The Late Pleistocene European small hamsters
The prevailing paleobiogeographic hypothesis posits that during the Pleistocene, steppe and tundra-steppe taxa currently found in Central Asia expanded into Europe during glacial periods, when open habitats prevailed. However, our previous findings show that European narrow-headed voles (Stenocranius anglicus) diverged from their Asiatic counterparts at least 200,000 years ago, implying their prolonged isolation and survival through at least one interglacial period in European refugia. To investigate whether this was an exception or part of a broader pattern, we analyzed mitochondrial genomes from 33 Late Pleistocene and Holocene remains of small hamsters (subfamily Cricetinae) originating from Central Europe, the Balkans, and Anatolia. Late Pleistocene small cricetids from Europe are typically attributed to the grey dwarf hamster (Nothocricetulus migratorius), a species currently distributed in Western and Central Asia and Eastern Europe. Surprisingly, among the 16 samples from Late Pleistocene Central Europe, only the hairy-footed hamster (Phodopus sungorus), now found in northern Kazakhstan and southern Russia, was identified. Phylogenetic analyses showed these specimens formed a sister clade to the lineage comprising all modern individuals. In contrast, all samples from the Balkans and Anatolia were assigned to N. migratorius. Phylogenetic reconstruction indicated that Holocene samples from Anatolia grouped with modern local populations, while Late Pleistocene samples from the Balkans formed a sister lineage to all extant individuals. In both cases, the divergence of the Late Pleistocene lineages was relatively recent, suggesting population continuity with the Late Pleistocene Asiatic source populations and likely the repeated population expansions, rather than long-term isolation in Europe. Our results suggest that, despite occupying broadly similar ecological niches, steppe species exhibit idiosyncratic responses to past climatic and environmental changes. Consequently, generalizations about their evolutionary histories may be unwarranted.