How “The Single Known Hybrid Between Northern And Southern White Rhinoceroses” Could Save A Species On The Brink

In 1977, a rhino was born at Dvůr Králové Zoo. She was named Nasi, and came as a bit of a surprised because her mother, a northern white rhino called Nasima, had only had contact with one male rhino. Why was that so strange? Well, he was an entirely different species.

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Hybrids like Nasi crop up from time to time, but as the only known hybrid between a northern and southern white rhino, she really stood out – not least because northern white rhinos are presently on the brink of extinction with just two individuals left. But a solution inspired by Nasi’s very existence hopes to change that.

A world-first attempt at in-vitro fertilization taking a lab-created rhino embryo and transferring it into a surrogate saw success in 2023. Oocytes collected from Elenor, a southern white rhino who lives at the Pairi Daiza Zoo in Belgium, were transferred to a surrogate southern white rhino in Kenya called Curra.

Jan Stejskal, coordinator of the BioRescue project, was one of the people who had gone to check on the status of her pregnancy when they received a worrying call: Curra was sick, and it was happening fast. She died as a result of exposure to bacteria resurrected by heavy rains, but a necropsy revealed the IVF had been a success as the team found a 70-day-old rhino fetus.

 

It was a tragic moment, but one that came with a thin silver lining of hope as it demonstrated the procedure was possible. Now, the goal is to complete the same IVF process, this time using oocytes from Fatu – one of the last two remaining northern white rhinos. She and her mother, Najin, are both female, but Fatu is the only one healthy enough to undergo the procedure needed to retrieve oocytes.

Will the process be harder now that the embryo is being transferred from one rhino species to another? It’s a good question, but one that takes us back to Nasi.

This shows us that hopefully southern white rhino should be ideal surrogate mother for northern white rhino, but until we have a baby on the ground, we cannot say this for 100 percent certain.

Jan Stejskal

“We do not know whether there might be some barrier,” said Stejskal to IFLScience. “On the other hand, what we do know is that there was a crossbred born between southern white rhino and a northern white rhino.”

“It was actually born in our zoo, but it was a coincidence because a female northern white rhino came from another zoo, and no one noticed that she was pregnant. Two or three months after her arrival, she gave birth to a baby. In the previous zoo, she was only with a southern white rhino male. It was clear that it had to be him [who was the father]. This shows us that hopefully southern white rhino should be ideal surrogate mother for northern white rhino, but until we have a baby on the ground, we cannot say this for 100 percent certain.”

That Nasi was born gives us some degree of confidence that a southern white rhino could carry a northern white rhino to full term. However, the situation continues to be a tricky one when we consider the health of that animal, as well as the population as a whole.

When you experience such a huge reduction in your population like the northern white rhino has experienced, you lose a lot of genetic diversity [...] We're creating gene editing targets so that we can begin to edit northern white rhino cell lines to help bring back those lost genetics.

Matt James

“The single known hybrid between northern and southern white rhinoceroses was Nasi, born 1977 and died in 2007,” wrote the authors of a 2018 study into the recovery potential of northern white rhinos. “This individual reached adulthood but never reproduced and was in relatively poor health. Nothing in our findings would invalidate the interbreeding of NWR [northern white rhinos] and SWR [southern white rhinos]; however, given the death of the one remaining male NWR and the limited number of NWR cryopreserved gametes, the amount of NWR genetic variation that could be maintained through interbreeding is likely limited.”

“While some might argue against efforts to genetically rescue the NWR subspecies given the close evolutionary relationship with the SWR, this makes using the SWR as a surrogate more likely to succeed, and the benefits and lessons of any genetic rescue effort could apply to other rhinoceros species, as well as to mammalian species with similar life history and conservation concerns.”

The genetic viability of the offspring going forward is something that BioRescue have already been focusing on as they’ll need to find a way to increase it if they’re going to establish a stable population. Here, Colossal Biosciences have been lending a helping hand to figure out which are the best and most crucial genes to try and restore.

“When you experience such a huge reduction in your population like the northern white rhino has experienced, you lose a lot of genetic diversity,” Colossal’s Chief Animal Officer Matt James told IFLScience. “So, Colossal has teamed up with BioRescue to develop a technological pathway that'll allow us to explore historic northern white rhino population genetics so we can understand what the population was like before we lost 99 percent of it.”

“We can compare that to what exists in the two remaining northern white rhinos and the cell lines that have been banked, and then we can identify alleles that were lost over time. That could include genes that are responsible for very specific traits that might improve things like adaptability and disease resistance.”

“Then we're creating gene editing targets so that we can begin to edit northern white rhino cell lines to help bring back those lost genetics. That means as BioRescue has success in restoring the northern white rhino and growing its population, Colossal can help address the genetic diversity of that growing population and ensure it's as diverse and healthy as possible.”

From one unique hybrid to a multi-faceted approach to saving one of central Africa’s most iconic creatures, it’s already a remarkable story. Fingers crossed we hear the pitter patter of baby northern white rhino hooves soon.