Meeting Abstract
Experimental evolution uses replicated, populations that generally evolve along similar trajectories, but can diverge over time. We selected for starvation resistance in 3 populations (S) of Drosophila melanogaster. After ~100 generations of selection, S populations survived >11 days without food, whereas fed control (F) flies survived less than 4 days. One S replicate consistently survived >24 hours longer than the other populations, and genomic data revealed significant divergence in SNP allele frequencies across the genome. To identify the mechanisms underlying these differences, we analyzed energy budgets of S and F flies. Starvation survival can be increased by three non-exclusive physiological mechanisms. S flies can store more energy before selection is imposed, they can use energy less rapidly, or they can tolerate lower energy contents (i.e. utilize a greater proportion of initial energy stores before dying). Flies may also ingest microbes that have colonized corpses of flies who have already died (“cannibalism”), or acquire energy from fecal material (coprophagy). S flies stored 3-4 times more lipid than controls. Their metabolic rates were ~25% lower, but they did not consume a greater fraction of initial lipid before death. Both S and F flies survived longer in vials containing fly corpses, but selected flies were not “better” cannibals. The presence of large quantities of fecal material did not affect survival. In all assays, replicate populations did not differ significantly. We conclude that population divergence in starvation survival is likely the result of relatively small changes in lipid storage and metabolic rate that were statistically undetectable, but together have a significant effect on starvation resistance. Supported by IOS-1355210 from NSF and R15-GM100395 from NIGMS.
