The deep divergence of marsupials and eutherian mammals 160 million years ago provides genetic variation to explore the evolution of DNA sequence, gene arrangement and regulation of gene expression in mammals. Following the pioneering work of Professor Desmond W. Cooper, emerging techniques in cytogenetics and molecular biology have been adapted to characterise the genomes of kangaroos and other marsupials. In particular, genetic and genomic work over four decades has shown that marsupial sex chromosomes differ significantly from the eutherian XY chromosome pair in their size, gene content and activity. These differences can be exploited to deduce how mammalian sex chromosomes, sex determination and epigenetic silencing evolved.

Marsupial and eutherian mammals inactivate one X chromosome in female somatic cells in what is thought to be a means of compensating for the unbalanced X chromosome dosage between XX females and XY males. The hypothesis of X chromosome inactivation (XCI) was first published by Mary Lyon just over 50 years ago, with the discovery of XCI in marsupials occurring a decade later. However, we are still piecing together the evolutionary origins of this fascinating epigenetic mechanism. From the very first studies on marsupial X inactivation, it was apparent that, although there were some similarities between marsupial and eutherian XCI, there were also some striking differences. For instance, the paternally derived X was found to be preferentially silenced in marsupials, although the silencing was often incomplete, which was in contrast to the random and more tightly controlled inactivation of the X chromosome in eutherians. Many of these earlier studies used isozymes to study the activity of just a few genes in marsupials. The sequencing of several marsupial genomes and the advent of molecular cytogenetic techniques have facilitated more in-depth studies into marsupial X chromosome inactivation and allowed more detailed comparisons of the features of XCI to be made. Several important findings have come from such comparisons, among which is the absence of the XIST gene in marsupials, a non-coding RNA gene with a critical role in eutherian XCI, and the discovery of the marsupial RSX gene, which appears to perform a similar role to XIST. Here I review the history of marsupial XCI studies, the latest advances that have been made and the impact they have had towards unravelling the evolution of XCI in mammals.

Marsupial immune responses were previously touted as ‘primitive’ but we now know that the marsupial immune system is complex and on par with that of eutherian mammals. In this manuscript we review the field of marsupial immunology, focusing on basic anatomy, developmental immunology, immunogenetics and evolution. We concentrate on advances to our understanding of marsupial immune gene architecture, made possible by the recent sequencing of the opossum, tammar wallaby and Tasmanian devil genomes. Characterisation of immune gene sequences now paves the way for the development of immunological assays that will allow us to more accurately study health and disease in marsupials.

Extant mammals are divided into sub- and infraclasses that are distinguished by their mode of reproduction. The monotremes lay eggs, the marsupials give birth to altricial young that typically develop in a pouch, and the eutherians have prolonged in utero development, resulting in well developed young at birth. The three groups exhibit what appears to be a nice progression of evolution towards the well developed newborn young of eutherian mammals. However, marsupials do not represent a step in the progression of producing well developed young, but maintain a reproductive strategy that has evolved to prosper in their specific niche. The production of undeveloped young with increased development in the pouch (or counterpart) provides specific advantages to those species living in diverse environments. The evolution of this reproductive strategy provides a clever solution to the uncertain and often adverse conditions encountered by many species, and the survival of the developing young in a pouch containing potentially harmful microorganisms is truly remarkable. In this review, we explore the unique features of the pouch, highlight the research questions that remain unanswered regarding this unique marsupial attribute and discuss the advantages of the marsupial reproductive strategy and the potential role of the pouch in mammalian diversification.

Bats are the second most species rich and abundant group of mammals and display an array of unique characteristics but are also among the most poorly studied mammals. They fill an important ecological niche and have diversified into a wide range of habitats. In recent years, bats have been implicated as reservoirs for some of the most highly pathogenic emerging and re-emerging infectious diseases reported to date, including SARS-like coronavirus, Ebola, Hendra and Nipah viruses. The ability of bats to harbour these viruses in the absence of clinical signs of disease has resulted in a resurgence of interest in bat biology and virus–host interactions. Interest in bats, in Australia in particular, has intensified following the identification of several novel bat-borne viruses from flying-foxes, including Hendra virus, which is capable of spillover from bats to horses and subsequently to humans with potentially fatal consequences. As we continue to encroach on the natural habitats of bats, a better understanding of bat biology, ecology and virus–host interactions has never before been so critical. In this review, we focus on the biology of Australian pteropid bats and the pathogens they harbour, summarising current knowledge of bat-borne diseases, bat ecology, ethology and immunology.

There are several aspects of biology in which the contribution of males and females is unequal. In these instances the examination of Y chromosome markers may be used to elucidate male-specific attributes. Here, male dispersal patterns and genetic structuring were examined using four Y-microsatellite loci in 186 male western grey kangaroos, Macropus fuliginosus, from throughout the species’ trans-continental distribution. In addition, 52 male grey kangaroos were examined to investigate hybridisation between M. fuliginosus and the eastern grey kangaroo, Macropus giganteus, in their region of sympatry in eastern Australia. Detected Y chromosome diversity was low, resulting from low effective male population size due to skewed sex ratios and a polygynous mating system. As expected, male dispersal was high across the range. However, the Lake Torrens–Flinders Ranges region appears to have significantly restricted male movement between eastern and central/western Australia. There was little evidence to suggest that other barriers (Nullarbor Plain and Swan River Valley) previously identified by nuclear and mitochondrial DNA marker studies restrict male movement. Hence, the admixture events previously identified may be associated with high male dispersal. Within the region of sympatry between M. fuliginosus and M. giganteus in eastern Australia, four M. giganteus individuals were found to possess M. fuliginosus Y-haplotypes. These results confirm the occurrence of hybridisation between male M. fuliginosus and female M. giganteus. Additionally, the introgression of M. fuliginosus Y-haplotypes into M. giganteus populations indicates that at least some male hybrids are fertile, despite evidence to the contrary from captive studies. This study has provided insights into the male contribution to population history, structure and hybridisation in M. fuliginosus, which were not predicted by comparisons between biparentally and maternally inherited markers. This highlights the importance of direct examination of the Y chromosome to provide novel insights into male-mediated processes, especially where the contribution of the sexes may differ.

Sodium fluoroacetate, commonly referred to as 1080, is a pesticide heavily used to control vertebrate pests. The development of tolerance to this poison by target species is a critical concern raised by its intensive use. Tolerance to 1080 is common amongst many native vertebrates in south-west Western Australia and is thought to be the result of a long period of coevolution with plant species that produce 1080 in their seeds and flowers. Among those vertebrate species tolerant to 1080 exposure is a subspecies of the tammar wallaby (Macropus eugenii). Tammars from Western Australia are tolerant while the subspecies present on Kangaroo Island is susceptible to 1080 exposure. The availability of genetic and genomic information, combined with a distinct difference in tolerance to 1080 between subspecies, makes the tammar wallaby an ideal species in which to study the genetic basis behind 1080 resistance. To date, research in this area has focussed on a candidate gene approach. Since 1080 inhibits the action of the mitochondrial aconitase enzyme, the aconitase gene ACO2 was considered a prime candidate for involvement in 1080 tolerance. However, sequencing of the full-length ACO2 transcript failed to identify a sequence variant between the two subspecies that would result in an amino acid change in the active site of the enzyme. Future studies will need to take a genome-wide approach to identify the gene(s) responsible for 1080 tolerance.

The cohabitation of the common brushtail possum (Trichosurus vulpecula) with people in urban areas often causes conflict. Basic biological parameters are needed to evaluate potential new management options such as fertility control. This study investigated the biology of an urban brushtail possum population and the effects of Suprelorin contraceptive implants on individual females within that population. Trapping success remained constant over time, with 2.8 ± 0.2 individuals trapped per residential property. Recapture rates for males declined rapidly over time, with only 30% of males recaptured on the same property 12 months after initial capture (n = 30) and no males recaptured after 18 months (compared with female recapture rates of 58% after 18 months, n = 33). These data, combined with the preponderance of males observed within the lower age classes, suggests that male possum turnover is high within urban areas. This may be partially compensated for by the male-bias (1.8 : 1) observed in pouch young. Breeding was seasonal with the main peak of births in autumn, and a secondary smaller peak in spring. Suprelorin contraceptive treatment effectively inhibited reproduction in adult females for a minimum duration of 519 ± 7 (n = 5) and ≥700 ± 20 (n = 5) days after administration of one or two 4.7-mg implants, respectively, with no negative side-effects obvious. The concurrent collection of data on contraceptive efficacy and population-specific life-history parameters provides a unique opportunity to highlight the importance of understanding local population dynamics when evaluating the likely efficacy and implementation of fertility control programs to manage problem wildlife.

The spatial and temporal incidence of possum mortality on roads was monitored in Sydney’s northern suburbs over a two-year period. In total, 217 road surveys were completed, equating to over 17 000 km travelled. Almost 600 possums were observed as road-kill, with common ringtail possums (Pseudocheirus peregrinus) encountered in 87% of surveys and almost three times as often as common brushtail possums (Trichosurus vulpecula) (encountered in 52% of surveys). Roads were classified into three categories based on adjacent landscape attributes, with the road-side environment ranging from suburban housing to continuous sclerophyll forest. Clusters, or ‘hot spots’, for possum road-kill were identified using GIS. Most possum fatalities, and five out of six hot spots, occurred along roads at the bush–urban interface, suggesting high possum movement rates and/or abundance at these sites. Continuous canopy across the road was available along only 4% of the roads surveyed, forcing these arboreal marsupials to cross roads via electricity wires or at ground level, making them vulnerable to collision with vehicles. In an attempt to mitigate the possum road toll, two rope tunnel bridges were erected at canopy level above the most consistent hot spot. Subsequent monitoring of the roads was undertaken for 10 months after erection of the canopy bridge and road-kill numbers declined significantly at the site of the bridges, but also at adjacent sites throughout the study area.

Brushtail possums (Trichosurus vulpecula) have been variously described as endangered, pests, prized native wildlife and, recently, as a potential meat export. This article reports information on the increasing decline of the brushtail possum and on attitudes towards these animals. The ‘fit’ between values and attitudes and prevailing governance arrangements is assessed. While the range of this animal is certainly shrinking, areas do exist where the brushtail possum is present at high or very high densities. It is in these areas of high possum density (some urban areas and certain agricultural regions) that conflicts arise, both over the ‘identity’ of the brushtail possum and as to what would be appropriate management. It is argued that although brushtail possums enjoy significant legal protection, these provisions are treated as a nuisance to be circumvented by many residents in areas where possums are in high abundance. Existing policies on possum management somewhat unhelpfully focus attention on situations where possums are overabundant, thus overshadowing situations where active management of declining possum populations would be appropriate.

High extinction rates and loss of biodiversity is a critical conservation matter. Twenty-two Australian mammal species have become extinct in the last 200 years. Of the 95 mammal species under the EPBC Act, 51 have recovery plans and 15 of these have captive components. Zoo-based programs as part of a recovery plan can ‘buy’ time for critically endangered species. In Australia, programs are established as a result of government recovery plans, though more consultation with the zoo industry in initial development phase is needed. Often by the time the decision is taken to remove individuals from the wild for captive breeding, the source populations are fragmented and small. As zoo-based programs become more successful, issues with space limitations arise. This may be rectified with regular release of individuals or avoidance of maintaining post-reproductive and/or non-reproductive animals long-term. Those involved in recovery efforts should make few assumptions on the captive productivity of species, unless the species has been held before. Success of the captive component of a recovery program can be measured by the number of animals bred for release and the level of genetic diversity retained by the program. Although recovery teams are responsible for strategy development, good communication between parties from an early stage is essential. Where a captive component is needed, a more unified strategy, developed early, should provide our native fauna with a realistic chance of recovery. Zoo-based breeding programs are useful in assisting with the preservation of some Australian fauna, whilst for others they will have limited relevance.