A growing body of empirical studies on critically endangered species 4, 5 indicates that small populations are often exposed to genomic erosion, which reduces species viability via loss of genetic diversity, increase in inbreeding and in genetic load (i.e., decrease in average individual fitness relative to the fittest genotype due to deleterious mutations) through genetic drift 6, 7, 8. Over the past few decades, the role of genetic factors in the long-term viability of small populations has gained considerable attention 2, 3. Small and fragmented populations are vulnerable to several extrinsic and intrinsic threats, such as environmental effects (e.g., disease, habitat destruction), demographic stochasticity and detrimental genetic effects 1. Moreover, we find little evidence for differences in local adaptation among populations, suggesting that future inbreeding depression could potentially be mitigated by assisted gene flow among populations. The currently small population sizes may thus in the near future lead to inbreeding depression.
The populations on Sumatra and Borneo instead show low inbreeding, but high mutational load. We find that the Malay Peninsula population experienced increased inbreeding shortly before extirpation, which possibly was accompanied by purging.
Here, we analyse 5 historical and 16 modern genomes from these populations to investigate the genomic consequences of the recent decline, such as increased inbreeding and mutational load. The Sumatran rhinoceros was widespread in Southeast Asia, but is now restricted to small and isolated populations on Sumatra and Borneo, and most likely extinct on the Malay Peninsula. Small populations are often exposed to high inbreeding and mutational load that can increase the risk of extinction. Nature Communications volume 12, Article number: 2393 ( 2021) Genomic insights into the conservation status of the world’s last remaining Sumatran rhinoceros populations
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