Tree-kangaroos Dendrolagus in Australia: Are D. lumholtzi and D. bennettianus sister taxa?

Tree-kangaroos Dendrolagus sp. are a poorly known group of folivorous arboreal macropodid marsupials endemic to the rainforests of north-eastern Australia and New Guinea. Over the last century there has been little agreement on the relationship between the two Australian species, D. lumholtzi and D. bennettianus. In light of this uncertainty, we undertook a phylogenetics study based on 430 bp of sequence from the mitochondrial DNA gene cytochrome b (cytb). Samples were collected from D. lumholtzi (n=45) and D. bennettianus (n=3), as well as representative of six New Guinean Dendrolagus species. Results from distance and parsimony analyses strongly support a sister relationship between the two Australian species. However, D. lumholtzi and D. bennettanius show considerable sequence divergence (5.3%), suggesting that their speciation predates the mid-late Pleistocene. Although inter-relationships amongst New Guinean Dendrolagus were not fully resolved by our preliminary analysis, a number of distinct lineages are apparent. D. goodfellowi, D. matschiei and D. spadix form a monophyletic group of closely related taxa, as do the two sampled subspecies of D. dorianus. However, unexpectedly large divergences were obtained both between these subspecies (7.4%) and within one of them (D. d. stellerum, 7.8%). This suggests that D. dorianus may actually consist of a complex of related species, but more extensive research is required.