Tracking adaptation to seasonal insecticide pressure in Drosophila
Authors: Marianthi Karageorgi 1; Mark C. Bitter 1; Caitlynn To-Duyen Tran 1; Caileb Travier 1; Hayes Oken 2; Skyler Berardi 2; Paul Schmidt 2; Dmitri A. Petrov 1
Affiliations: 1) Stanford University; 2) University of Pennsylvania
Keywords: Ecological & conservation genetics
Understanding how organisms adapt to chemical pressures (e.g., plant allelochemicals and insecticides) is a central theme in evolutionary ecology. Adaptation to chemical pressures over ecological timescales provides an excellent study system to address the question because adaptation can be directly observed. In this project, we track the pace and the underlying phenotypic and genomic architecture of adaptation to seasonal insecticide exposure in replicate populations of Drosophila melanogaster in a field mesocosm experiment. The experiment lasted from early summer to late fall, and we performed high resolution temporal sampling to track evolution of insecticide resistance, other fitness-associated phenotypes, and allele frequencies genome-wide. We found that high insecticide resistance rapidly evolved in parallel in replicate populations of D. melanogaster following insecticide exposure in summer; when pesticide application ceased, resistance steadily declined until winter. The observed decline in resistance is consistent with known fitness costs of resistance in the absence of insecticide exposure. We also determined whether the evolution of insecticide resistance interacted with the evolution of other seasonal fitness-associated phenotypes, allowing us characterize trade-offs between adaptation to insecticide exposure and adaptation to seasonality. Last, the genomic data allowed test for the contribution of known insecticide resistance genes to the observed patterns in an unbiased, genome-wide manner. Overall, we expect that our study will provide insights into the phenotypic and genotypic architecture underlying rapid adaptation to chemical pressures.