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Letting black rhinos roam freely may be the best way to save them from the hidden genetic dangers of inbreeding, according to a new study, the first to look at the whole genomes of these critically endangered mammals from populations in Tanzania.

The new research, published in the Proceedings of the National Academy of Sciences (PNAS), was a collaboration between the Tanzania National Parks Authority (TANAPA), Tanzania Wildlife Research Institute (TAWARI) and researchers at the University of Glasgow.

Currently, in most parts of their range, rhinos exist in enclosed sanctuaries to protect them from their most serious threat: poaching for their horns. This means that there is a risk of inbreeding unless new animals are introduced into the closed populations.

The study, which focused on native black rhino in Tanzania, revealed that supporting the natural movement of rhinos across their habitat is better for the species' overall health and survival, than relying on costly and difficult translocations of new animals to breed with wild populations.

Through whole genome sequencing, the researchers found that while individuals with a translocated parent showed less inbreeding than native populations, their genomes showed more negative mutations. Surprisingly, they found that rhinos which were able to roam freely, and breed with other local populations, showed some of the same benefits in terms of reducing inbreeding but strong evidence that the most serious mutations had been purged by natural selection.

The research team say the study results highlight the potential trade-off between reducing inbreeding and the hidden genetic risks of moving animals between populations that have been adapted to different conditions.

Carrying out this study required close collaboration between researchers in Glasgow and colleagues working directly with rhino populations in Tanzania. To assist with tracking individuals, each adult rhino in the Serengeti population has their ears notched in a unique pattern. The study team worked with TANAPA and TAWIRI to extract DNA from these samples, along with blood taken during standard veterinary procedures. Samples were then brought to the University of Glasgow where the whole genome of 21 individual rhinos was sequenced and analysed.

Dr Ronald Mellya, first author, who undertook the study while carrying out his PhD at the University of Glasgow, said: “Black rhino populations have survived several historic bottlenecks across Africa, most recently due to poaching. Often these populations have been reduced to just a few individuals which requires focused conservation and research efforts to ensure their recovery.

“Whole genome sequencing provides a powerful tool for us to gain greater insights about how to manage these populations better.”

Anubhab Khan, a lead author of the study, from the University of Glasgow’s School of Biodiversity, One Health & Veterinary Medicine, said: “The study uses cutting edge techniques for analysing sequences of whole genomes of individual rhinos. The method allowed us to study billions of base pairs of DNA and the approach of dividing the population into various cohorts helped us gain unprecedented insights to understand the effects of translocation and natural dispersal.”

Northern Tanzania remains one of the last strongholds for wild populations of black rhino in the world. Instead of relying on fences, elite teams of dedicated rangers provide 24-hour protection to Tanzania’s black rhino population, particularly in the Greater Serengeti-Mara Ecosystem where these shy, yet majestic animals move between conservation areas such as the Serengeti National Park, the Ngorongoro Conservation Area, Grumeti, and Maswa and even across the international boundary between Tanzania and Kenya.

Before this study, the approach was to manage the rhinos in Intensive Protection Zones, where wardens monitor individuals and prevent them from moving out of particular safe zones, resulting in keeping small and isolated sub-populations apart.

To maintain their numbers, and prevent too much inbreeding, the Serengeti population has been supplemented by individuals translocated from other places including South Africa, European zoos or Kenya. However, translocations are not without difficulty. They are known to be expensive – in terms of finances and animal welfare – and animals raised in captive environments sometimes do not adjust well to wild conditions so rates of survival can be low.

The results from the study suggest that, where it is possible, opening natural corridors for rhinos to naturally disperse and roam free within an ecosystem could be less costly than relying only on such translocations. Indeed, the research team say, in the Serengeti ecosystem, the costs of employing more rhino wardens to protect the natural corridors within the ecosystem could be less than a single translocation.

Professor Barbara Mable, Professor of Evolutionary Genetics at the University of Glasgow, and a lead author of the study, said: “Translocations can bring in new genetic variants, but they may also introduce hidden genetic risks that build up in captivity. Our findings suggest that maintaining habitat corridors to allow rhinos to move naturally might be a more sustainable solution.”

Philbert Ngoti, Tanzania’s Rhino Coordinator and co-author of the study, said: “Translocations are often very expensive and risky operations. While they are a useful approach, this research has shown that rhinos do best when they have space to live and move in natural ways.”

TANAPA’s Deputy Conservation Commissioner Massana Mwishawa, who oversees the protection of many of these areas, said: “What we see from this research is that supporting the natural movement of rhino across these landscapes is key to the species' survival, rather than relying solely on translocations.”

Dr David Balfour, the Chair of the IUCN Rhino Specialist Group, said: “This research comes at a time when the continental populations of African rhinos no longer occupy their natural distribution range but rather are site-bound and fragmented in relatively small populations. As conservationists debate the best strategies for managing species like the rhino across Africa in the wild we need the kinds of insights that emerge from this research to improve our interventions. Captive populations can play a short term role in conservation but should not be seen as a long-term solution. The best thing for rhinos is the protection and connection of rhino habitat at scale.”

The study, ‘Natural dispersal is better than translocation for reducing risks of inbreeding depression in eastern black rhinoceros (Diceros bicornis michaeli)’ is published in PNAS.

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Enquiries: ali.howard@glasgow.ac.uk or elizabeth.mcmeekin@glasgow.ac.uk

First published: 4 June 2025