Biology

Dr. Subhash Rajpurohit
Department of Biology, University of Pennsylvania, Philadelphia, USA

In natural populations of the genetic model, Drosophila melanogaster, latitudinal clines have been widely observed. These patterns are commonly interpreted as evidence of natural selection and local adaptation, but the mechanisms and evolutionary dynamics that generate and maintain clines are largely unresolved. Many of the same environmental parameters that vary with latitude also vary predictably over seasonal time, allowing for a mechanistic dissection of rapid evolution in a genetic model. In temperate habitats, fly populations fluctuate seasonally, reaching peak abundance in late summer followed by a pronounced crash in fall. Prior work has demonstrated that these populations experience rapid adaptive responses to seasonality in replicate years. This occurs over approximately 10-15 generations (spring to autumn), and results in 1) a genomic signature of seasonal adaptation in which a nonrandom set of molecular variants cycle in frequency with season, and 2) predictable change in life histories and fitness associated traits. In order to further address fundamental dynamics of rapid, seasonal adaptation, we performed field based experimental evolution studies over three successive years. Our data demonstrate that natural Drosophila populations respond rapidly (within three generations) and predictably to specific environmental parameters in the field, and that the shifting selection regimes associated with distinct seasonal environments appears to maintain genetic and phenotypic variation in natural populations.