The use of multiple source populations provides a way to maximise genetic variation and reduce the impacts of inbreeding depression in newly established translocated populations. However, there is a risk that individuals from different source populations will not interbreed, leading to population structure and smaller effective population sizes than expected. Here, we investigate the genetic consequences of mixing two isolated, morphologically distinct island populations of boodies (Bettongia lesueur) in a translocation to mainland Australia over three generations. Using 18 microsatellite loci and the mitochondrial D-loop region, we monitored the released animals and their offspring between 2010 and 2013. Despite high levels of divergence between the two source populations (F_ST = 0.42 and ϕ_ST = 0.72), there was clear evidence of interbreeding between animals from different populations. However, interbreeding was non-random, with a significant bias towards crosses between the genetically smaller-sized Barrow Island males and the larger-sized Dorre Island females. This pattern of introgression was opposite to the expectation that male–male competition or female mate choice would favour larger males. This study shows how mixing diverged populations can bolster genetic variation in newly established mammal populations, but the ultimate outcome can be difficult to predict, highlighting the need for continued genetic monitoring to assess the long-term impacts of admixture.

Many Australian mammal species now only occur on islands and fenced mainland havens free from invasive predators. The range of one species, the banded hare-wallaby (Lagostrophus fasciatus), had contracted to two offshore islands in Western Australia. To improve survival, four conservation translocations have been attempted with mixed success, and all occurred in the absence of genetic information. Here, we genotyped seven polymorphic microsatellite markers in two source (Bernier Island and Dorre Island), two historic captive, and two translocated L. fasciatus populations to determine the impact of multiple translocations on genetic diversity. Subsequently, we used population viability analysis (PVA) and gene retention modelling to determine scenarios that will maximise demographic resilience and genetic richness of two new populations that are currently being established. One translocated population (Wadderin) has undergone a genetic bottleneck and lost 8.1% of its source population’s allelic diversity, while the other (Faure Island) may be inbred. We show that founder number is a key parameter when establishing new L. fasciatus populations and 100 founders should lead to high survival probabilities. Our modelling predicts that during periodic droughts, the recovery of source populations will be slower post-harvest, while 75% more animals—about 60 individuals—are required to retain adequate allelic diversity in the translocated population. Our approach demonstrates how genetic data coupled with simulations of stochastic environmental events can address central questions in translocation programmes.

Conservation translocations have become increasingly popular for ‘rewilding’ areas that have lost their native fauna. These multispecies translocations are complex and need to consider the requirements of each individual species as well as the influence of likely interactions among them. The Dirk Hartog Island National Park Ecological Restoration Project, Return to 1616, aspires to restore ecological function to Western Australia’s largest island. Since 2012, pest animals have been eradicated, and conservation translocations of seven fauna species have been undertaken, with a further six planned. Here, we present a synthesis of the innovative approaches undertaken in restoring the former faunal assemblage of Dirk Hartog Island and the key learnings gathered as the project has progressed.

Little is known about the baseline health status of Australia’s native rodents. The resultant knowledge gaps are problematic for wildlife translocations, as assessing disease risk is integral to translocation planning and outcomes. A disease risk analysis was conducted for the conservation translocation of native rodents to Dirk Hartog Island, Western Australia. This analysis resulted in a recommendation for a multidisciplinary project to reduce knowledge gaps about the health status of Shark Bay mice (Pseudomys gouldii) and greater-stick-nest rats (Leporillus conditor). Between 2021 and 2022, 130 Shark Bay mice and 122 greater stick-nest rats were translocated to Dirk Hartog Island. Mucosal swabs, whole blood, faeces, and ectoparasites were collected from a subset of these individuals. Molecular testing for four infectious agents was performed, parasite burdens and haematological parameters were examined, and relationships between these variables, health metrics and post-translocation short-term survival were assessed. Necropsies with routine histological assessment on translocation mortalities were performed where feasible. Several indicators of non-infectious factors contributing to morbidity or mortality were found, highlighting the need to iteratively evaluate translocation strategies. There was also an apparent absence of some host-specific parasites, suggesting that active approaches to parasite conservation during translocations should be considered. Molecular evidence of herpesviruses, a paramyxovirus, Bartonella sp., Trypanosoma sp. and Mycoplasma spp. were detected among the translocated animals. Although not associated with morbidity or short-term mortality in this study, the disease potential of these agents is still present. Overall, these results contribute important new data on health baselines for both species, which will assist in informing future conservation planning.