Baleen Whales Exhibit Unanticipated High Genetic Mutation Rate

A new estimate of the genetic mutation rate in four wild species of baleen whales suggests that these rates are higher than previous estimates, with some interesting implications for calculations of past whale abundance and low cancer rates. For instance, the new mutation rate determined by Marcos Suárez-Menéndez and colleagues reduces estimates of abundance in pre-exploitation whale populations by 86%, which has implications for population-rebuilding goals of whale conservation programs. The mutation rate—the probability of a nucleotide substitution per genetic site per generation—is difficult to calculate for many species but is used often to estimate important evolutionary and population changes. As A. Rus Hoelzel and Michael Lynch note in a related Perspective, mutation rates among nuclear genomes can vary 10,000-fold across all living organisms. Many mutation rate estimates come from a phylogeny approach, where mutations in similar parts of the genome are compared between related species that branched off from one another at known times in the past. The pedigree approach, which samples and measures mutations between generations of natural populations, provides a more direct estimate, but can be difficult to achieve in wild animals. Suárez-Menéndez et al. looked at mutation rates in nuclear and mitochondrial DNA from skin samples collected from North Atlantic blue, fin, bowhead, and humpback whales—21 genomes from parent-offspring "trios." The rates they calculated were much higher than had been previously calculated for large mammals, which are thought generally to have slow mutation rates. Instead, the researchers found the rate comparable to rates in primates and similar smaller bodied mammals. Among the implications of this new estimate: the relatively low rates of cancer among these giant mammals may not be related to a low mutation rate, as some have suggested.