Phylogenetic relationships of the cuscuses and brushtail possums (Marsupialia:Phalangeridae) using the nuclear gene BRCA1

Abstract

The family Phalangeridae comprises approximately two dozen extinct and extant species that include the brushtail possums (Trichosurus), scaly-tailed possum (Wyulda) and cuscuses (Phalanger, Strigocuscus, Spilocuscus and Ailurops). Morphological studies have suggested that Ailurops ursinus is the sister taxon to all other phalangerids. Another species of interest is Strigocuscus celebensis, whose morphologically based taxonomic affinity has habitually been with trichosurins. Mitochondrial 12S rRNA results, however, found moderate support for an Ailurops and Strigocuscus celebensis clade and placed A. ursinus and S. celebensis as sister to Phalanger and Spilocuscus. This study uses nuclear sequence data from the breast cancer and ovarian cancer susceptibility gene 1 (BRCA1) to test previous mitochondrial DNA results and uses relaxed molecular clock methods to estimate divergence dates. The results support Ailurops as sister taxon to S. celebensis and this clade as sister to Phalangerini. Relaxed molecular-dating methods suggest a date of 23–29 million years for the split between Trichosurini and the remaining phalangerids and 19–24 million years for the split between Ailurops + Strigocuscus celebensis and Phalangerini. Several vicariant/dispersal events are necessary to explain the geographic distribution of the Phalangeridae and our estimated molecular divergence dates are congruent with previously proposed south-east Asian geological events.