Leadbeater's Possum Research Articles

Management lessons from a long‐term captive‐breeding program for a critically endangered species, Leadbeater's possum, Gymnobelideus leadbeateri

AbstractLeadbeater's possums (Gymnobelideus leadbeateri) are a critically endangered marsupial found in a restricted area of cold, wet forest in South‐Eastern Australia. The majority of Leadbeater's possums inhabit highland forest, with one outlying lowland population. In 2012, a breeding program was established for the lowland Leadbeater's possums when this genetically distinct population faced imminent extinction. Successful reproduction by highland Leadbeater's possums in the international zoo‐based population between 1970 and 2010 led to the widespread belief that the species bred readily in captivity. Lowland possums have not bred in the 2012–2021 contemporary captive conservation breeding program. This study reviewed the historic captive‐breeding data and found that of the 84% (162/194) that reached reproductive maturity; 37% of males (n = 30) and 39.5% of females (n = 32) bred, and this success was highly skewed towards a subset of highly fecund individuals (14% of females and 15% of males produced 75% and 80% of all offspring). Although lack of reproductive output in the captive lowland animals could be explained if age at mortality was lower than that of highlands possums, comparison of the longevity of highland and lowland animals had no significant difference. Conservation objectives that specify how captive breeding may support in situ recovery of wild populations are integral to the success of captive programs. A lack of reflective analysis of past husbandry records allowed misconceptions of success and approaches implemented in the management of the breeding program, reducing the benefits for the conservation of this high profile threatened species. This case study provides a lesson for the management of conservation breeding programs and illustrates the importance of well‐defined conservation objectives, integration of in situ and ex situ strategies, and the importance of objective, systematic and timely analysis of available evidence to inform management objectives and improve conservation outcomes in real time.

A RETROSPECTIVE ANALYSIS OF MORBIDITY AND MORTALITY IN THE CAPTIVE LEADBEATER'S POSSUM (GYMNOBELIDEUS LEADBEATERI) POPULATION FROM 1970 TO 2021.

The Leadbeater's possum (Gymnobelideus leadbeateri) is a critically endangered nocturnal marsupial with a restricted range in the Central Highlands of Victoria, Australia. There are two genetically distinct populations divided by location: highland and lowland. Lowland possums exist in one remnant swamp forest and entered captivity in 2012 when ∼60 individuals remained. Today, with less than 20 lowland individuals remaining, any information that informs the yet-unsuccessful breeding program is critical. This study encompasses a retrospective analysis of the causes of mortality and significant histological lesions in captive highland and lowland individuals across seven institutions internationally from 1970 to 2021. During this time, 245 possums lived in captivity. Postmortem records exist for 99 animals, including 349 histopathology diagnoses from 80 reports and 264 gross necropsy diagnoses from 78 reports. Diagnoses were assigned into two categories based on the importance to the individual (causing death or morbidity to a single animal [n = 194]), or importance to the wider population (causing death or morbidity to more than one animal or was related to reproduction [n = 155]). Individual animals had multiple diagnoses, which were tallied as individual data points. Renal disease was diagnosed 57 times; the most common finding was chronic nephropathy (43/57). Cardiovascular disease was diagnosed 33 times; atherosclerosis associated with obesity was common (n = 10/33). Both categories suggest causal association with captive husbandry but elicit no comment on the lack of success of the breeding program. Reproductive disease was diagnosed 36 times in 24 animals (14 females and 10 males). In females, 11 cases of uterine inflammation and associated clinical signs were associated with ascending infection or neoplasia. Of the seven lowland male possums with mortality data, five were infertile (azoospermia or testicular atrophy). More investigation into the reproductive health of this population is indicated to understand the lack of success in the current breeding program.

Mitigating the effect of linear infrastructure on arboreal mammals in dense forest: A canopy bridge trial

SummaryRoads and other linear infrastructure create treeless gaps that can limit the movement of non‐flying, arboreal animals. These negative effects are particularly strong in dense forests, where even narrow infrastructure corridors represent a significant change in habitat structure. Artificial canopy bridges are an increasingly common approach to mitigating the barrier effect of roads and other linear infrastructure on the movement of arboreal mammals; however, questions remain about the success of various designs for different species. Here we conduct an experimental evaluation of the response of a critically endangered possum, Leadbeater's Possum (Gymnobelideus leadbeateri), to two artificial canopy bridge designs: single‐rope bridges and ladder bridges. We found that both bridges were used by Leadbeater's Possum and five other species of arboreal marsupial to cross narrow, forestry roads. However, Leadbeater's Possums crossed ladder bridges 13 times more often than the single‐rope design (average of 564.5 and 41.75 crossings per design respectively). Radiotelemetry conducted on four Leadbeater's Possums prior to bridge installation detected no road crossings, providing preliminary evidence that the bridges improved cross‐road movement. Ladder bridges appear to be the better design choice for a wider range of arboreal marsupials as they were used more frequently, offer greater stability, and provide better predator avoidance than single‐rope designs.

Molecular detection of two new putative species of gammaherpesvirus in petaurid possums.

A molecular survey of herpesviruses in Australian native mammals was conducted, spanning 260 individuals from 27 species. Among the herpesviruses detected, a putative new gammaherpesvirus species was detected in the yellow-bellied glider (Petaurus australis), and another in the critically endangered Leadbeater's possum (Gymnobelideus leadbeateri). In addition, the known host range of the putative species macropodid gammaherpesvirus 3 (MaHV-3) is herein extended to the western grey kangaroo (Macropus fuliginosus). These findings expand our understanding of herpesviruses in Australian mammals and may inform biosecurity protocols for captive and translocated populations.

An assessment of ectoparasites across highland and lowland populations of Leadbeater's possum (Gymnobelideus leadbeateri): Implications for genetic rescue translocations.

Leadbeater's possum (Gymnobelideus leadbeateri) is a nocturnal arboreal marsupial with a restricted range centered on the Victorian Central Highlands, south-eastern Australia. Most populations inhabit wet montane ash forest and subalpine woodland, with one notable exception - a small, outlying and genetically-distinct lowland population inhabiting swamp forest at Yellingbo, Victoria. The species has been listed as critically endangered since 2015. Translocations are the mainstay of critical genetic rescue and this study explores the ectoparasites that are ‘along for the ride’ during translocation activities. Ectoparasites (133 fleas, 15 ticks and 76 mites) were collected opportunistically from 24 Leadbeater's possum colonies during population monitoring and genetic sampling across the lowland and highland populations. The composition of the flea assemblage varied by habitat type. Significantly greater numbers of the general marsupial fleas Acanthopsylla r. rothschildii. and Choristopsylla tristis (as a proportion of total flea numbers) were detected in lowland habitats, compared to highland habitats (Fishers exact test, P < 0.0001). Two host-specific flea species, Stephanocircus domrowi and Wurunjerria warnekei were detected only on possums in highland habitats. As a proportion of total fleas this was significantly different to possums in lowland habitats (Fisher's exact test, P = 0.0042 and P < 0.0001, respectively). Wurunjerria warnekei was suspected to be extinct prior to this study. Ticks (Ixodes tasmanii, n = 15) and mites (Haemdoelaps cleptus, n = 47 and H. anticlea, n = 29) have been identified in Leadbeater's possums historically. The possible causes of the different flea assemblages may be environmental/climatic, or due to the historic geographic division between highland and lowland animals. The planned translocations of highland individuals to lowland habitats will expose lowland individuals to novel species of previously exclusively highland fleas with unknown indirect consequences, thus careful monitoring will be required to manage any potential risks.

Using species distribution models and decision tools to direct surveys and identify potential translocation sites for a critically endangered species

AbstractAimOccurrence records for cryptic species are typically limited or highly uncertain, leaving their distributions poorly resolved and hampering conservation. This can apply to well‐studied species, and increased survey effort and/or novel methods are required to improve distribution data. Here, we paired species distribution modelling (SDM) with decision tools to direct surveys for the critically endangered Leadbeater's possum (Gymnobelideus leadbeateri) outside its current restricted range. We also assessed survey areas for their suitability to host translocations.LocationVictoria, Australia.MethodWe used both recent and historic records (now out of range and spatially uncertain) of Leadbeater's possum to build SDMs using MaxEnt. The SDMs informed an initial multi‐criteria decision analysis (MCDA) that enabled prioritization of 80 survey sites across seven forest patches (13–145 km outside the known range), which we surveyed using camera traps. Site and vegetation data were used in a post‐survey MCDA to rank their potential translocation suitability.ResultsThe SDM predictions were consistent with the species’ ecology, identifying cold areas with high rainfall that had not recently burnt as suitable. The spatial uncertainty of records did not exert a strong influence on either model predictions or the ranking of patches for surveys. Camera trap surveys yielded records of 19 native species, with Leadbeater's possum detected in only one survey patch, 13 km outside of its previously known range. The post‐survey MCDA identified three forest patches as potentially suitable for conservation translocations, and these priorities were not sensitive to the decision criteria used.Main conclusionsThe approach outlined here prioritized survey effort over a large area, resulting in detection of Leadbeater's possum in one new patch. The potential translocation sites identified could present an important risk‐spreading measure for the species given the threat posed by bushfire. Combining SDMs and decision tools can help target surveys and guide subsequent conservation strategies.

Detection of Breinlia sp. (Nematoda) in the Leadbeater's possum (Gymnobelideus leadbeateri).

The Leadbeater's possum (Gymnobelideus leadbeateri) is a critically endangered marsupial in south-eastern Australia. Among other conservation efforts, free-ranging animals in the two remaining geographically separate populations (highland and lowland) have been extensively studied; however, little is known about their health and mortality. Although some wild populations are frequently monitored, cadavers are rarely recovered for post mortem examination. In June 2019, a recently deceased, wild, adult male lowland Leadbeater's possum was collected from a nest box and a comprehensive post mortem examination was conducted. Microfilariae of a filarioid nematode were observed in testes, liver, lung and skin samples in tissue impression smears and upon histopathological examination. No gross or histological changes were seen associated with the parasites, except for a focal area of tissue damage in the skin, suggesting that the possum is a natural host. Using a PCR-coupled sequencing method the filarioid was identified as a species of Breinlia. Species of Breinlia occur in other Australian marsupials and rodents.

The vegetation structure and condition of contracting lowland habitat for Leadbeater's possum (Gymnobelideus leadbeateri)

Lowland Leadbeater’s possums are on a trajectory to extinction, with fewer than 40 individuals surviving in the wild. Quantification of the vegetation characteristics of their occupied habitat is urgently needed to inform strategies to conserve this genetically distinct population. We surveyed the canopy and midstorey vegetation at all remaining (nine) occupied territories and eleven abandoned territories in lowland swamp forest at the Yellingbo Nature Conservation Reserve. For each territory we quantified canopy and midstorey stem density, basal area (total and live) and vegetation condition (percentage live basal area, tree crown vigour and plant area index) within a 50-m radius of known den locations. The canopy at all locations was dominated by mountain swamp gum (Eucalyptus camphora), with most occupied sites supporting dense midstorey dominated by paperbarks, either Melaleuca squarrosa or Melaleuca ericifolia. Occupied territories had higher stem densities and better vegetation condition than abandoned territories. Stem density alone was able to predict occupancy vis-à-vis abandoned sites with a high (80%) degree of accuracy. Lowland Leadbeater’s possums occupy swamp forests characterised by high stem density, particularly in the midstorey, structural complexity and healthy vegetation. These findings can help guide habitat restoration and translocation projects currently underway to expand the area of lowland habitat for this critically endangered species.

Accounting for cryptic population substructure enhances detection of inbreeding depression with genomic inbreeding coefficients: an example from a critically endangered marsupial.

Characterizing inbreeding depression in wildlife populations can be critical to their conservation. Coefficients of individual inbreeding can be estimated from genome-wide marker data. The degree to which sensitivity of inbreeding coefficients to population genetic substructure alters estimates of inbreeding depression in wild populations is not well understood. Using generalized linear models, we tested the power of two frequently used inbreeding coefficients that are calculated from genome-wide SNP markers, FH and F^III , to predict four fitness traits estimated over two decades in an isolated population of the critically endangered Leadbeater's possum. FH estimates inbreeding as excess observed homozygotes relative to equilibrium expectations, whereas F^III quantifies allelic similarity between the gametes that formed an individual, and upweights rare homozygotes. We estimated FH and F^III from 1,575 genome-wide SNP loci in individuals with fitness trait data (N=179-237 per trait), and computed revised coefficients, FHby group and F^IIIby group , adjusted for population genetic substructure by calculating them separately within two different genetic groups of individuals identified in the population. Using FH or F^III in the models, inbreeding depression was detected for survival to sexual maturity, longevity and whether individuals bred during their lifetime. F^IIIby group (but not FHby group ) additionally revealed significant inbreeding depression for lifetime reproductive output (total offspring assigned to each individual). Estimates of numbers of lethal equivalents indicated substantial inbreeding load, but differing between inbreeding estimators. Inbreeding depression, declining population size, and low and declining genetic diversity suggest that genetic rescue may assist in preventing extinction of this unique Leadbeater's possum population.

The adequacy of Victoria's protected areas for conserving its forest‐dependent fauna

AbstractNetworks of protected areas are a key component of efforts to conserve biodiversity. However, there are concerns about an uncritical focus on the percentage area of reserves without an assessment of how well formal reserves are actually protecting biodiversity. In response, we completed a spatial analysis of the formal reserve system in the Australian state of Victoria. We quantified how well the reserve system captured a crude surrogate for vegetation communities (viz: Ecological Vegetation Classes) as well as distribution models for an array of threatened forest‐dependent species. We found evidence of a high degree of overlap between areas subject to intensive forestry (clearcutting) operations and the modelled distribution of a suite of forest‐dependent species. A key outcome of our study was that areas around sites subject to past logging as well as new areas proposed for logging under the Timber Release Plan in Victoria had significantly higher values for threatened forest‐dependent species (as determined by habitat distribution models) than areas that had not been logged. We found significant differences in the spatial characteristics of the dedicated reserve systems and informal protected area networks, with the latter featuring much of its area close to a tenure boundary where logging occurs. Our empirical analyses demonstrating the impacts of ongoing logging operations on areas with high environmental suitability for threatened species have important implications. In particular, the current reserve system is inadequate for a suite of forest‐dependent taxa, including critically endangered Leadbeater's Possum (Gymnobelideus leadbeateri) and the vulnerable Greater Glider (Petauroides volans). This suggests a high degree of conflict between areas of high value for conservation and areas targeted for wood production.

Range extension of Leadbeater's possum (Gymnobelideus leadbeateri)

We report spotlight and camera-trap observations of Leadbeater’s possum (Gymnobelideus leadbeateri) at six locations up to 15km east of its described range. Half of our records occurred in fire-affected, mixed-species forest, with a tree species and seral stage composition that differs markedly from its predominant habitat: late-mature forests dominated by Eucalyptus regnans, E. delegatensis and E. nitens.

Failing to conserve Leadbeater's Possum and its Mountain Ash forest habitat

ABSTRACT The conservation of the Critically Endangered Leadbeater's Possum Gymnobelideus leadbeateri in Victoria's Mountain Ash Eucalyptus regnans forests is one of the most controversial native mammal conservation issues in Australia. Much of the controversy results from long-running conflicts between the demands of the native forest logging industry and associated impacts on Leadbeater's Possum and its Mountain Ash forest habitat. Here we argue that despite a legislative obligation to protect Leadbeater's Possum and some limited recent improvements in management, conservation efforts for the species have gone backwards over the past decade. The key problems we identify include that the Victorian Government has: (1) maintained levels of wood production that are too high given the amount of the forest estate that was burned in 2009, (2) failed to substitute clearfell logging practices with more ecologically-sensitive Variable Retention Harvesting Systems, (3) ignored the science (including by its own rese...

Inter-den tree movements by Leadbeater's Possum

ABSTRACT Many species of arboreal marsupials move regularly between den sites in hollow-bearing trees. We show, based on short-term radio-tracking data, that the Critically Endangered Leadbeater's Possum (Gymnobelideus leadbeateri) can move 100 m (and sometimes up to 600 m) between den sites in hollow-bearing trees. These movement data have significant implications for the design of buffers of unlogged forest to protect colonies of Leadbeater's Possum as well as for crude estimates of the species' population size.

The use of call imitation to establish territory occupancy by Leadbeater's possum (Gymnobelideus leadbeateri)

Leadbeater’s possum (Gymnobelideus leadbeateri) is a cryptic, endangered species that is notoriously difficult to detect using conventional mammal survey methods. However, the imitation of the species’ social contact and/or alarm calls has previously been found to attract resident animals. Call imitation was employed as a secondary survey method to confirm ongoing site occupancy by Leadbeater’s possum at Yellingbo Nature Conservation Reserve. All call imitation reported here was conducted at sites currently or previously known to be occupied by particular family groups. The results indicate that the method has considerable promise as a tool to facilitate broad-scale surveys targeting this species. However, ‘false negatives’ did occur during the surveys at Yellingbo, highlighting that additional testing is required to adequately characterise the species’ response patterns, in particular variation in the response rate in occupied territories and the distance over which animals will respond. A detailed understanding of these factors is essential to permit reliable interpretation of survey findings.

Continental‐Scale Governance and the Hastening of Loss of Australia's Biodiversity

Against a global backdrop of rapid environmental change, conserving biodiversity poses one of the biggest and most important challenges to society. For this reason, systems of nature reserves have never been more important. Protected areas are under threat in many parts of the world (Mascia & Pailler 2011), but the weakening of protected areas in a rich, developed country with a global reputation for conservation leadership (Harrison 2006) is particularly alarming (Ritchie 2013). Consequently, we are concerned about the recent spate of substantial policy, legislative, and management changes being made by three of six Australian state governments for exploitative uses of national parks—actions that could affect much of Australia and have negative effects on biodiversity.

Leadbeater's Possum – May Meeting Talk by Raymond Gibson

Leadbeater's Possum – May Meeting Talk by Raymond Gibson

Can Individual and Social Patterns of Resource Use Buffer Animal Populations against Resource Decline?

Species in many ecosystems are facing declines of key resources. If we are to understand and predict the effects of resource loss on natural populations, we need to understand whether and how the way animals use resources changes under resource decline. We investigated how the abundance of arboreal marsupials varies in response to a critical resource, hollow-bearing trees. Principally, we asked what mechanisms mediate the relationship between resources and abundance? Do animals use a greater or smaller proportion of the remaining resource, and is there a change in cooperative resource use (den sharing), as the availability of hollow trees declines? Analyses of data from 160 sites surveyed from 1997 to 2007 showed that hollow tree availability was positively associated with abundance of the mountain brushtail possum, the agile antechinus and the greater glider. The abundance of Leadbeater’s possum was primarily influenced by forest age. Notably, the relationship between abundance and hollow tree availability was significantly less than 1∶1 for all species. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low. The resource-sharing response was weaker and inconsistent among species. Two species, the mountain brushtail possum and the agile antechinus, showed significant but contrasting relationships between the number of animals per occupied tree and hollow tree abundance. The discrepancies between the species can be explained partly by differences in several aspects of the species’ biology, including body size, types of hollows used and social behaviour as it relates to hollow use. Our results show that individual and social aspects of resource use are not always static in response to resource availability and support the need to account for dynamic resource use patterns in predictive models of animal distribution and abundance.

Principles and practices for biodiversity conservation and restoration forestry: a 30 year case study on the Victorian montane ash forests and the critically endangered Leadbeater's Possum

We present a detailed case study of conservation and restoration of the Australian arboreal marsupial Leadbeater's Possum (Gymnobelideus leadbeateri) and its Mountain Ash forest habitat to illustrate the important intersection between forest restoration principles and the general principles for forest biodiversity conservation. Mountain Ash forests have been extensively modified through a century of intensive logging, recurrent wildfires and post-fire salvage logging. These disturbances have led to a reduction in old growth forest to 1/30th-1/60th of the extent of historical levels, a rapid collapse followed by a prolonged (≯30-year) shortage of populations of hollow-bearing trees throughout the Mountain Ash forests (which are critical habitat elements for many species of cavity-dependent vertebrates), and an increased risk of re-burning of landscapes dominated by young, regrowth forest. The consequences of the severe decline and consequent ‘temporary extinction’ of large old trees will be the potential g...

Population genetic analysis reveals a long‐term decline of a threatened endemic Australian marsupial

Since European colonization, Leadbeater's possum (Gymnobelideus leadbeateri) has declined across its range to the point where it is now only patchily distributed within the montane ash forests of the Central Highlands of Victoria. The loss of large hollow-bearing trees coupled with inadequate recruitment of mature ash forest has been predicted to result in a reduction in population size of up to 90% by 2020. Furthermore, bioclimatic analyses have suggested additional reductions in the species' distribution under a variety of climate change scenarios. Using a panel of 15 highly resolving microsatellite markers and mitochondrial control region sequence data, we infer past and present gene flow. Populations in the northern part of the core range were highly admixed, and showed no signs of either current or historical barriers to gene flow. A marginal, isolated and inbred population at Yellingbo was highly genetically differentiated, both in terms of current and historic genetic structure. Sequence data confirmed the conclusions from earlier genetic simulation studies that the Yellingbo population has been isolated from the rest of the species range since before European-induced changes to the montane landscape, and formed part of a larger genetic unit that is now otherwise extinct. Historic loss of maternal lineages in the Central Highlands of Victoria was detected despite signals of immigration, indicating population declines that most probably coincided with changes in climate at the end of the Pleistocene. Given ongoing habitat loss and the recent (February 2009) wildfire in the Central Highlands, we forecast (potentially extensive) demographic declines, in line with predicted range reductions under climate change scenarios.

Isolated remnant or recent introduction? Estimating the provenance of Yellingbo Leadbeater's possums by genetic analysis and bottleneck simulation

Effective conservation management requires that genetically divergent populations potentially harbouring important local adaptations be identified and maintained as separate management units. In the case of the endangered Australian Leadbeater's possum (Gymnobelideus leadbeateri), an arboreal marsupial endemic to Victoria, uncertainty over the evolutionary origin of a potentially important extant wild population recently discovered in atypical habitat (lowland swamp) at Yellingbo is hampering such efforts. The population is rumoured to be a recent introduction. Microsatellite allele frequencies at Yellingbo differed substantially from those in sampled populations in montane ash forest (F(ST) between 0.23 and 0.36), and Bayesian clustering analyses of genotypes strongly separated them (K = 2). We conducted a suite of bottlenecking tests which all indicated that Yellingbo had undergone a recent reduction in size. The extent to which the distinctiveness of Yellingbo animals might be expected solely through bottlenecking associated with a recent introduction, was tested by simulating population-history scenarios seeded with genotypes from candidate wild and captive sources. No bottleneck scenario reproduced anything approaching the genetic distinction of the Yellingbo population, with all STRUCTURE analyses placing Yellingbo in a separate cluster to simulated populations (K = 2, minimum F(ST) = 0.13). These results suggest that Yellingbo does not share recent ancestry with other extant populations and instead may be a remnant of an otherwise extinct gene pool. Importantly, this may include genes involved in adaptation to a lowland swamp environment, substantially adding to the conservation importance of this population, and suggesting that separate management may be prudent until evidence suggests otherwise.