116 Rethinking Resilience: Testing Tolerance in Drosophila

Faculty Mentor: Sophie Caron (School of Biological Sciences, University of Utah)

Individual species respond to climate change in various manners, but it is unknown whether species adapted to harsher environments are more resistant to stress. To address this question, I compared species’ tolerances to food and water deprivation, ethanol, and heat. I compared the resistance of Drosophila pseudoobscura and Drosophila persimilis — evolutionarily similar species living in the mountains of the American West (Dobzhansky & Carl, 1946) — to that of Drosophila melanogaster and Drosophila simulans— evolutionarily similar cosmopolitan species that have evolved as human commensals (Matute & Ayroles, 2014). I hypothesized that D. pseudoobscura and D. persimilis have higher resistance to stress because they have adapted to survive the harsh climate of the American West, where food and water sources are scarce in comparison to a human environment.

Climate change increases heat waves, droughts, and extreme precipitation (IPCC, 2019), which lowers food source availability. To determine resistance to food and water deprivation, I performed a series of starvation and desiccation assays. When flies were deprived of food and water, D. simulans and D. melanogaster died quicker while D. pseudoobscura and D. persimilis died slower. When flies were deprived of water only, unexpectedly, D. melanogaster was the most tolerant species. In addition to decreased food availability, climate change yields higher temperatures, which lower fermentation time (Youcai & Ran, 2021). Consequently, flies and ethanol, a fermented product, interactions increase. I performed ethanol resistance and recovery assays. Initial ethanol resistance was the highest in D. pseudoobscura and D.  persimilis. However, after four hours of recovery, only D. melanogaster fully recovered. As aforementioned, increased temperatures are a direct trademark of climate change. To determine resistance to heat, I exposed the species to four different temperatures (30° C, 35° C, 37° C, 42° C) and measured their recovery. Preliminary results suggest Drosophila pseudoobscura and Drosophila persimilis have a lower heat tolerance than Drosophila melanogaster and Drosophila simulans.

D. pseudoobscura and D. persimilis had higher resistance to food and water depravation and initial ethanol exposure, partially supporting my hypothesis that they are more resistant to stress. In most conditions, sister species followed the similar patterns, suggesting that evolutionary history and ecology may indicate species’ resilience to climate change. In future experiments, I will test resistance to other stressors including atmospheric pressure and UV tolerance. Determining tolerance against environmental stresses demonstrates how climate change affects different species and elucidates unique evolutionary traits of individual species.