‘What’s better for adaptation – recycling old genetic variants or taking advantage of new (epi)mutations?’
My group is addressing fundamental questions in evolutionary biology, using both genome-first and phenotype-first approaches: (i) Where do new genetic variants come from? (ii) Why are some variants maintained for a much longer time than others? (iii) And why are some combinations of variants incompatible with each other?
The background for these questions is our population genomic work in Arabidopsis and the related genus Capsella. In collaboration with our colleagues (Bergelson, Ecker, Mott, Nordborg, K. Schmid and others), and with the help of Monsanto, we have been describing whole-genome variation in wild isolates of A. thaliana (http://1001genomes.org), and in Capsella, where two species have gone through recent extreme genetic bottlenecks (with Neuffer, Slotte & Wright labs). A remarkable finding that has emerged from the Capsella work is the ubiquity of long-term balancing selection, specifically at immunity loci.
On the other end of the spectrum, we are analyzing new DNA mutations and epigenetic variants that have arisen under laboratory conditions or in a natural mutation accumulation experiment. The latter studies take advantage of an A. thaliana lineage that was apparently introduced to North America in historic times and accounts for about half the population there (with Bergelson and Burbano labs). We have been able to support what we see in the extant North American population by whole-genome sequencing of herbarium samples from the 19th century.
The ultimate goal of our top-down studies is to understand how genetic and epigenetic variation interacts with reassortment of variants after crosses and with natural selection to shape geographic patterns of diversity. To this end, we are following natural populations during the season and over consecutive years. This work in turn is complemented by forward genetic analyses, especially of detrimental combinations of immune receptors that evolved in separate lineages (with Dangl lab). This particular area of our work nicely dovetails with the Capsella whole-genome inferences on maintenance of very old immunity alleles, and it is revealing new mechanistic insights into the function of the plant immune system.
Additional information about our work can be found on our website, http://weigelworld.org.