The Peromyscus maniculatus species complex is one of the most widespread group of small mammals in North America. However, the taxonomy and phylogenetic relationships among its constituent taxa remain unclear. As part of a revision of Peromyscus specimens from the highlands of the Trans-Mexican Volcanic Belt in central Mexico, we identified five individuals collected in 1968 that differed externally from other Peromyscus specimens, although morphologically similar to P. labecula and P. melanotis, both latter in the P. maniculatus species complex. Based on cranial measurements and mitochondrial DNA sequences, we aimed to more accurately determine the phylogenetic relationships and the taxonomic status of these individuals. Molecular phylogenetic analyses showed that the specimens formed a monophyletic clade sister to the P. maniculatus species complex. Pairwise genetic distances between those specimens and other species within the P. maniculatus species complex were greater than 7.91%. In addition, morphological analyses clearly distinguished the test specimens from P. melanotis and P. labecula. Based on the results of our molecular and morphological analyses, we conclude that these specimens represent an undescribed species of the P. maniculatus species complex, which we describe herein. El complejo de especies de P. maniculatus es uno de los grupos de pequeños mamíferos más ampliamente distribuídos en Norteamérica. Sin embargo, la taxonomía y relaciones filogenéticas de sus especies constituyentes siguen inciertas. Como parte de una revisión de los ejemplares de Peromyscus de las zonas montañosas de la Eje Volcánico Transversal de Mexico, encontramos cinco especímenes colectados en 1968 que eran diferentes externamente de otros especímenes de Peromyscus. Estos cinco ejemplares eran parecidos morfológicamente a P. labecula y P. melanotis del complejo de especies de P. maniculatus. Basándonos en mediciones craneales y secuencias de ADN mitocondrial, determinamos las relaciones filogenéticas y estatus taxonómico de estos individuos. El análisis filogenético demostró que los especímenes forman un clado monofilético, hermano al complejo de especies de P. maniculatus. Las distancias genéticas entre el clado representado por los cinco especimenes con respecto a las otras especies del complejo P. maniculatus son superiores al 7.91%. Asimismo, los análisis morfológicos distinguieron claramente a estos individuos de P. melanotis y P. labecula. Con base en los resultados de nuestros análisis moleculares y morfológicos, concluimos que estos cinco especímenes representan una especie no descrita del complejo de especies de P. maniculatus, la cual describimos aquí.

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The Tropical Montane Cloud Forest (TMCF) is a highly dynamic ecosystem that has undergone frequent spatial changes in response to the interglacial-glacial cycles of the Pleistocene. These climatic fluctuations between cold and warm cycles have led to species range shifts and contractions-expansions, resulting in complex patterns of genetic structure and lineage divergence in forest tree species. In this study, we sequenced four regions of the chloroplast DNA (trnT-trnL, trnK5-matk, rpl32-trnL, trnS-trnG) for 20 populations and 96 individuals to evaluate the phylogeography, historical demography, and paleodistributions of vulnerable endemic TMCF trees in Mexico: Magnolia pedrazae (north-region), M. schiedeana (central-region), and M. schiedeana population Oaxaca (south-region). Our data recovered 49 haplotypes that showed a significant phylogeographic structure in three regions: north, central, and south. Bayesian Phylogeographic and Ecological Clustering (BPEC) analysis also supported the divergence in three lineages and highlighted the role of environmental factors (temperature and precipitation) in genetic differentiation. Our historical demography analyses revealed demographic expansions predating the Last Interglacial (LIG, ~125,000 years ago), while Approximate Bayesian Computation (ABC) simulations equally supported two contrasting demographic scenarios. The BPEC and haplotype network analyses suggested that ancestral haplotypes were geographically found in central Veracruz. Our paleodistributions modeling showed evidence of range shifts and expansions-contractions from the LIG to the present, which suggested the complex evolutionary dynamics associated to the climatic oscillations of the Pleistocene. Habitat management of remnant forest fragments where large and genetically diverse populations occur in the three TMCF regions analyzed would be key for the conservation of these magnolia populations.