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.

Bird pollination is particularly common and widespread in the southern regions of Australia. Despite some eucalypts being heavily frequented by birds, they are usually considered to have a generalist pollination system because of their apparently unspecialised floral morphology. A few species possess protandrous anthers that dehisce within a tightly furled dome of filaments. We hypothesised that this facilitates pollen transport via the brush tongues of lorikeets. Using Eucalyptus leucoxylon F.Muell. and five captive rainbow lorikeets (Trichoglossus hematodus) as a model, we demonstrated that lorikeets remove significant quantities of pollen from flowers with inflexed filaments in a short time (30 min), compared with bagged control flowers (Mann–Whitney U test, Z = 165.4, d.f. = 29, P = 0.008). Some of this pollen is deposited on stigmas by the tongue, which is the organ that most regularly and reliably contacts stigmas. The mean number of pollen grains deposited on stigmas by each bird was as high as 121.2. Adhesive tape contacted by the tongue during foraging removed up to 2104 pollen grains, which was significantly greater than for uncontacted control tape (Mann–Whitney U test, Z = 110, d.f. = 21, P < 0.001). Scanning electron micrograph imaging of a lorikeet tongue showed many pollen grains that had been transferred onto its keratin papillae, which is likely to have contributed to high carryover rates by retaining pollen for a substantial amount of time. Minimal pollen is available for generalist pollination once the filaments unfurl. It appears highly unlikely that insects are able to access pollen from these male-phase flowers and inflexed filaments may therefore fulfil an exclusionary role.

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.

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