SUDAN, the last male northern white rhinoceros on Earth, died in March. He is survived by two females, Najin and her daughter Fatu, who live in a conservancy in Kenya. This pair (pictured) are thus the only remaining members of the world’s most endangered subspecies of mammal. But all might not yet be lost. Thomas Hildebrandt of the Leibniz Institute for Zoo and Wildlife Research, in Berlin, in collaboration with Avantea, a biotechnology company in Cremona, Italy, is proposing heroic measures to keep the subspecies alive. In a paper just published in Nature, he and his colleagues say that they have created, by in vitro fertilisation (IVF), apparently viable hybrid embryos of northern white rhinos and their cousins from the south. This, they hope, will pave the way for the creation of pure northern-white embryos.
IVF seems the last hope for the northern white rhino. Though stored sperm from Sudan and several other males are available, both Najin and Fatu now seem unable to conceive. This means, if the subspecies is to be preserved, that one or both of them will have to have some eggs removed from their ovaries and combined with stored sperm in a Petri dish.
Extracting rhinoceros eggs is hard. The animals’ ovaries are over a metre deep inside them, meaning that the extraction procedure, which employs a probe with a sharp needle attached to it to suck the eggs out, is hazardous. But practice makes perfect, so the team started by obtaining instead some eggs from a southern white rhino, the northern’s close cousin. They combined these with some of their cache of northern sperm and coaxed seven of the resulting zygotes through the early stages of embryonic development, to the point where they could be implanted in the uterus of a southern white, who would act as a surrogate mother, with a reasonable hope of success.
That has not yet happened. The seven embryos are now in a freezer awaiting the results of research on how best to transfer them to surrogates. In the meantime, having proved their technique with these hybrids, Dr Hildebrandt and his colleagues now hope to create more embryos, this time using eggs from the two remaining female northern whites.
Even if they succeed, though, it will be a long haul back for the northern white rhino. Members of any new generation resulting from IVF will have then to be bred with each other to create subsequent generations—with all the risks of reduced biological fitness which such incest entails. It is not so much a gene pool that Dr Hildebrandt is working with as a gene puddle.
Then there is the question of what to do with the resulting animals. Analysis of other rhinoceros species, both in Africa and Asia, points to a viable population in the wild needing to be at least 500 strong. Even if such a group could be created, and not collapse from lack of genetic diversity, releasing it into the tender mercies of what remains of Kenya’s savannah would be risky. The reason the northern white has come so close to extinction—poaching—is unlikely to go away anytime soon.
Dr Hildebrandt’s work is thus a half step along what is likely to be a very long road indeed. Charismatic megafauna rhinoceroses may be. But whether that charisma can sustain enough effort for long enough to save the northern white is about to be tested.