In Jurassic Park, a little 200-million-year-old blood was all it took to revive rampaging hordes of dinosaurs. In the real world, we鈥檙e struggling to save to species that are still living. Biologists are now resorting to desperate measures to bring the northern white rhino back from the brink.
The northern white rhino is one of two subspecies of white rhinos. Around 20,000 southern white rhinos still survive in southern Africa, but their northern cousins in central Africa appear doomed. Those living in the wild have been wiped out by hunters and poachers, and those living in captivity did not breed well enough to survive.
鈥淭he northern white rhino did not fail in evolution, it failed because it was not bullet-proof,鈥� says Thomas Hildebrandt of the Leibniz Institute for Zoo and Wildlife Research in Germany, part of an international team trying to save the northern white rhino.
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Two remain
The last surviving male, called Sudan, died earlier this year. Only two females remain 鈥� Sudan鈥檚 daughter Najin and granddaughter Fatu, who are under heavy guard in Kenya 鈥� and they have serious reproductive problems.
In theory, it should be possible to recreate a thriving population from frozen tissue samples and sperm that were gathered from northern white rhinos. We also have living cell lines derived from 12 of the last northern white rhinos to die.
Late last year, the team fertilised southern white eggs with some of the frozen sperm from northern whites, creating hybrid embryos that developed to the stage where they are ready to implant. They plan to implant these hybrid embryos into southern white females in the next few months.
The team want to establish a small population of such hybrids, but they see it very much as a backup 鈥� a way of preserving some of the northern subspecies鈥� genes. They hope to achieve a live birth of a pure northern rhino within three years if they get permission from Kenyan authorities to extract eggs from Najin and Fatu.
If that doesn鈥檛 work, the plan is to derive embryonic stem cells (ESCs) from the living cell lines, and use those to generate eggs and sperm. This has only been achieved in mice so far but the team is confident they will achieve this in rhinos within ten years 鈥� ideally using hybrids as the surrogate mothers. They have already derived ESCs from the embryos of southern white rhinos.
Finally, if all this fails, the team will try to breed something like the northern white rhino from the hybrids, assuming the team manages to create them. But this is no easy task.
In a first generation hybrid, each cell will have one set of chromosomes from the northern white father and one from the southern white mother. But these chromosomes will swap DNA when sperm and eggs form, mingling the genomes of the two subspecies together in a way that is impossible to completely reverse with conventional breeding.
Do we even need to save a mere subspecies? Absolutely, argue the researchers. They say there substantial differences between the two white rhinos, from the hairy ears of the northern white to the larger size of the southern. Rhinos also play a big part in shaping landscapes, they say, so it鈥檚 important to reintroduce them to central Africa.
We have to pursue all avenues, says Jan Stejskal of Dvur Kralove Zoo in the Czech Republic, where some of the last northern whites were kept. 鈥淲e have to work on field conservation, on demand reduction [for rhino horns] and on the newest science.鈥�
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Nature Communications
