By Sophie Teall
A new milestone has been accomplished in the mission to save the northern white rhino (Ceratotherium simum cottoni). There are only two known northern white rhinos left, both of whom are females. Without the ability to reproduce, this subspecies is functionally extinct. An international team are now one step closer to using assisted reproduction technology (ART) including in vitro fertilisation (IVF) to increase subspecies numbers and bring them back from the edge of extinction.
The northern white rhino is one of the two subspecies of white rhinoceros. Native to Africa, the northern white rhino would have historically roamed through regions of Uganda, South Sudan, the Central African Republic and the Democratic Republic of the Congo. Now only two remain. Poaching and land loss pose a large threat to all five rhino species, and the northern white rhino is one of the four species considered endangered due to these actions. Mother and daughter, Najin and Fatu spend their days grazing in Ol Pejeta Conservancy in Kenya, where they are under the constant watch of armed security. While they have both had their horns sawn off to reduce motive for poaching, these two individuals are too valuable to risk losing.
The subspecies’ southern counterpart, the southern white rhino, is the only rhino species not considered endangered. This is not without intense conservation effort. At the beginning of the 20th century, less than 100 rhinos remained; optimistically, as of 2015, there were estimated to be 19,000. While the subspecies is still classified as Near Threatened, this offers hope for the northern white rhino. However, the lack of living male northern white rhinos makes their extinction more challenging to combat. Additionally, neither Najin and Fatu can carry a pregnancy to full-term due to issues with their reproductive tract, introducing an additional level of complexity.
An international team are working to meet this challenge. The BioRescue team includes members from Leibniz Institute for Zoo and Wildlife Research, Safari Park Dvůr Králové, Kenya Wildlife Service, Ol Pejeta Conservancy and Aventea laboratory. The team hopes to use ART to create northern white rhino embryos which can then be carried to full-term by a southern white rhino surrogate. This would allow new members of the subspecies to be born with the hope of eventually forming a new population of northern white rhinos.
The first part of the mission has already been successful. Before the deaths of the last two male northern white rhinos, Sudan and Suni, sperm cells were collected and stored. In 2019 and 2020, egg cells were collected from Najin and Fatu. These two cells can be carefully combined through IVF to produce embryos, which can then be stored in liquid nitrogen until they are ready to be implanted into the surrogate mother. By 2019, three embryos were successfully produced. In January 2021, despite challenges and delays due to the COVID-19 pandemic, the team announced that two more had been made. This brought the total up to five. All five of these embryos are offspring of the younger rhino Fatu, and it’s thought that her mother’s eggs were less viable due to age and the presence of a tumour in her abdomen.
Now the next step can begin. Four female southern white rhinos have already been selected as potential surrogate mothers and are kept at Ol Pejeta. Additionally, a sterilised southern white rhino bull was transferred from Lewa Wildlife Conservancy in November 2020. He has already fathered several offspring in the breeding programme at Lewa, so was selected to be removed from that programme and play a vital role in northern white rhino conservation. Due to the limited number of embryos, it is vital to optimise their use and know when a potential surrogate mother is fertile. Once his sterilisation has been confirmed in March 2021, his behaviour will be observed and used to indicate when a potential surrogate is capable of receiving an embryo. The BioRescue team hopes that they will be able to deliver their first calf in 3 years.
This progress is certainly an exciting move in the right direction, however, there’s still a significant amount of work to be done. Rhino reproduction is low, with the mother only being able to carry a single calf at a time. The gestation period lasts between 14 and 18 months, and the mother stays with her calf for two to three years before she is ready to mate again (Hirst et al.1975). While it is hoped that this work will lead to the development of a wider population of rhinos within the next two decades, the prospect of having a viable population, consisting of over 20 unrelated individuals, is still a long way off. There’s an additional time constraint; any newborns would ideally be able to learn subspecies-specific social knowledge from Najin and Fatu. Najin and Fatu are 31 and 20 years old respectively. Both Suni and Sudan died in their mid-30s, so to achieve this goal it is critical that northern white rhino offspring are born soon.
The complexity of this work serves as an urgent reminder. While technological advances will hopefully make it possible for the northern white rhino to be rescued back from the brink of extinction, populations cannot be allowed to drop until ART becomes the only option. Once a species is extinct, it is gone forever. The case of the southern white rhino offers reason for optimism and shows that it is possible to drastically change the trajectory of a population before they get to this point. Hopefully, the northern white rhino will one day join them as a conservation success story.
Biorescue.org. 2021. Happy end to a challenging year: Two new northern white rhino embryos created at Christmas – now there are five | Biorescue. [online] Available at: <http://www.biorescue.org/en/news/happy-end-challenging-year-two-new-northern-white-rhino-embryos-created-christmas-now-there> [Accessed 5 February 2021].
Hirst, S., Geist, V. and Walther, F., 1975. The Behaviour of Ungulates and Its Relation to Management. The Journal of Wildlife Management, 39(2), p.454.
Save The Rhino. 2021. Rhino populations | Rhino Facts | Save the Rhino International. [online] Available at: <https://www.savetherhino.org/rhino-info/population-figures/> [Accessed 5 February 2021].