Conservation genetics of tree-kangaroos
A project undertaken at the Australian Museum, and supervised by Dr Mark Eldridge
Tree-kangaroos (Dendrolagus) are a unique, highly specialised and marvellously improbable group of macropods (kangaroos and wallabies) that are only found in the rainforests of Australia and New Guinea. Unlike other macropods (kangaroos and wallabies), tree-kangaroos are excellent climbers and spend most of their time in the forest canopy, where they feed on the leaves of trees and vines. In both Australia and New Guinea, tree-kangaroos are the largest tree-dwelling animals, and are increasingly being used as flagship species to promote rainforest biodiversity conservation. Most tree-kangaroo species are seriously threatened by people hunting them for food and the destruction of their forest habitat. Currently, 10 tree-kangaroo species are known (2 in Australia; 8 in New Guinea,) although the true number of species may be larger. In order to ensure the appropriate management of surviving tree-kangaroo populations, there is an urgent need to correctly identify the number of species and determine their inter-relationships.
A good understanding of the identity and number of species in a group (taxonomy) provides a firm scientific basis for management and conservation planning. Inadequate taxonomy can lead to erroneous and potentially disastrous management decisions; for example allowing a population to go extinct when it actually represented an unrecognised distinct species. Although the first tree-kangaroo species was described by western science in 1883, the group remains very poorly known, with four new species/subspecies being discovered and described by Australian Museum researchers since 1990. There is also considerable uncertainty about the status of many of the known species/subspecies. The most recent (1996) comprehensive review by Dr Tim Flannery recognised 10 species, although subsequently other authors have suggested there are 12 or maybe 14 species. This level of uncertainty and instability, is hampering efforts to develop and implement effective conservation measure for tree-kangaroos, especially in New Guinea, where all but one species is listed by the IUCN as threatened, with most being either 'endangered' and 'critically endangered'. Clearly, a thorough and detailed analysis of species boundaries within this group is required.
This project aimed to use DNA sequence data to establish the inter-relationships of tree-kangaroos in order to establish a clear and stable taxonomy that will underpin future conservation efforts. This project aimed to obtain DNA sequence data for multiple mitochondrial and nuclear genes from a comprehensive sample of tree-kangaroo specimens, representing as many described species/subspecies as possible.
We obtained DNA samples from representatives of 16 of the 17 known tree-kangaroo taxa (species/subspecies) from Museum collections, zoos and other researchers. We then generated ~3000bp of DNA sequence data from three mtDNA genes and ~5000bp of sequence data from five nuclear genes.
Phylogenetic analysis of these data revealed six well resolved, major tree-kangaroo lineages (see Figure 6): the 2 Australian species (D. bennettianus, D. lumholtzi); the grizzled tree-kangaroo (D. inustus), the black tree-kangaroo (D. ursinus) the dingiso (D. mbasio), a Goodfellow's group and a Doria's group. Within both of the Goodfellow's and Doria's groups there were 5-6 genetically well differentiated lineages, each of which appears to represent a distinct species. This suggests that there are more species within both the Goodfellow's and Doria's groups than is currently recognized and that the total number of species in the genus is likely to be 16, rather than the 10 species currently recognized. Morphological differences were also present between these lineages, although these were often subtle (Figures 3 & 4). Many of these tree-kangaroo taxa are poorly known, have restricted distributions, are highly threatened and should be a high priority for research and conservation efforts.
Our data suggest that tree-kangaroos originated in Australia and then spread to New Guinea where they underwent several episodes of diversification. There is no evidence for the migration of these New Guinean lineages back to Australia. The ancestral ‘long-footed’ and derived ‘short-footed’ groups proposed by Flannery received some short with the three short-footed species (bennettianus, lumholtzi, inustus) being placed more basally in the phylogenetic analysis. This study has greatly increased our understanding of tree-kangaroo evolution, has clarified the group’s inter-relations and identified key taxa for future conservation efforts.
Captions for Figures
Figure 1. Lumholtz’s tree-kangaroo is one of two species found in the wet tropics of north-east Queensland, Australia. (Photo © N Chaffer).
Figure 2. The Huon tree-kangaroo is one of eight species found in New Guinea. It is confined to the mountains of the Huon Peninsula. (Photo © William Betz).
Figure 3. Morphological variation within the Goodfellow’s complex of tree-kangaroos from New Guinea. Some of these variants are only known from a few specimens but are likely to represent distinct species. (Photo © Australian Museum).
Figure 4. Morphological variation within the Doria’s complex of tree-kangaroos from New Guinea. This project will seek to determine how many of these variants represent different species. (Photo © Australian Museum).
Figure 5. The grizzled tree-kangaroo is found in northern and western New Guinea and appears to represent an early offshoot in tree-kangaroo evolution (Photo © Pavel German).
Figure 6. Phylogenetic tree, based on mtDNA sequence data, showing relationships amongst the six major tree-kangaroo lineages and the multiple divergent lineages present within the Doria’s and Goodfellow’s groups.