Phylogeography and demographic history of the subterranean rodents belonging to the Ctenomys talarum phylogenetic group (Rodentia: Ctenomyidae)

The genus Ctenomys is the most speciose of all known subterranean rodents. Currently, most species of this genus are included in eight distinctive phylogenetic groups. The Ctenomys talarum phylogenetic group has remained invariant in terms of the number of species in recent years. This group of species forms a well-supported monophyletic clade composed of the nominal species Ctenomys talarum (Thomas 1898) and Ctenomys pundti (Nehring 1900), which are distributed in the pampas region, a vast plains extending westward across Central Argentina from the Atlantic coast to the Andean foothills. This phylogenetic group also includes some Pampean populations with an uncertain taxonomic status but geographically close to the distribution of C. pundti. These populations were originally associated with C. pundti and called in conjunction C. pundti complex. Due to the phylogenetic proximity between populations of this complex and C. talarum, the phylogenetic relationships within the C. talarum group are currently under review. Here we use mitochondrial DNA sequences of the non-coding region of D-loop (434 bp) to assess the historical demography and phylogeography of populations belonging to the C. talarum group. This study includes individuals from populations sampled across a wide region (approximately 518,000 km2) in Central Argentina. Analysis of molecular variance (AMOVA) and pairwise ФST estimates between sampling locations showed significant population genetic substructure at local and regional levels. However, phylogeographic genetic subdivision in the C. talarum group is rather weak and does not follow a pattern of isolation by distance. In this way, Bayesian analyses showed a weak signal of demographic expansion followed by a small reduction in the effective population size (Ne), which occurred approximately 2000 years before present (ybp). This reduction in the Ne was probably due to changes in the landscape configuration during the Late Holocene. According to our results and paleontological records, current populations of the C. talarum group are likely remnants of a much broader and more continuous historical distribution in the Pampas region. Finally, phylogenetic analyses (Bayesian and Maximum Likelihood inferences) showed that populations previously assigned to the C. pundti complex should be referred to belonging to C. talarum.