Plethora of New Marsupial Genomes Informs Our Knowledge of Marsupial MHC Class II

The major histocompatibility complex (MHC) plays a vital role in the vertebrate immune system due to its role in infection, disease and autoimmunity, or recognition of "self". The marsupial MHC class II genes show divergence from eutherian MHC class II genes and are a unique taxon of therian mammals that give birth to altricial and immunologically naive young providing an opportune study system for investigating evolution of the immune system. Additionally, the MHC in marsupials has been implicated in disease associations, including susceptibility to Chlamydia pecorum infection in koalas. Due to the complexity of the gene family, automated annotation is not possible so here we manually annotate 384 class II MHC genes in 29 marsupial species. We find losses of key components of the marsupial MHC repertoire in the Dasyuromorphia order and the Pseudochiridae family. We perform PGLS analysis to show the gene losses we find are true gene losses and not artifacts of unresolved genome assembly. We investigate the associations between the number of loci and life history traits, including lifespan and reproductive output in lineages of marsupials and hypothesize that gene loss may be linked to the energetic cost and tradeoffs associated with pregnancy and reproduction. We found support for litter size being a significant predictor of the number of DBA and DBB loci, indicating a tradeoff between the energetic requirements of immunity and reproduction. Additionally, we highlight the increased susceptibility of Dasyuridae species to neoplasia and a potential link to MHC gene loss. Finally, these annotations provide a valuable resource to the immunogenetics research community to move forward and further investigate diversity in MHC genes in marsupials.

Going to ground: implications of ground use for the conservation of an arboreal marsupial

On the basis of previous observations, the critically endangered western ringtail possum (Pseudocheirus occidentalis) has been described as strictly arboreal. Using motion-sensing cameras placed in bushland remnants and residential gardens, we demonstrate that the species uses the ground during its nocturnally active period. To acknowledge that ground use may make the species more susceptible to terrestrial predators than previously thought, we propose that the species should not be described as ‘strictly’ arboreal.

Use of urban bushland remnants by the western ringtail possum (Pseudocheirus occidentalis): short-term home-range size and habitat use in Albany, Western Australia

Management of wildlife in habitats fragmented by urbanisation requires an understanding of a species’ habitat use. Known populations of the critically endangered western ringtail possum (Pseudocheirus occidentalis) are largely restricted to bushland remnants in rapidly urbanising areas of south-western Australia. Habitat use is thought to be driven by nutritional content, structure and connectivity of canopy vegetation. At the southernmost extent of the species’ range, habitat use is largely unknown, although it is expected to be different from previous descriptions due to differences in vegetation characteristics. We used VHF and global positioning system tracking collars to determine short-term home-range size, diurnal refuge use and night-time tree use of western ringtail possums in bushland remnants within Albany City. Possums had small home ranges (0.88 ha) that were negatively correlated with percentage canopy cover; used a variety of daytime refuges (predominantly dreys); and preferentially utilised marri (Corymbia calophylla) and jarrah (Eucalyptus marginata) at night. These results confirm that differences in habitat use among populations exist and suggests that the species is reasonably flexible in its use of habitat. Management of western ringtail possums needs to be population specific and will benefit from further examination of habitat use in the variety of occupied habitats.

Factors affecting the detection of possums by spotlighting in Western Australia

This paper describes how environmental factors, survey method procedures and differences in forest structure resulting from logging relate to the detection of koomal (common brushtail possum, Trichosurus vulpecula hypoleucus) and ngwayir (western ringtail possum, Pseudocheirus occidentalis). A total of 169 vehicle-based spotlight surveys of possums within native jarrah (Eucalyptus marginata) forest was conducted on three transects over eight years (1996–2003). Up to 5.7 koomal and up to 3.3 ngwayir were detected per kilometre per transect side. Only one ngwayir was detected during the eight surveys conducted between 2001 and 2003. More koomal were seen in spring and autumn (i.e. September–November and March–May respectively) and more ngwayir were seen between October and April. Although surveys were not conducted on very rainy or excessively windy nights, fewer possums were nonetheless seen on nights following rainy days and on cold nights. Cloud cover also affected sightings of koomal. The time taken to complete the surveys increased in conjunction with the number of possums detected, on account of the time required to record data. The importance of standardising travelling speed also is emphasised. Possum spotlight counts differed between recently logged and unlogged areas. However, these findings were not supported by complementary koomal abundance estimates derived from trapping, suggesting that vegetation structure may affect detectability. Factors such as the lunar cycle, wind speed and survey start time after sunset did not significantly affect detection rates of either species. On the basis of these findings, specific survey conditions can be selected to improve spotlight detection efficiency.