3 years ago

Adaptive evolution under extreme genetic drift in oxidatively stressed Caenorhabditis elegans.

Suzanne Estes, Dana K Howe, Michael J Lue, Stephen F Christy, Dee R Denver, Griselda Velasco, Riana I Wernick
A mutation-accumulation (MA) experiment with Caenorhabditis elegans nematodes was conducted in which replicate, independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain mutant, gas-1 . The original intent of the study was to assess the effect of ETC dysfunction involving elevated reactive oxygen species (ROS) production on patterns of spontaneous germline mutation. In contrast to results of standard MA experiments, gas-1 MA lines evolved slightly higher mean fitness alongside reduced among-line genetic variance compared to their ancestor. Likewise, the gas-1 MA lines experienced partial recovery to wildtype ROS levels. Whole-genome sequencing and analysis revealed that the molecular spectrum but not the overall rate of nuclear DNA mutation differed from wildtype patterns. Further analysis revealed an enrichment of mutations in loci that occur in a gas-1 -centric region of the C. elegans interactome, and could be classified into a small number of functional-genomic categories. Characterization of a backcrossed four-mutation set isolated from one gas-1 MA line revealed this combination to be beneficial on both gas-1 mutant and wildtype genetic backgrounds. Our combined results suggest that selection favouring beneficial mutations can be powerful even under unfavourable population genetic conditions, and agree with fitness landscape theory predicting an inverse relationship between population fitness and the likelihood of adaptation.

Publisher URL: http://doi.org/10.1093/gbe/evx222

DOI: 10.1093/gbe/evx222

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