Meeting Abstract
To reveal phenotypic and functional genomic patterns of mitonuclear adaptation, a laboratory adaptation study with Caenorhabditis elegans nematodes was conducted in which independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain (ETC) mutant, gas-1. Following evolution, 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 gas-1 mutant ancestor, and a high-fitness class containing lines that exhibited partial recovery of wildtype 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 accompanied or facilitated by outcrossing. A highly non-random pattern of mitochondrial DNA mutation was observed within high-fitness gas-1 lines, with parallel fixations of nonsynonymous base substitutions affecting gene products residing within ETC Complex I alongside the nuclear-encoded GAS-1 protein. Individual characterization of one of these mutations suggest that it was causal in the line’s fitness recovery. Results provide convincing evidence for adaptation via mitonuclear epistasis, and indicate that mtDNA can be an important contributor to such evolution. Results will be discussed within the context of current hypotheses regarding mitonuclear adaptation and the evolution and maintenance of outcrossing.
