Systematics and evolutionary history of the genus Micromys (Mammalia: Rodentia: Muridae)

The genus Micromys is one of the smallest-sized rodents widely distributed in temperate regions of Eurasia. However, its taxonomy and evolutionary history remain unresolved. In this study, we analyzed the phylogenetic and morphological relationships of Micromys species using two mitochondrial genes, three nuclear genes, and a morphological dataset. We also analyzed its geographical distribution structure using 140 cytochrome b ( Cyt b ) gene sequences. Our results supported the existence of three species in the genus Micromys : M. minutus , M. erythrotis , and M. pygmaeus , which was previously considered a subspecies of M. minutus or M. erythrotis . Micromys minutus is widely distributed in Europe and North-East Asia, M. erythrotis is distributed in central and southern China, Vietnam, Myanmar, and India, and M. pygmaeus is restricted to the middle-to-high elevations of the Himalayas and Hengduan Mountains (1600–3800 m). Phylogenetic analyses indicated that M. pygmaeus is a sister species to M. erythrotis, with a p -distance of 11.4% ( Cyt b ) and 9.2% ( COI ) between them. The divergence between M. minutus and M. pygmaeus + M. erythrotis occurred ca. 3.35 Ma, while M. pygmaeus and M. erythrotis diverged ca. 2.55 Ma. The divergence of the Micromys species was likely affected by the rapid uplift of the Tibetan Plateau and Hengduan Mountains, and the global cooling and desiccating events at the Pliocene/Pleistocene boundaries.