Morphological Variation in the Skull of Nephelomys meridensis (Rodentia, Cricetidae): Evidence for Cryptic Species in Andean Populations from Northern South America

Abstract

The genus Nephelomys comprises at least 13 taxa with altitudinal distribution ranging from 900 to 4,000 meters above sea level. Three species are currently known to occur in Venezuela, but some authors suggest that two additional taxa are present in Venezuelan Andes populations and consider N. meridensis as a species complex. We conducted geometric morphometric analyses of skulls and jaws from populations assignable to the monotypic species N. meridensis from the Venezuelan Andes, in order to examine and compare morphological variations in this species. We compared four localities (including the type locality of N. meridensis) situated in northern, central, and western portions of Cordillera de Mérida and the Tamá páramo. We created morphological landmarks on dorsal, ventral, lateral, and jaw views of each skull using the tpsDIG software. Significant differences were found in skull shape and isometric size in most of the populations examined. The discrimination and morphological differentiation of some of these groups with respect to the population from the type locality (Mérida) were aligned with the results from multivariate and cytogenetic analyses carried out previously by other authors. Our data support recognizing N. meridensis as a species complex, comprising at least three still undescribed taxa from the Yacambú National Park (cordillera de Mérida), La Trampita (cordillera de Mérida) and the Tamá páramo (Tamá massif). A more detailed taxonomic study of Nephelomys from Venezuela, molecular and linear morphometric analyses, and revision of morphological characters, are necessary to describe potential new taxa and determine the geographical distribution of the species in this genus.