Applying Population Viability Analysis to Inform Genetic Rescue That Preserves Locally Unique Genetic Variation in a Critically Endangered Mammal

Genetic rescue can reduce the extinction risk of inbred populations, but it has the poorly understood risk of ‘genetic swamping’—the replacement of the distinctive variation of the target population. We applied population viability analysis (PVA) to identify translocation rates into the inbred lowland population of Leadbeater’s possum from an outbred highland population that would alleviate inbreeding depression and rapidly reach a target population size (N) while maximising the retention of locally unique neutral genetic variation. Using genomic kinship coefficients to model inbreeding in Vortex, we simulated genetic rescue scenarios that included gene pool mixing with genetically diverse highland possums and increased the N from 35 to 110 within ten years. The PVA predicted that the last remaining population of lowland Leadbeater’s possum will be extinct within 23 years without genetic rescue, and that the carrying capacity at its current range is insufficient to enable recovery, even with genetic rescue. Supplementation rates that rapidly increased population size resulted in higher retention (as opposed to complete loss) of local alleles through alleviation of genetic drift but reduced the frequency of locally unique alleles. Ongoing gene flow and a higher N will facilitate natural selection. Accordingly, we recommend founding a new population of lowland possums in a high-quality habitat, where population growth and natural gene exchange with highland populations are possible. We also recommend ensuring gene flow into the population through natural dispersal and/or frequent translocations of highland individuals. Genetic rescue should be implemented within an adaptive management framework, with post-translocation monitoring data incorporated into the models to make updated predictions.

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.

Feral cat predation on Leadbeater’s possum (Gymobelideus leadbeateri) and observations of arboreal hunting at nest boxes

Feral cats have been identified as a major threat to Australian wildlife; however, their impacts on the critically endangered Leadbeater’s possum (Gymobelideus leadbeateri) are unknown. Here, we describe camera trap observations of a feral cat hunting at nest boxes occupied by Leadbeater’s possum. Seven feral cats were subsequently captured within the surrounding area: two had Leadbeater’s possum remains in their stomachs. The prevalence of cat predation on this species, particularly at nest boxes, and how this can be mitigated warrants further investigation.

The marked flooding tolerance of seedlings of a threatened swamp gum: implications for the restoration of critical wetland forests

Wetland forests home to the last remaining wild populations of the helmeted honeyeater and lowland Leadbeater’s possum are under threat from tree dieback and a lack of natural regeneration, putatively the result of an altered hydrological regime. To restore these critical wetland forests, a better understanding of the flooding tolerance of the seedlings of the dominant tree species, Eucalyptus camphora subsp. humeana L.A.S.Johnson & K.D.Hill, is essential. I tested the effect of flooding on the establishment and growth of E. camphora seedlings in three nursery-based experiments. These experiments involved E. camphora seedlings of different ages (1, 3, and 8 months old) being subjected to different depths and durations (up to 12 months) of flooding. Eucalyptus camphora seedlings were able to survive and grow while flooded for 12 months as long as they were emergent. However, flooding negatively affected the growth of E. camphora seedlings, with these effects increasing with increasing depth and duration of flooding, and decreasing seedling age. The ability of E. camphora seedlings to survive prolonged shallow flooding is considerable, an ability enabled by its rapid and extensive production of aerenchyma tissue and stem-borne adventitious roots under flooded conditions. Nonetheless, conditions for E. camphora seedling establishment and growth are likely to improve with reduced flooding, with an absence of flooding during its growth period (early spring–late summer) most favourable.