The entire world population of the northern white rhinoceros can be counted on a single hand. On the brink of extinct, the three remaining members of this rhino subspecies are kept under watch 24/7 by armed guards. To count the total number of fertile rhinos out of these three, you would not even need a hand. Sudan, the last male northern white rhino on Earth, is effectively sterile due to low sperm count. The females, Najin and Fatu, suffer from orthopedic and uterine disorders, respectively, that also rule out pregnancy. By traditional standards, the northern white rhinoceros is as good as gone.
However, stem cell technology appears to be a promising avenue to save the northern white rhino. Stem cells are immature precursor cells that can develop into a variety of mature cells and treat otherwise fatal illnesses. In this case, rather than to heal a damaged organ, stem cells will revive the entire northern white rhino population. A team of conservation biologists, led by senior researchers Oliver A. Ryder of the San Diego Zoo Institute for Conservation Research and Thomas B. Hildebrandt of the Leibniz Institute for Zoo and Wildlife Research, have written a protocol that uses stem cells to save the northern white rhino (Saragusty et al., The Leibniz Institute, Zoo Biology).
Although stem cells are usually found in embryos, the researchers plan to use iPSCs (induced pluripotent stem cells). These cells are created when mature cells, such as skin cells, are reverted to their stem cell stage in the laboratory. This is advantageous because the rhinos are incapable of breeding naturally to produce an embryo. The scientists plan to use iPSCs to generate egg and sperm, which will be combined into embryos and implanted into surrogates. According to Ryder, “genetic resources … with the capability to establish induced pluripotent stem cells are the basis for hope that a viable population of northern white rhinoceros can be produced” (Ryder, 2016).
Skin samples provide the additional benefit of maximizing genetic diversity. The living three northern white rhino are all related as parent-offspring. Sudan is the father of Najin, who is the mother of Fatu. Using iPSCs, researchers can apply skin cell lines that have been previously extracted from unrelated, now-deceased rhino. Institutions such as the Leibniz Institute for Zoo and Wildlife Research and the San Diego Zoo Global have stored skin samples from a total of 12 individuals.
Opponents of this endeavor may believe that this relatively new and expensive procedure is unjustified for a dying subspecies. Out of the countless species that go extinct every year, it is unclear if the northern white rhino is particularly valuable ecologically. Furthermore, the northern white rhino has a related subspecies, the southern white rhino, which has not yet descended to endangered status.
However, people have an ethical obligation to take this opportunity because the northern white rhino was driven to near-extinction by human activity. Once abundant in Africa, the northern white rhino was decimated by poaching. Although conservationists made efforts to preserve the remaining population in captivity, failed breeding efforts caused the meager remaining population to continually decrease.
This effort also has implications beyond a single subspecies. iPSCs serve as a potentially revolutionary tool for conservation, not just for the northern white rhino but also for other critically endangered mammals. iPSCs offer a more advanced and flexible alternative to conception from naturally extracted eggs and sperm. Since we are currently in the sixth mass extinction event in Earth’s history, connecting modern experimental technology to conservation has been increasingly crucial. By pioneering the use of the technology in conservation, researchers can pave the way for future applications.
Stem cell technology gives hope that near-extinct species may one day roam their natural habitats in sustainable populations. If they are allowed the resources, these researchers can both rescue the northern white rhino and optimize their protocol for the rescue of other species.
Saragusty, J., Diecke, S., Drukker, M., Durrant, B., Friedrich Ben-Nun, I., Galli, C., Göritz, F., Hayashi, K., Hermes, R., Holtze, S., Johnson, S., Lazzari, G., Loi, P., Loring, J. F., Okita, K., Renfree, M. B., Seet, S., Voracek, T., Stejskal, J., Ryder, O. A. and Hildebrandt, T. B. (2016), Rewinding the process of mammalian extinction. Zoo Biology, 35: 280–292. http://dx.doi.org/10.1002/zoo.21284
“Seeking to rewind mammalian extinction.” Eurekalert. The American Association for the Advancement of Science, 2016, http://www.eurekalert.org/pub_releases/2016-05/zsos-st042916.php. Accessed 6 September 2016.