What do you picture when asked to imagine life for an animal in the African savannah? Do you imagine a magnificent landscape crowded with watering holes surrounded by wildlife? One century ago, over half a million rhinos grazed the African grasslands. So, how could the northern white rhinoceros now rely on a Petri dish to survive?
Above: One of two remaining northern white rhinos pictured roaming in the Ol Pejeta Conservancy in Kenya. Image courtesy of Karimi Ngore.
The answer is simple: ivory. Since the colonial era, the practice of poaching rhinos for jewelry and medicine has played a major role in the endangerment of this species. Today, just two elderly females, Najin and Fatu, remain under the protection of armed guards. Scientists have classified the subspecies as functionally extinct.
Is the survival of this once-populous species a lost cause? How could the northern white rhino regain its numbers without a single living male or any female capable of gestation? Dr. Thomas Hildebrant of the BioRescue consortium has uncovered a method that might help save northern white rhinos and change the future of biodiversity.
To preserve the species, Hildebrant and his team have turned to in-vitro fertilization (IVF). By utilizing both males and females of a similar subspecies—the southern white rhino—Hildebrant believes that BioRescue has “achieved together something which was not believed to be possible.”
Above: Researchers analyzing pluripotent stem cells from northern white rhinos. Image courtesy of the Biorescue consortium.
While humans use IVF to counter infertility issues or avoid passing on genetic mutations to their children, the BioRescue team explored another application for this technology. To create embryos scientists first collected oocytes of female southern white rhinos with a technique known as ovum pick-up (OPU). Hildebrant developed new instruments for rhino OPU including a transrectal tool and a double-lumen needle, which can reach ovaries and aspirated follicles to release immature eggs. Once gathered, they incubated the oocytes and repeated the process on the remaining female northern white rhinos. In light of the small number of rhinos to obtain oocytes from, researchers from the San Diego Zoo are working to transform preserved skin cells from northern white rhinos into iPS cells, which they can use to create new oocytes vital to the genetic future of the species.
This is only half of the story. The creation of an embryo through IVF also requires intracytoplasmic sperm injection (ICSI), for which BioRescue scientists have developed a tedious but effective protocol. A major limitation for the team was the death of Sudan, the last male northern white rhino, in 2018. Moreover, only three bulls of the northern species had preserved semen samples, limiting the potential gene pool even further. Scientists assessed the quality of these samples by measuring their ability to sustain pronuclei formation and initiate cleavage in oocytes. At first, poor motility limited the fertilization rate of these samples to 30%. However, scientists realized that these sperm needed an energy boost: an electrical activation protocol just after sperm injection raised the fertilization rate from 30% to a remarkable 90%.
After completing OPU and selecting sperm from northern and southern white rhinos, the lifelines were transported to the Leibniz Institute of Zoo and Wildlife Research. Just 38.6% of oocytes developed a polar body, indicating suitability for ICSI. BioRescue researchers injected 19 oocytes with southern white rhino sperm and 13 with northern white rhino sperm, resulting in seven total blastocysts with almost all containing detectable inner cell mass. Additionally, BioRescue used fibroblast growth factor (BFGF) and serum replacement—two protocols typically used to culture human embryonic stem cells. This technique has vastly improved the likelihood of embryo development and the future of the northern white rhino.
Has global scientific initiative secured the future of the most critically endangered animal? Unfortunately, not yet. According to National Geographic Explorer Ami Vitale, these rhinos “look prehistoric, and they had survived for millions of years, but they couldn’t survive us.” Conservationists like Vitale point out that groundbreaking research in reproductive assistance is just one step in preserving species like the northern white rhino. To ensure a safe future for the thousands of species currently categorized as critically endangered, we must not only turn to scientists for novel methods but also critically examine our own role in the preservation of life and biodiversity.
Written by Stella Tekotte, this article was selected as a winner of our 2024 High School Science Communication Challenge. From Raleigh, N.C., Tekotte is a sophomore at Wakefield High School. In her free time, she enjoys playing soccer, hiking with her family, advocating for UNICEF, and reading a great book.