This finding suggests that plants that grow rapidly such as weeds may cope better with global warming than slower-growing plants such as redwood trees.
'Some species evolve fast enough to keep up with environmental change,' said Arthur Weis, UCI professor of ecology and evolutionary biology. 'Global warming may increase the pace of this change so that certain species may have difficulty keeping up. Plants with longer life cycles will have fewer generations over which to evolve.'
Weis and his team studied field mustard, a weedy plant found throughout the Northern Hemisphere.
In a greenhouse, they grew mustard plants at the same time from seeds collected near the UCI campus in the spring of 1997 - two years before a five-year drought - and seeds collected after the drought in the winter of 2004.
The plants were divided into three groups, each receiving different amounts of water mimicking precipitation patterns ranging from drought to very wet conditions. In all cases, the post-drought generation flowered earlier, regardless of the watering scheme.
This shift in genetic timing was further confirmed with an experiment that crossed the ancestors and descendents. As predicted, the intergenerational hybrids had an intermediate flowering time.
'Early winter rainfall did not change much during the drought, but the late winters and springs were unusually dry. This precipitation pattern put a selective pressure on plants to flower earlier, especially annual plants like field mustard,' Franks said. 'During drought, early bloomers complete seed production before the soil dries out, whereas late bloomers wither before they can seed.'
The technique of growing ancestors and descendents at the same time allowed the scientists to determine that the change in flower timing was in fact an evolutionary shift - not a simple reaction to changing weather conditions.
Today, Weis is the organizing chairman of Project Baseline, a national effort to collect and preserve seeds from contemporary plant populations. Decades from now, plant biologists will be able to resurrect these ancestral generations and compare them to their descendents.
'If we go out today and collect a large number of seeds and freeze them, they will be a resource available to the next generation of scientists,' Weis said. 'Because of global warming, the evolution explosion is already under way. If we act now, we'll have the tools necessary to determine in the future how species respond to climate change.'
This research was supported by the National Science Foundation. The study appears this week in the 'Proceedings of the National Academy of Sciences.'