the south. Current climate change is occurring over decades, and some species will persist only through rapid evolutionary response to abrupt changes in conditions. It is crucial that practical decisions on preservation of biodiversity and ecosystem services be informed by basic evidence on evolutionary potential. Test cases exploring limits on adaptive evolution set by genetic variance, and efficacy of conservation measures to relive those limits, are needed. We will explore 3 themes related to evolutionary limits, giving training opportunities for 5 graduate students and over 30 undergraduates - HQP for the generation that will make those decisions. Theme 1. Phenological divergence, gene flow and constraint. Some suggest that depressed genetic variance can be enhanced by Assisted Gene Flow (AGF)—translocate southern migrants (genetically adapted to thermal stress) into declining northern populations. Simple in concept, practical issues can complicate AGF implementation. We will do experiments to mimic initial stages of AGF to resolve issues arising from flowering time divergence between the declining resident population and the ‘rescuing’ migrants. One project field-tests quantitative methods to estimate resident-migrant hybridization rates from overlap in flowering schedules. Another examines difficulties of introgressing thermal tolerance from southern migrants into a northern population arising from the inherent linkage disequilibrium across space of tolerance and reproductive timing. Finally, a third project examines the consequences of pleiotropy between flowering time and pollen quality, prompted by recent discoveries in my lab. Theme 2. Mean fitness and the additive genetic variance in fitness, in the context of ‘evolutionary rescue’. The probability of ‘rescue’ from climate change increases if evolutionary response can restore a mean absolute fitness to >1. Environmental shift will lower mean fitness. What will happen to the additive genetic variance in fitness? At what point might it fall so low as to prevent a sufficient evolutionary response? Seed/seedling survival and seed production will be evaluated in pedigreed populations of Brassica rapa under historically typical and novel conditions. A new extension of aster analysis will estimate variance components of the breeding value for fitness. Theme 3. The resurrection approach measures phenotypic evolution. The most direct test for phenotypic evolution is by growing ancestral and descendent generations in a common environment. We will make first use of the Project Baseline seed archive to perform resurrection experiments to detect evolution in progress as climate change proceeds.