Molecular phylogenetics and phylogeographic structure of Sumichrast's harvest mouse (Reithrodontomys sumichrasti: Cricetidae) based on mitochondrial and nuclear DNA sequences.

Sumichrast's harvest mouse (Reithrodontomys sumichrasti) is a montane rodent species widely distributed through the Mesoamerican highlands. We used sequence data from one mitochondrial (cytochrome b) and two nuclear (β-fibrinogen and acid phosphatase type V) genes for a total of 1962 base pairs to estimate genealogical relationships and assess population genetic structure across the range of this taxon. Maximum likelihood and Bayesian approaches using cytochrome b resolved several major clades, revealing considerably more genetic diversity than observed in previous studies. The basal split in the tree topologies corresponded to the geographical separation among samples on either side of the Isthmus of Tehuantepec in México. We estimated an early Pleistocene or late Pliocene divergence between these two groups. We also recovered a well-supported clade south of the Nicaraguan Depression in Central America that we consider a separate biological species. The 12 networks generated using statistical parsimony (TCS) for cytochrome b sequence data were largely concordant with the phylogenetic analyses and we document the co-occurrence of two of these networks in central Veracurz. Phylogenies derived from β-fibrinogen and acid phosphatase type V gene segments revealed less phylogenetic signal and did not separate samples of R. sumichrasti east and west of the Isthmus of Tehuantepec. The phylogeny estimated by combining the mitochondrial and nuclear sequence data was essentially identical to the cytochrome b gene tree.