Phylogenetic affinities and species limits within the genus Megadontomys (Rodentia: Cricetidae) based on mitochondrial sequence data

The evolutionary history of the genus Megadontomys, a group of mice allopatrically distributed along the cool-humid forest in the highlands of Mexico, is controversial. In this study, we examined phylogenetic relationships within the genus using sequences data from the complete mitochondrial cytochrome b gene. This information also allowed us to corroborate species limits, geographic boundaries of taxonomic entities and assess genetic variation within each taxon. The results of the phylogenetic analyses based on maximum likelihood, Bayesian inference and maximum parsimony were largely congruent in that M. nelsoni and M. thomasi were more closely related relative to M. cryophilus. These results are concordant with previous studies based on morphology and allozyme variation. However, testing of the alternative hypothesis of a closer evolutionary affinity between M. nelsoni M. cryophilus did not produce a significantly less likely tree. The lack of unambiguous support towards one of these previously proposed contending hypotheses is congruent with the alternative scenario of an almost simultaneous diversification of the three species. Application of the phylogenetic species concept and the genetic species concept supports the recognition of three distinct taxonomic entities at the specific level. M. nelsoni inhabits the Sierra Madre Oriental (Hidalgo, Veracruz, and Puebla) including the Sierra Mazateca (Oaxaca); M. cryophilus is restricted to the Sierra de Juarez (Oaxaca); and M. thomasi occurs in portions of the Sierra Madre del Sur (Guerrero) and the Sierra Mixteca (Oaxaca). Our data show that M. thomasi is formed by two genetically distinct lineages that potentially may represent distinct Evolutionary Significant Units.