California got a bit more rain and snow this year thanks to El Niño, but is still suffering the effects of many years of drought. This drought is one example of the many extreme events, including storms and fires, that are increasing in frequency as the global climate continues to change. Not only does the drought in California affect the lives of millions of people, but it also has major impacts on many other living things.
While some species are declining or going extinct as a result of climatic changes, others may be able to adapt. Understanding how they do so is profoundly important for conservation. Furthermore, examining how climate change alters species gives us the opportunity to increase our understanding of the process of evolution, particularly when we can catch them in the act of evolving.
In an article my collaborators and I recently published in the journal Molecular Ecology, we examined how a drought that occurred in southern California between 1997 and 2004 influenced genetic changes in the plant Brassica rapa, also known as field mustard. Field mustard, a plant with bright yellow flowers, has been developed into a number of different crop varieties, including bok choy, rapini, and turnips, and also grows wild in California and throughout the U.S.
Our previous work showed that the drought favored plants that flowered earlier, which allowed them to escape the effects of late-season drought conditions. The populations evolved earlier flowering in just a few years. This was the first clear example of a rapid evolutionary change in a natural plant population in response to a change in climate.
In the new study, we examined genetic variation throughout the entire genome of the plant populations before and after the drought. We found many genetic changes in the populations. Some of the gene types that changed in frequency are linked to traits that would have been affected by the drought, such as flowering time and stress response. Also, two populations influenced by the same drought showed different genetic changes.
This research shows us that contrary to the previous belief that evolution is a very slow process, evolutionary changes can happen extremely rapidly. Thanks to recent advances in the technology of genetic sequencing, we can now watch genetic changes in populations as they evolve and adapt, as we did in this study. This approach opens up new windows onto evolution, showing us the details of this powerful and important process that constantly shapes life on earth. For any that doubt climate change or evolution, this study and many others provide key evidence of the reality and effects of these processes.
The field mustard plants in our study were able to rapidly adapt to climate change, and we could pinpoint the genetic changes that occurred that allowed this to happen. However, this does not mean that we don't need to worry about climate change because species will just evolve. The rapid pace of current climate change and reduced population sizes due to habitat loss and fragmentation means that many species will not be able to adapt fast enough. A recent analysis concluded that 1 in 6 species could face extinction if climate change continues unabated. To avoid this massive and irretrievable loss of biological diversity, we need to take concrete steps to reduce our environmental impact and use energy and resources in a more sustainable way.
When Charles Darwin first proposed the idea of evolution via natural selection, he knew that traits must be passed on from parents to offspring, but he had no idea how. Since then, we have discovered that traits are passed on through DNA, and we have learned to read this genetic code. New technology now allows us to obtain massive amounts of genetic information, and we can watch genetic changes in populations as they evolve in real time.
This detailed view of the process of evolution would have been beyond Darwin's wildest dreams, but is a reality today. Our study showed rapid evolution in a wild mustard plant, and provided a clear picture of the underlying genetic changes that occurred as these populations adapted to drought. This opens an exciting and dynamic view into evolution, and deepens our understanding of how life changes over time.