When a northern white rhino died at the San Diego Zoo last November, that left three of the animals in the world, all living in a wildlife preserve in Kenya. After decades of poaching and civil wars, the rest of the population has disappeared. The three who remain are unable to breed. But an international coalition of researchers is hoping to save them from extinction in the lab.
First, the scientists plan to harvest eggs from the two remaining females—a delicate procedure that they're practicing first on infertile southern white rhinos, who still have a population in the thousands. When I first called Thomas Hildebrandt, who is helping lead the effort from the Leibniz Institute for Zoo and Wildlife Research in Berlin, he couldn't come to the phone because he was at a zoo, midway through a rhino egg collection.
"It seems that this technique has no impact on the health of the animals, it can be performed every two to six months, and it allows us to harvest oocytes [eggs] for in-vitro procedures from these individuals," Hildebrandt says. "[This can] show the proof of principle—that you can produce embryos in the test tube and then transfer them and produce offspring of them."
After collecting northern white rhino eggs, the researchers will attempt in-vitro fertilization with frozen rhino sperm. Because the remaining rhinos can't carry a pregnancy, a related southern white rhino might serve as a surrogate. All of this is speculation—no one has ever used in-vitro fertilization in rhinos before, or tried to use a surrogate rhino.
There's another big challenge: the three remaining rhinos are all related (the females are mother and daughter, and the 42-year-old male rhino is both father and grandfather). The handful of frozen sperm samples available, from the San Diego Zoo's Frozen Zoo, can't provide enough genetic diversity to create a healthy population of new rhinos. So the researchers also plan to use some genetic engineering.
Using a technique that won a Nobel Prize in 2012, it's possible to turn any cell, including skin cells from the frozen zoo, into stem cells called iPS, or induced pluripotent stem cells. Those cells can then be programmed to become sperm or eggs—and then mixed into the in-vitro fertilization process to add genetic diversity.
In another technique, a southern white rhino embryo might be sterilized, and then stem cells from the northern white rhino could be added. "That establishes the germ line," Hildebrandt says. "Then these chimeras will produce pure northern white rhino gametes."
Hildebrandt's lab has spent the last two years working on a shoestring budget. "It's really disappointing, because we're fighting against time," he says. "There's not the time right now to wait for a better funding situation, because this male and two remaining females, they're aging fast, and nothing was done over the last six years."
Others argue that the money that will need to be invested in the process could be better spent protecting the southern white rhino—which still has a fairly large wild population—from poachers. But Hildebrandt believes that habitat protection and the experimental anti-extinction techniques should go hand in hand.
"The northern white rhino is technically extinct, without the application of the procedure we've developed right now," Hildebrandt says. "They are infertile, they can't produce anymore, and they will be dead maybe in 20 years. The male may die in less than a year, and then there are only two females left."
He's optimistic that the science could work quickly enough to produce a baby rhino before the last existing northern white rhino dies. Then—because the southern white rhino population demonstrated in the past that rhinos can bounce back—he hopes that northern white rhinos could eventually be reintroduced into the wild.
"One hundred years ago, the southern white rhino population was down to 50," he says. "Now we are up to 20,000 ... I think that was a very great success story, and we could achieve the same with the northern white rhino. Maybe not 20,000, but 1,000."
The same techniques could also potentially be used for other animals on the verge of extinction, or even after they've gone extinct. Hildebrandt plans to work on the Sumatran rhino next. "There are only three in captivity in Sumatra, and there may be three to four still left in the wild in Borneo," he says. "It's a similar situation—we can apply the same technology we develop for the northern white rhino in the same manner in Sumatran rhinos."