Evolution of the Grey-bellied pygmy mouse group: Highly structured molecular diversity with predictable geographic ranges but morphological crypsis.

The grey-bellied pygmy mouse (Mus triton) from the endemic African subgenus Nannomys is a widespread rodent species inhabiting the highlands of eastern and central Africa. Although it has long been considered as a single species, recent data has suggested the existence of a species complex. In order to evaluate the geographical structure and current taxonomy of M. triton, we analysed one mitochondrial and six nuclear genes from individuals covering most of its distribution range. Our analysis revealed the existence of at least five distinct genetic lineages with only marginal overlaps among their distributional ranges. Morphological comparisons, however, showed large overlaps in external body measurements and only a weak differentiation in skull form. Therefore, we suggest maintaining M. triton as a single taxon with pronounced intraspecific genetic structure. Divergence dating analysis placed the most recent common ancestor of the extant lineages of M. triton to the early Pleistocene (about 2.0 Ma). The phylogeographic structure of the species was likely shaped by Pleistocene climatic oscillations and the highly diverse topography of eastern Africa.

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