The northern white rhinoceroses Najin and Fatu live on the Ol Pejeta Conservancy in Kenya

Ol Pejeta/DPA/TNS/Alamy Live News

There are only two northern white rhinos left on the planet, but the species may be able to recover from the brink of extinction using frozen skin cells from deceased rhinos.

Much of the hope for the future of the northern white rhino (Ceratotherium simum cottoni) has rested on the last surviving members of the subspecies: Fatu and Najin, an infertile mother-daughter pair. But because neither can carry a pregnancy, experts are turning to genetic and reproductive innovation.

That led researchers at the San Diego Zoo Wildlife Alliance in California to look at skin cells taken from 12 different northern white rhinos that are stored in their Frozen Zoo, a repository of genetic material from more than a thousand different species. Using a computer model, they simulated how the subspecies would fare if these rhinos’ genetic material was used to generate sperm and egg cells, which could then be turned into embryos and carried by females of the closely related southern white rhino (Ceratotherium simum simum).

They found that it would be possible to restore the population of northern white rhinos over multiple generations – no Fatu and Najin needed. “The beauty of having this consistent resource of genomes in the Frozen Zoo is that we can continually pull new individuals out and reintroduce them into the population,” says Aryn Wilder

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at the San Diego Zoo Wildlife Alliance.

Their model revealed that, after 10 generations, the northern white rhinos in these simulations were not inbred – instead, they were a healthy, genetically diverse bunch. That is good news for the subspecies’ future because inbred animals tend to be more susceptible to disease and less likely to survive.

Wilder then compared the genes of those simulated rhinos to genes from the southern white rhino, which bounced back from a population of around 100 individuals in the early 1900s to about 20,000 today. “Compared to the southern white rhino, there’s actually more genetic diversity in the northern white rhino genome,” she says.

But discovering that northern white rhinos are not genetically doomed is only part of the challenge. Researchers would still need to chemically coax these frozen skin cell lines into viable sperm and egg stem cells. There is also no guarantee that southern white rhino surrogates can successfully carry the embryos of the northern white rhinos. Another way forward is cloning: the banked cell lines could be used to create a genetic copy of the deceased animals.

“There is so much more to conserving rhinos than genetic diversity in cell lines,” says Terri Roth at the Cincinnati Zoo and Botanical Garden in Ohio. “But good news on any front is still worth celebrating in these tough times.”

Evolutionary Applications, in press

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