The cold conditions of winter 2009-10 throughout the southern US offer a rare opportunity to assess the immediate biological impacts of extreme climate fluctuation. This project will document the effects of the extremely cold winter on Drosophila americana, a fly species native to North America and distributed over a broad latitudinal range. Previous studies of this species reveal polymorphisms in genes and traits that allow persistence in time of extreme temperatures, and these genotypes and phenotypes differentiate the extreme northern and southern populations. This study will assess genotypic and phenotypic variation in southern populations to test whether polymorphisms characteristic of northern populations have a higher prevalence immediately following an extremely cold winter.
Many features of the environment vary predictably in space and time, such as seasonal climate gradients in temperate regions. Organisms adapt to local conditions, yet day-to-day and year-to-year fluctuations occur as a consequence of weather systems. Genetic variation within species may play an important role in buffering populations against these fluctuations. This project will measure the immediate changes in the genetic and adaptive trait composition of populations following an extreme climatic event. The project will contribute to improved understanding of the capacity for genetic variation to buffer against climatic extremes, which is an important aspect of adaptation and persistence of species persistence as global climate and weather change.
The winter of 2009-10 was cold! By several climatological measures, record or near record low temperatures were experienced over the months of December, January and February throughout the southern US. We examined the hypothesis that geographically structured genetic variation buffers populations from this type of annual climate fluctuation. We used the fly species, Drosophila americana, that occurs throughout the central and eastern US to measure a shift in latitudinally distributed chromosomal variants and an associated overwintering response. Fly samples collected in the spring and summer of 2010 were compared to samples previously collected from the same locations. Frequencies of a derived chromosomal rearrangement characteristic of northern populations were higher, but not exceeding statistical thresholds, in 2010 compared to previous years in three of four samples from Alabama, Mississippi and Arkansas. Laboratory lines generated from flies collected from southern populations in 2010 were more responsive to overwintering cues of short daylength and cool temperature than lines collected in previous years, indicating a potential contribution to survival during extreme winter conditions. A similar comparison of new and old laboratory lines established from northern populations indicates the difference is unlikely caused by adaptation to laboratory culture. Ultimately, this project further characterized the variation that exists among populations and that can serve as a substrate for long-term evolutionary response to global climate change. This project provided training opportunities for two students that have gone on to respectively pursue an academic career in biology and a professional career in medicine. Two other students continuing to pursue advanced degrees also contributed to the project. A permanent collection of laboratory lines of D. americana was generated from the collection activities.
