An emerging consensus in the evolution, phylogeny, and systematics of marsupials and their fossil relatives (Metatheria)

Marsupials and their fossil relatives, which collectively comprise Metatheria, have been of scientific interest for centuries, with many aspects of their evolution and systematics subject to intense research and debate. Here, we review progress over the last 25 years, which has included the description of many new species (modern and fossil), and major improvements in understanding of their phylogenetic relationships, as well as the overall evolutionary history and biogeography of Marsupialia (crown-clade) and Metatheria (total-clade). Significant advances have included the deployment of increasingly sophisticated molecular, morphological, and total evidence analyses, which have resolved most previously disputed relationships among and within the modern marsupial orders. A broad systematic consensus is now emerging, although several major areas of contention remain, particularly among fossil metatherians. New modern species continue to be described at an impressive rate, with almost 50 named in the last 25 years, and many more await discovery. There has also been an explosion in the discovery and description of fossil marsupials and non-marsupial metatherians (~270 species), principally from Australasia and the Americas but also from Antarctica, Europe, and Asia. Most are represented by dental specimens only, but some consist of complete and well-preserved material, which has led to major improvements in our understanding of the evolution of cranial and postcranial morphology. Improvements in the fossil record and advances in methods for inferring divergence times have helped clarify when and where key events occurred in metatherian evolution, and the patterns of subclade diversification. We also have improved understanding of biogeographical relationships among metatherians on different landmasses. Despite enormous progress, numerous key uncertainties remain due to major gaps in the fossil record (e.g., Antarctica, Late Cretaceous, and early Paleogene of Australia) and a comparative lack of studies that directly combine molecular and fossil data. Future advances will largely depend on improvements in the fossil record and studies that better integrate neontological and paleontological evidence

Ancient DNA Elucidates the Controversy about the Flightless Island Hens (Gallinula sp.) of Tristan da Cunha

A persistent controversy surrounds the flightless island hen of Tristan da Cunha, Gallinula nesiotis. Some believe that it became extinct by the end of the 19th century. Others suppose that it still inhabits Tristan. There is no consensus about Gallinula comeri, the name introduced for the flightless moorhen from the nearby island of Gough. On the basis of DNA sequencing of both recently collected and historical material, we conclude that G. nesiotis and G. comeri are different taxa, that G. nesiotis indeed became extinct, and that G. comeri now inhabits both islands. This study confirms that among gallinules seemingly radical adaptations (such as the loss of flight) can readily evolve in parallel on different islands, while conspicuous changes in other morphological characters fail to occur

Adaptation and conservation insights from the koala genome

The koala, the only extant species of the marsupial family Phascolarctidae, is classified as ‘vulnerable’ due to habitat loss and widespread disease. We sequenced the koala genome, producing a complete and contiguous marsupial reference genome, including centromeres. We reveal that the koala’s ability to detoxify eucalypt foliage may be due to expansions within a cytochrome P450 gene family, and its ability to smell, taste and moderate ingestion of plant secondary metabolites may be due to expansions in the vomeronasal and taste receptors. We characterized novel lactation proteins that protect young in the pouch and annotated immune genes important for response to chlamydial disease. Historical demography showed a substantial population crash coincident with the decline of Australian megafauna, while contemporary populations had biogeographic boundaries and increased inbreeding in populations affected by historic translocations. We identified genetically diverse populations that require habitat corridors and instituting of translocation programs to aid the koala’s survival in the wild

Evolution: the evolutionary rat race in New Guinea and Australia

A new molecular phylogeny of a remarkable radiation of New Guinean and Australian rodents indicates multiple transitions between biomes and biogeographical regions within the group, and suggests that a key role was played by the geological history of New Guinea

Testing the ability of topoclimatic grids of extreme temperatures to explain the distribution of the endangered brush-tailed rock-wallaby (Petrogale penicillata)

Aim: Many species are susceptible to climatic extremes, yet few fine-scale studies consider the factors that determine the distribution of extreme temperatures at landscape and regional scales. These factors include cold air drainage, canopy cover and topographical exposure to winds and radiation. We used the brush-tailed rock-wallaby (Petrogale penicillata) to test whether innovative topoclimatic grids of extreme temperatures are an important predictor of regional-scale species distributions. Location: Hunter Valley region, New South Wales, Australia (31.2-33.4° S, 148.6-153.0° E). Methods: We modelled the regional distributions of rock-wallaby observations and colonies using topoclimatic, macroclimatic, topographical and habitat factors. We employed a randomization procedure to reduce spatial clustering of records and divide the data into 10 different training and testing datasets. Models were assessed using the Akaike information criterion (AIC) on the training datasets, the area under the receiver operating characteristic curve (AUC) on the test datasets, and the consistency of the response curves. We compared multiple univariate and multivariate models, rather than producing one 'true' model, to examine the evidence that different environmental factors consistently influenced the distribution of rock-wallabies. Results: The environmental factors that were consistently strongest at explaining the distribution of rock-wallabies were the topoclimatic estimate of extreme cold, the macroclimatic estimate of annual precipitation, and the amount of cleared land within 1600 m. Rock-wallaby colonies were in areas where minimum temperatures were high, rainfall was low, and there was a low proportion of cleared land. Topographical surrogates performed well in univariate models but poorly in multivariate models. Main conclusions: We have shown that topoclimatic maps of extreme conditions have the potential to model the regional distributions of at least some species better than indirect surrogates based on topography or macroclimate. Topoclimatic grids are an important tool for regional conservation planning, but practitioners need to place more emphasis on the derivation and accuracy of the climate grids, not just the spatial resolution. © 2014 John Wiley & Sons Ltd