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Transitions to Asexuality Result in Excess Amino Acid Substitutions
Susanne Paland and
Michael Lynch
Theory predicts that linkage between genetic loci reduces theefficiency of purifying selection. Because of the permanentlinkage of all heritable genetic material, asexual lineagesmay be exceptionally prone to deleterious-mutation accumulationin both nuclear and organelle genes. Here, we show that theratio of the rate of amino acid to silent substitution (Ka/Ks)in mitochondrial protein-coding genes is higher in obligatelyasexual lineages than in sexual lineages of the microcrustaceanDaphnia pulex. Using a phylogeny-based approach to quantifythe frequency of mutational-effect classes, we estimate thatmitochondrial protein-coding genes in asexual lineages accumulatedeleterious amino acid substitutions at four times the ratein sexual lineages. These results support the hypothesis thatsexual reproduction plays a prominent role in reducing the mutationalburden in populations.
Department of Biology, Indiana University, 1001 East 3rd Street, Bloomington, IN 47405, USA.
