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Jason Weir


PhD, University of British Columbia
PostDoc, University of Chicago

SW 549A
SW 544


1) Evolutionary Response to Climate Change: Global warming will change the growing season in many parts of the world. In temperate areas frosts will stop sooner in spring and start later in fall. In arid areas, growing season will contract with drought. These changes in the seasonal rhythms will alter the selective regimes acting on the genes that control when, and for how long, plants come into flower.

When the shift from vegetative growth to reproduction occurs too early, plants have few resources to make progeny. When the shift is too late they do not have enough time to mature their progeny. My lab is investigating this trade-off using field mustard, Brassica rapa, a winter annual.

Recent decreases in spring precipitation in California have abbreviated B. rapa‘s growing season. My lab has detected a rapid evolutionary shift towards earlier flowering in California populations using a protocol we call the “resurrection paradigm.” Seeds collected in 1997 (before drought) and held in cold storage were revived and grown side-by-side with seeds collected from the same populations in 2004 (after 7 years of drought). Given the same environmental conditions, the post-drought generation flowered 16% sooner than the pre-drought.

My current plans are to collect, dry and freeze seeds from several well-chosen plant species. As global warming proceeds, these ‘ancestral’ seeds can be resurrected and grown beside their ‘descendents’ to monitor the rate of evolutionary change in a variety of functional characters.

2) Phenological Assortative Mating: Variation in flowering time induces phenological assortative mating (early bloomers tend to mate with other early bloomers while late mates with latee) and this has interesting consequences for short-term evolution. The genetic variance for flowering time will be inflated by assortative mating, and this may accelerate its response to natural selection. I have a number of experiments underway to evaluate the degree of genetic variance inflation in B. rapa.