SUDAN, the last male northern white rhinoceros on Earth, died in March 2018. He is survived by two females, Najin and her daughter Fatu, who live in a conservancy in Kenya. This pair 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 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.
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;… and subsenquently 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.
Excerpts from Animal Conservation: Drinking in the last-chance saloon, Economist, July 7, 2018, at 66.