Résumé
Mitochondrial DNA (mtDNA) is the most popular marker of molecular
diversity in animals, primarily because of its elevated mutation rate.
After >20 years of intensive usage, the extent of mitochondrial
evolutionary rate variations across species, their practical consequences
on sequence analysis methods, and the ultimate reasons for mtDNA
hypermutability are still largely unresolved issues. Using an extensive
cytochrome b data set, fossil data, and taking advantage of the decoupled
dynamics of synonymous and nonsynonymous substitutions, we measure the
lineage-specific mitochondrial mutation rate across 1,696 mammalian
species and compare it with the nuclear rate. We report an unexpected 2
orders of magnitude mitochondrial mutation rate variation between
lineages: cytochrome b third codon positions are renewed every 1-2 Myr, in
average, in the fastest evolving mammals, whereas it takes >100 Myr
in slow-evolving lineages. This result has obvious implications in the
fields of molecular phylogeny, molecular dating, and population genetics.
Variations of mitochondrial substitution rate across species are partly
explained by body mass, longevity, and age of female sexual maturity. The
classical metabolic rate and generation time hypothesis, however, do not
fully explain the observed patterns, especially a stronger effect of
longevity in long-lived than in short-lived species. We propose that
natural selection tends to decrease the mitochondrial mutation rate in
long-lived species, in agreement with the mitochondrial theory of aging.