Abstract Mitochondrial DNA (mtDNA) is a key molecular clock for studying evolutionary relationships and population history, but temporal inferences remain constrained by uncertainties in evolutionary rates. Previous analyses of the cytochrome b gene (Cytb) in Japanese rodents and shrews provided empirical rate estimates by linking mtDNA divergence patterns to rapid range expansion driven by repeated climatic shifts associated with the ∼100 000-year glacial cycle during the Middle Pleistocene. Motivated by these observations, this study investigated intraspecific divergence across six major mammalian lineages—Glires, Eulipotyphla, Chiroptera, Carnivora, Cetartiodactyla, and Primates—to test whether divergence is periodic and to compare evolutionary rates across phylogenetically diverse groups. Genetic differentiation (d) between major intraspecific lineages was assessed using publicly available mitochondrial Cytb sequences (mostly 1140 bp) and whole mitochondrial genome protein-coding sequences (ca. 11 400 bp). Analyses of half-distance (d/2) values, calibrated using palaeoclimatic markers, revealed multiple clusters within each taxonomic group that occur at broadly regular temporal intervals. These results provide evidence for periodic divergence in mammalian lineages and suggest that this global pattern may reflect the influence of Middle Pleistocene climate cycles. The results also indicate that mtDNA evolutionary rates are broadly consistent across taxa.
Hitoshi Suzuki (Sun,) studied this question.