Molecular phylogenetics of Reig's short-tailed opossum (Monodelphis reigi) and its distributional range extension into Guyana

Reig's short-tailed opossum (Monodelphis reigi) was recently described morphologically, based on a single specimen from southeastern Venezuela. It was considered most similar to M. adusta, which is allopatrically distributed in the Andes and surrounding areas, but there has not been an explicit study of systematic relationships with other species of Monodelphis. We report the first occurrence from Guyana of this rare species that was previously known by only the holotype. In a molecular phylogenetic analysis of mitochondrial cytochrome b sequence variation, it groups within a well-supported monophyletic clade that includes M. adusta, M. handleyi, M. osgoodi, and M. peruviana. M. adusta was found to be the sister taxon to the rest of the adusta-complex. M. reigi is the basal taxon (sister species) of remaining adusta-complex forms. This corroborates earlier morphological studies suggesting close affinity of these taxa. As presently known, M. reigi is endemic to the highland regions (>1,000 m asl) of the Guiana Shield of northern South America, and is the only taxon within the M. adusta species complex that does not occur in the Andes or adjacent lowland regions. Based on previous molecular dating of Didelphidae, this suggests that there was a dispersal event from the Andes to the Guiana Highlands in the Miocene that gave rise to M. reigi.