Impacts of late Quaternary environmental change on the long-tailed ground squirrel (Urocitellus undulatus) in Mongolia

Abstract

Impacts of Quaternary environmental changes on mammal faunas of central Asia remain poorly understood due to a lack of geographically comprehensive phylogeographic sampling for most species. To help address this knowledge gap, we conducted the most extensive molecular analysis to date of the long-tailed ground squirrel (Urocitellus undulatus Pallas 1778) in Mongolia, a country that comprises the southern core of this species' range. Drawing on material from recent collaborative field expeditions, we genotyped 128 individuals at 2 mitochondrial genes (cytochrome b and cytochrome oxidase I; 1 797 bp total). Phylogenetic inference supports the existence of two deeply divergent infraspecific lineages (corresponding to subspecies U. u. undulatus and U. u. eversmanni), a result in agreement with previous molecular investigations but discordant with patterns of range-wide craniometric and external phenotypic variation. In the widespread westerneversmanni lineage, we recovered geographically-associated clades from the: (a) Khangai, (b) Mongolian Altai, and (c) Govi Altai mountain ranges. Phylogeographic structure in U. u. eversmanni is consistent with an isolation-by-distance model; however, genetic distances are significantly lower than among subspecies, and intra-clade relationships are largely unresolved. The latter patterns, as well as the relatively higher nucleotide polymorphism of populations from the Great Lakes Depression of northwestern Mongolia, suggest a history of range shifts into these lowland areas in response to Pleistocene glaciation and environmental change, followed by upslope movements and mitochondrial lineage sorting with Holocene aridification. Our study illuminates possible historical mechanisms responsible for U. undulatus genetic structure and contributes to a framework for ongoing exploration of mammalian response to past and present climate change in central Asia.