1. Evolutionary response to climate change

Evolution of time to first flowering.

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.

Representative publication:

Franks, S.J., S. Sim and A. Weis. 2007. Rapid evolution of flowering time by an annual plant in response to a climate fluctuation. Proceedings of the National Academy of Sciences 104(4): 1278-1282

2. Phenological assortative mating

Early tends to mate with early, and late with late.

Variation in flowering time induces phenological assortative mating (early bloomers tend to mate with other early bloomers while late mates with late) 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 Brassica rapa.

Representative publication:

Weis, A. and T. Kossler. 2004. Genetic variation in flowering time induces phenological assortative mating: Quantitative genetic methods applied to Brassica rapa. American Journal of Botany 91(6): 825-836

3. Plant tolerance to herbivory

Although a few plant species recover completely from seemingly devastating herbivore attack, most do not. We are using an artificial evolution protocol to see if the evolution of improved tolerance comes at the expense of reduced general growth performance. This work is in colaboration with Dr. Ellen Simms at the University of California Berkeley.