Historical demography and spatial genetic structure of the subterranean rodent Ctenomys magellanicus in Tierra del Fuego (Argentina)

Abstract

Ctenomys (tuco-tuco) is the most numerous genus of South American subterranean rodents and one of the most genetically diverse clades of mammals known. In particular, the genus constitutes a very interesting model to evolutionary studies of genetic divergence and conservation. Ctenomys magellanicus is the southernmost species of the group and the only one living in Isla Grande de Tierra del Fuego (Argentina). This species presents two chromosomal forms (Cm34 and Cm36) fragmented into demes distributed from the north region (steppe) to the south region (ecotone) of the island respectively, no hybrids or overlapping areas were detected. In order to study the historical demography and the spatial genetic structure of C. magellanicus population we used mitochondrial DNA (D-loop and Cytochrome b) and microsatellite loci. Nine mtDNA haplotypes were identified, 3 of them belonging to the north and the other 6 to the south. Shared haplotypes between regions were not detected. Mitochondrial DNA and microsatellite genotypes showed a marked pattern of population structure with low values of genetic flow between regions. The south is made up of small populations or isolated demes making up an endogamic metapopulation with unique alleles and haplotypes. Also, the results suggest a northward expansion process starting from an ancestral haplotype from the south. That population might have lived at a refuge through the adverse Pleistocene environmental conditions that took place at Tierra del Fuego. Results of this study are relevant to the conservation of C. magellanicus suggesting that each region (north and south) might be considered as an Evolutionarily Significant Unit.