Sex and Mitonuclear Adaptation in Experimental Populations.

To reveal phenotypic and functional genomic patterns of mitonuclear adaptation, a laboratory adaptation study with nematodes was conducted in which independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain (ETC) mutant, Following 60 generations of evolution in large population sizes with competition for food resources, two distinct classes of lines representing different degrees of adaptive response emerged: a low-fitness class that exhibited minimal or no improvement compared to the mutant ancestor, and a high-fitness class containing lines that exhibited partial recovery of wild-type fitness. Many lines that achieved higher reproductive and competitive fitness levels were also noted to evolve high frequencies of males during the experiment, consistent with adaptation in these lines having been facilitated by outcrossing. Whole-genome sequencing and analysis revealed an enrichment of mutations in loci that occur in a -centric region of the interactome and could be classified into a small number of functional genomic categories.

Adaptive Evolution under Extreme Genetic Drift in Oxidatively Stressed Caenorhabditis elegans.

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 electron transport chain dysfunction involving elevated reactive oxygen species 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 with their ancestor.