Project description:The Reithrodontomys tenuirostris species group is considered "the most specialized" within the genus Reithrodontomys from morphological and ecological perspectives. Previous studies based on molecular data recommended changes in the taxonomy of the group. In particular, R. microdon has been the most taxonomically questioned, with the suggestion that it constitutes a complex of cryptic species. We analyzed the phylogenetic relationships of the R. tenuirostris species group using DNA sequences from the mitochondrial Cytochrome b gene and Intron 7 of the nuclear beta fibrinogen gene. In addition, divergence times were estimated, and possible new taxa delimited with three widely used species delimitation methods. Finally, possible connectivity routes based on shared haplotypes were tested among the R. microdon populations. All species were recovered as monophyletic with the exception of R. microdon, whose individuals were grouped into four different haplogroups, one of which included specimens of R. bakeri. Diversification within the R. tenuirostris species group began about 3 Ma, in the Pleistocene. The bGMYC and STACEY delimitation methods were congruent with each other, delimiting at the species-level each haplogroup within R. microdon, while the mPTP suggested a greater number of species. Moreover, none of the haplogroups showed potential connectivity routes between them, evidencing lack of gene flow. Our results suggest the existence of a higher number of species in the R. tenuirostris group, because we show that there are four species within what is currently recognized as R. microdon.
