Geographic dimorphism in the mountain brushtail possum (Trichosurus caninus): the case for a new species

Abstract

The morphological and genetic characteristics of the mountain brushtail possum (Trichosurus caninus) are described for animals from a range of locations throughout its known geographic distribution in eastern Australia. Although there is considerable variation among populations, unequivocal morphological and genetic differences exist between northern and southern populations of the species. Specimens from southern populations (from Victoria) have a significantly (P < 0.001) larger ear conch, a significantly (P < 0.001) longer pes, and a significantly (P < 0.001) shorter tail than do specimens from northern populations (from New South Wales and Queensland). Animals can be clearly distinguished using a simple index based on these three morphological measures, which are gathered from live animals. North-south dimorphism is strongly supported by patterns in genetic data that show genetic distances of 2.7-3.0% between the southern and northern populations. The combined outcomes of morphological and genetic analyses suggest the existence of two distinct species. We recommend that the northern form, distributed from central New South Wales north to central Queensland, retain the name Trichosurus caninus; the southern form from Victoria is described here as Trichosurus cunninghami, sp. nov. The common names of these new species should be the 'short-eared possum' and the 'mountain brushtail possum', respectively.