Bengal Slow Loris - Taxonomy and Phylogeny

Taxonomy and Phylogeny

Nycticebus bengalensis, commonly known as the Bengal slow loris or northern slow loris, is a strepsirrhine primate in the slow loris genus, Nycticebus. Formerly considered a subspecies of the Sunda slow loris (N. coucang), it was recognized as a distinct species in 2001 by taxonomist and primatologist Colin Groves. It is difficult to distinguish from the other species in its genus.

To help clarify species and subspecies boundaries, and to establish whether morphology-based classifications were consistent with evolutionary relationships, the phylogenetic relationships within the genus Nycticebus have been investigated using DNA sequences derived from the mitochondrial markers D loop and cytochrome b. Although most of the recognized lineages of Nycticebus (including N. pygmaeus, N. menagensis and N. javanicus) were shown to be genetically distinct—the analysis suggested that DNA sequences from some individuals of N. coucang and N. bengalensis apparently share a closer evolutionary relationship with each other than with members of their own species. The authors suggest that this result may be explained by introgressive hybridization, as the tested individuals of these two taxa originated from a region of sympatry in southern Thailand; the precise origin of one of the N. coucang individuals was not known. This hypothesis was corroborated by a 2007 study that compared the variations in mitochondrial DNA sequences between N. bengalensis and N. coucang, and suggested that there has been gene flow between the two species.