Purging Deleterious Mutations under Self Fertilization: Paradoxical Recovery in Fitness with Increasing Mutation Rate in Caenorhabditis elegans

• Published in: PloS one Vol. 5; no. 12; p. e14473
• Main Authors: Morran, Levi T., Ohdera, Aki H., Phillips, Patrick C.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 31.12.2010; Public Library of Science (PLoS)
• Subjects: Accumulation; Animals; Caenorhabditis briggsae; Caenorhabditis elegans; Caenorhabditis elegans - genetics; Caenorhabditis elegans - physiology; DNA Mutational Analysis; Dose-Response Relationship, Drug; Ecology; Epistasis; Epistasis, Genetic; Ethyl Methanesulfonate - toxicity; Evolution & development; Evolutionary biology; Evolutionary Biology/Animal Genetics; Evolutionary Biology/Evolutionary Ecology; Evolutionary Biology/Sexual Behavior; Fertilization; Fitness; Gene Deletion; Genetic aspects; Genetic Linkage; Genetics; Genetics and Genomics/Population Genetics; Genomes; Laboratories; Linkage Disequilibrium; Loci; Models, Genetic; Morphology; Mutagenesis; Mutagens; Mutation; Mutation rates; Nematodes; Organisms; Population; Populations; Purging; Recovery (Medical); Reproductive fitness; Self-fertilization; Self-Fertilization - genetics; Trends; Worms; Oregon; Indiana; United States > US
• DOI: 10.1371/journal.pone.0014473
• ISSN: 1932-6203

The accumulation of deleterious mutations can drastically reduce population mean fitness. Self-fertilization is thought to be an effective means of purging deleterious mutations. However, widespread linkage disequilibrium generated and maintained by self-fertilization is predicted to reduce the efficacy of purging when mutations are present at multiple loci. We tested the ability of self-fertilizing populations to purge deleterious mutations at multiple loci by exposing obligately self-fertilizing populations of Caenorhabditis elegans to a range of elevated mutation rates and found that mutations accumulated, as evidenced by a reduction in mean fitness, in each population. Therefore, purging in obligate selfing populations is overwhelmed by an increase in mutation rate. Surprisingly, we also found that obligate and predominantly self-fertilizing populations exposed to very high mutation rates exhibited consistently greater fitness than those subject to lesser increases in mutation rate, which contradicts the assumption that increases in mutation rate are negatively correlated with fitness. The high levels of genetic linkage inherent in self-fertilization could drive this fitness increase. Compensatory mutations can be more frequent under high mutation rates and may alleviate a portion of the fitness lost due to the accumulation of deleterious mutations through epistatic interactions with deleterious mutations. The prolonged maintenance of tightly linked compensatory and deleterious mutations facilitated by self-fertilization may be responsible for the fitness increase as linkage disequilibrium between the compensatory and deleterious mutations preserves their epistatic interaction.