Things look pretty bleak for the northern white rhinoceros. Since the death of Sudan, the last male, the entirety of the subspecies has dwindled to only two females. But a group of scientists is churning away on a high-tech save involving carefully cryopreserved cells and tissue cultures from long-dead northern white rhinos. And a new study on the genetics of these precious samples suggests that they are diverse enough to successfully seed a recovered population in the future.
Scientists at the San Diego Zoo are using their conservation genetics facility, along with cryopreserved genetic and cell samples, to develop new techniques that could be the Hail Mary play that brings back the northern white rhino. The plan involves taking stored, northern white rhino genetic material from the San Diego Zoo Institute for Conservation Research’s Frozen Zoo, and having southern white rhino females—a closely related subspecies—act as surrogate moms for the developing offspring.
This can be done in multiple ways, including by turning northern white rhino cell lines into stem cells and then into eggs and sperm, or by cloning (placing northern cell line DNA into a southern rhino egg cell). But before investing time, money, and resources in any approach, the researchers needed to know what they were working with.
“We wanted to know if the genetic material we have in the Frozen Zoo is actually viable in terms of having enough genetic diversity,” Cynthia Steiner, the conservation geneticist at the San Diego Zoo who directed the study, told Earther.
Genetic diversity—or rather a lack of it—is the bane of tiny populations. Without enough diversity, “inbreeding depression” can arise, causing increased risk of disease and extinction (similar to what has been plaguing cheetahs). If the northern white rhino cell lines were too similar to one another, then any recovery population might have a difficult time persisting over the long term.
So, Steiner and her colleagues investigated the genetic history and diversity of cells from nine cryopreserved northern white rhino individuals, and compared them to four southern white rhinos. The team sequenced all thirteen genomes, looking for differences and analyzing them to get an idea of the history of both populations from a genetic perspective.
Their results, published today in the journal Genomics Research, are very promising for the future of the northern white rhino. The genetic diversity among the nine northern individuals was surprisingly high, nearly equivalent to that of the southern rhinos—which came from a much bigger wild pool. This is interesting, because the two subspecies have had dramatically different fates over the last century.
Southern rhinos went into a severe population decline about a century ago, and then climbed back, says Steiner. But the northern population was doing well until a few decades ago.
“So, we didn’t know what to expect in terms of genetic diversity when comparing the two populations,” said Steiner.
The results suggest that from a genetic standpoint at least, a recovery scenario is still very possible.
“We know the southern white rhino was able to recover from very few individuals—between 20 and 50 individuals a century ago—to the numbers we have now, which is about 20,000,” Steiner said. “A similar recovery could be possible if we succeed with a genetic rescue of the northern white rhino.”
Steiner says the plan is now to push forward, honing their findings by adding genomes of more cryopreserved individuals. Some future genetics work will address just how much interbreeding has historically occurred between the northern and southern rhinos.
Whatever secrets the team unlocks, thankfully for now, the future of the northern white rhino just received another green light.