Understanding the Past to Preserve the Future: Genomic Insights Into the Conservation Management of a Critically Endangered Waterbird.

To ensure the success of genetic rescue, we must minimise the potential negative effects of outbreeding depression that may arise from selecting source populations. The difficulty in assessing the likelihood of outbreeding depression has hindered its consideration in endangered species conservation. However, genomic research offers feasible indications. Here, we conduct conservation genomic analyses on the East Asian (EA) population and the relict Western/Central Asian (WCA) population of the critically endangered Siberian crane (Leucogeranus leucogeranus). We aim to assess genetic rescue's potential advantages and disadvantages between the two populations. Our analysis shows genomic evidence of limited genetic differentiation between them. The persistent decline in population size due to historical climatic oscillations leads to a decrease in genetic diversity and an increase in inbreeding. The WCA population has excessive deleterious homozygous mutations than the EA population, suggesting suffering from inbreeding depression resulting from less effective purifying selection. Forward simulations support the increase in genetic load due to elevated levels of inbreeding compromises fitness during population collapse. We strongly recommend an urgent genetic rescue for the WCA population through population supplementation from the EA population. However, the continuous monitoring of fitness outcomes is required through captive breeding. This work provides useful insights into the genetic management of a critically endangered species and emphasises the importance of evaluating the likelihood of outbreeding depression through genomic approaches.