The nearly extinct northern white rhino may not be completely lost.
For the first time, rhinoceros embryos have been made in the lab. Scientists injected preserved sperm from a male northern white rhino into eggs of female southern white rhino, a closely related subspecies. The embryos were incubated until the cells begin to differentiate, a stage at which they can be implanted into a surrogate mother, researchers report July 4 in Nature Communications.
The new feat is “one of the really crucial steps” to eventually producing new rhino calves, says study coauthor Jan Stejskal, coordinator of northern white rhino conservation efforts at the Safari Park Dvůr Králové in the Czech Republic. Eventually, researchers hope to implant similar embryos into female southern white rhinos or hybrid northern-southern white rhinos.
If it works, it could provide hope for bringing back a species on the brink of extinction. Sudan, the last male northern white rhino, died in March. Only two females remain in Kenya, both in captivity and unable to reproduce naturally. In comparison, there are more than 20,000 southern white rhinos left.
In the new study, the scientists used eggs from female southern white rhinos and sperm preserved from three male northern white rhinos. While the new embryos are a hybridized northern-southern white rhino mix, the ability to create them is “a saving mechanism for the genes of the northern white rhinos,” says study coauthor Thomas Hildebrandt, a reproduction biologist at the Leibniz Institute for Zoo and Wildlife Research in Berlin.
Hybrid rhinos, if they are ever born, could serve two purposes. They may be more compatible surrogate mothers for an eventual pure northern white rhino embryo since they will share more DNA with the babies. And theoretically, the hybrids could be selectively bred for the northern rhino genes, eventually creating a pure northern white rhino — a process that would take many generations and span multiple decades.
In a potentially quicker way to birth a pure northern white rhino, researchers plan to harvest eggs from the two remaining females and combine them with preserved northern white rhino sperm. If successful, a northern white rhino calf could be born within the next three years, Hildebrandt says.
Stem cell technology may play an important role in saving the rhinos, too. The team was able to derive pluripotent stem cells, which can turn into any cell in the body including eggs and sperm, from two pure southern white embryos. Hildebrandt says that there are 12 frozen cell lines from northern white rhinos, six of which are genetically distinct – important for avoiding inbreeding. If researchers can turn these skin cells first into pluripotent stem cells and then eggs and sperm, it would be another way to create a pure northern white rhino embryo.
For now, other scientists caution against too much optimism. “Saving a species or a subspecies takes a lot more than the science,” says Terri Roth, an animal reproductive physiologist at the Cincinnati Zoo and Botanical Garden. Africa is in the midst of a rhino-poaching epidemic, she says. In 2013, poachers killed 13 rhinos; in 2017, over 1,000 were killed. Any efforts to reestablish the northern white rhino population will need to address this crisis, she says (SN Online: 12/16/13).
Hildebrandt agrees. The northern white rhino didn’t go extinct because it failed at evolution, he says, “it failed because it is not bulletproof.”