The female Fatu is one of only two surviving specimens of the northern white rhinoceros. (Image: BioRescue / Rio the Photographer)
Today only two females live from the northern white rhinoceros. But scientists have already created nine rhinoceros embryos using artificial insemination, which can now be used by surrogate mothers. In preparation for the transfer, a rhinoceros bull was sterilized to indicate that the surrogate mothers were ready to receive. If it signals that the females are ready to reproduce, the embryo transfer can take place.
Only two specimens of the northern white rhinoceros (Ceratotherium simum cottoni) exist worldwide today: the two females Najin and Fatu. From the last two bulls of the pachyderms, however, sperm samples were frozen before their death, with which one could artificially fertilize egg cells taken from the females. Since Najin and Fatu both cannot conceive due to health problems, these embryos would then have to be carried by surrogate mothers. In 2019, scientists succeeded for the first time in extracting ten immature egg cells from the female rhinoceros. Further collections followed later, which the researchers were even able to fertilize with the sperm of the deceased males in the laboratory, thus generating five embryos.
More embryos
A research team led by Thomas Hildebrandt from the Leibniz Institute for Zoo and Wildlife Research (IZW) has now tried to create even more viable embryos. To do this, they put Fatu, the younger female rhinoceros, under general anesthesia and removed 19 egg cells from her ovaries with an ultrasound-guided probe. The immature eggs were then incubated in the laboratory for maturation. The scientists then fertilized 14 of these egg cells with thawed sperm from the deceased white rhinoceros bull Suni. To do this, they used a special in vitro method, the so-called intracytoplasmic sperm injection (ICSI method). One sperm is injected directly into the cytoplasm of an egg cell.
In fact, four fertilized egg cells developed into viable embryos, which are now stored in liquid nitrogen. “We are thrilled with the results of the last egg retrieval in March,” said Najib Balala from the Kenya Ministry of Tourism and Wildlife. The egg cells of the now nine embryos of the northern white rhinoceros all come from Fatu. It is uncertain whether the 31-year-old Najin’s egg cells can be removed and fertilized again in the future: During the most recent operation, Hildebrandt and his colleagues only performed a light anesthesia and ultrasound examination on her. Based on the results of the ultrasound, the team decided not to attempt egg retrieval because Najin had not developed enough promising eggs.
Sterilization is also successful
With the previously viable embryos, however, the researchers can already continue breeding the endangered rhinoceros species: “With these nine northern white rhinoceros embryos, the project partners can initiate the next phase of the project – the embryo transfer to surrogate mothers of the southern white rhinos in the Ol Pejeta Conservancy” , so balala. “We are very excited about the offspring from the project who will guarantee the survival of the species.”
Before the now developed embryos can be transferred to females of the closely related rhinoceros, they have to be ready to receive. To find out when this is the case, the scientists want to match the potential surrogate mothers with a southern white rhinoceros bull. This is supposed to indicate the reproductive cycle of the females through its behavior. To do this, however, he must be sterilized so that the potential surrogate mothers in company with the bull do not become pregnant. This is exactly what Hildebrandt and his team did with the rhinoceros bull Owuan. For this purpose, the pachyderm was successfully sterilized using a minimally invasive, non-surgical procedure. In the coming weeks, the bull and the rhinoceros surrogate mothers will be brought together.
Source: Leibniz Institute for Zoo and Wildlife Research (IZW) in the Forschungsverbund Berlin eV