Africa

Only two of these rhinos are left; should scientists intervene?

In a photo from San Diego Zoo Global, Sudan, the last male northern white rhino, who died March 20 at the Ol Pejeta Conservancy in Kenya. Source: SAN DIEGO ZOO GLOBAL

Even if the technology can bring back the northern white rhinoceros, there is debate over whether it should be used.

When the last male northern white rhinoceros died in March, people mourned the beloved mammal’s step toward extinction.

With no members of the subspecies left in the wild and just two females remaining in captivity, it felt as if the last bit of sand was draining through the rhino’s hourglass.

But several teams of scientists are working to flip the hourglass back over.

One group, led by researchers at the San Diego Zoo Institute for Conservation Research, hopes to revive the northern white rhino using preserved cells. In a study published Thursday in Genome Research, the scientists sequenced the DNA of these cells and concluded that they hold a promising amount of genetic diversity for re-establishing a viable population of northern whites.

With the right advances in assisted reproduction or cloning, there could be a second chance for this “unique form of rhinoceros,” said Oliver Ryder, director of conservation genetics at San Diego Zoo Global.

Not everyone agrees that having the capacity to bring back the northern white rhino means it should be done. Critics question whether the buzz around resurrecting a functionally extinct creature takes attention and resources away from other animals with greater chances of survival.

They also point out that any resurrected northern white rhinos would likely remain in captivity, rather than roaming free in their former habitat in central and eastern Africa, where poaching for horns remains a serious threat.

In their study, Ryder and his colleagues focused on the feasibility of recovering the northern white rhino using cells stored in the Frozen Zoo, a large collection of cryopreserved samples at the San Diego Zoo. These cell lines represent eight presumably unrelated northern whites, Ryder said.

The researchers sequenced these genomes and compared them to genomes from southern white rhinos, the northern white rhino’s closest kin, which underwent a spectacular recovery under protection over the past century, although it remains near-threatened.

They confirmed scientists’ long-held hypothesis that the two rhinos are subspecies, rather than distinct species. This close relationship might bode well for someday using southern white rhinos as surrogates for northern white embryos.

The scientists also discovered sufficient genetic diversity in their northern white rhino samples when compared with the southern white rhinos, Ryder said. “If it came down to the materials in the Frozen Zoo, we could turn those cells into animals.”

But Marty Kardos, an evolutionary biology researcher at the University of Montana, cautioned that the southern white rhino comparison is “not necessarily worth banking on.” Purely by chance, harmful mutations could exist at high frequency among the northern white rhinos and have a detrimental effect, he said.

Dr. Oliver Ryder, of the San Diego Zoo Global's Frozen Zoo, inspecting cell cultures from a store of tissue and genetic material.
In a photo from San Diego Zoo Global, Dr. Oliver Ryder, of the San Diego Zoo Global's Frozen Zoo, inspecting cell cultures from a store of tissue.

Jason Gilchrist, an ecologist at Edinburgh Napier University in Scotland, questioned the point of reviving an animal that can’t return to its native way of life. “As an ecologist, what I want is to see wild ecosystems functioning as close to naturally as they can,” he said.

Joseph Bennett, a conservation researcher at Carleton University in Ontario, feels the northern white rhino is a good candidate for resurrection because there’s a relatively high chance of success compared to more ambitious projects like the de-extinction of the woolly mammoth or passenger pigeon.

It could be a “really nice ‘good news story’ for people,” he said.

Cathy Dean, chief executive of the charity Save the Rhino, said that efforts to revive the northern white rhino likely attract different sources of funding than conserving remaining wild rhinos. Still, she wishes other rhinos, like the critically endangered Sumatran, Javan and black rhinos, received nearly as much airtime as the northern white, she said.

Ryder said his team’s efforts are not in lieu of, but in addition to, efforts to conserve wild animals, adding that “we are seeing species go extinct in spite of a global commitment” to protect them.

In light of that, he said, providing “more options for the existence of species into the future is an appropriate quest.”

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