Phylogeography of the narrow-headed vole Lasiopodomys (Stenocranius ) gregalis (Cricetidae, Rodentia) inferred from mitochondrial cytochrome b sequences: an echo of Pleistocene prosperity

Abstract

A species-wide phylogeographic study of the narrow-headed vole Lasiopodomys (Stenocranius) gregalis was performed using the mitochondrial (mt) cytochrome b gene. We examined 164 specimens from 50 localities throughout the species distribution range. Phylogeographic pattern clearly demonstrates the division into four major mtDNA lineages with further subdivision. The level of genetic differentiation between them was found to be extremely high even for the species level: about 6–11%. The most striking result of our study is extremely high mutation rate of cytb in L. gregalis. Our estimates suggested its value of 3.1 × 10−5 that is an order of magnitude higher than previous estimates for Microtus species. The mean estimated time of basal differentiation of the narrow-headed vole is about 0.8 Mya. This time estimate is congruent with the known paleontological record. The greatest mitochondrial diversity is found in Southern Siberia where all four lineages occur; therewith, three of them are distributed exclusively in that area. The lineage that is distributed in south-eastern Transbaikalia is the earliest derivate and exhibits the highest genetic divergence from all the others (11%). It is quite probable that with further research, this lineage will turn out to represent a cryptic species. Spatial patterns of genetic variation in populations of the narrow-headed vole within the largest mt lineage indicate the normal or stepping stone model of dispersal to the north and south-west from the Altay region in Middle Pleistocene. Both paleontological data and genetic diversity estimates suggest that this species was very successful during most of the Pleistocene, and we propose that climate humidification and wide advance of tree vegetation at the Pleistocene–Holocene boundary promoted range decrease and fragmentation for this typical member of tundra-steppe faunistic complex. However, we still observe high genetic diversity within isolated fragments of the range.