Can lab-grown embryos save the northern white rhino from extinction?
After the death of Sudan, the world’s last male northern white rhinoceros, scientists have grown embryos containing DNA of his kind
Months after the death of Sudan, the world’s last male northern white rhinoceros, scientists said they have grown embryos containing DNA of his kind, hoping to save the subspecies from extinction.
With only two northern white rhinoceroses known to be alive today – both infertile females – the team hopes their breakthrough technique will lead to the re-establishment of a viable northern white rhino breeding population.
“Our goal is to have in three years the first NWR calf born,” Thomas Hildebrandt, head of reproduction management at the Leibniz Institute for Zoo and Wildlife Research in Berlin, said on Wednesday.
“Taking into account 16 months [of] pregnancy, we have a little more than a year to have a successful implantation.”
The team’s work, using a recently patented, two-metre (6.6-foot) egg extraction device, resulted in the first-ever test tube-produced rhino embryos.
Now frozen, these “have a very high chance to establish a pregnancy once implanted into a surrogate mother”, Hildebrandt said.
The hybrid embryos were created with frozen sperm from dead northern white rhino males and the eggs of southern white rhino females, of which there are thousands left on Earth.
The eggs were harvested from rhinos in European zoos.
The team now hopes to use the technique to collect eggs from the last two northern white rhinos – Najin and Fatu, the daughter and granddaughter of Sudan, who died in March at age 45. They live in a Kenyan national park.
By fertilising these with northern white rhino sperm and implanting the resulting embryos in surrogate southern white rhino females, the team intends to create a new, fledgling northern white rhino population.
“Our results indicate that ART [assisted reproduction techniques] could be a viable strategy to rescue genes from the iconic, almost extinct, northern white rhinoceros,” the team wrote in the journal Nature Communications.
The researchers have sought permission to harvest eggs from Najin and Fatu in Kenya, hopefully before the end of the year.
But the procedure is not without risk.
“We have to do a full anaesthesia, the animal is down for two hours, and it is quite a risky situation” for the last two of their kind, Hildebrandt said.
“We are highly afraid something unexpected would happen that would be a nightmare.”
In the meantime, the team will practice, implanting some of their hybrid embryos into southern white rhino surrogates “to test the system”.
Any hybrids born as a result may play a crucial future role as surrogates, sharing more genes with northern rhinos than purely southern surrogates.
There is, however, a key obstacle to the team’s envisaged northern white rhino repopulation.
With only two northern white rhino females left and all the available semen from only four dead males, assisted reproduction techniques alone would likely lead to a population without the genetic diversity required for a species to thrive.
To this end, the researchers hope to use stem cell technology to engineer eggs and sperm from the frozen skin cells of 12 dead northern white rhinos that were unrelated to one another.
“This would enlarge the founding diversity of the future NWR population substantially,” the team said in a statement.
There is time pressure, they pointed out, with only two animals still around to socialise the babies in the mysterious ways of northern white rhinos.
“It is a motivating aspect to succeed as soon a possible so the calf that we produce can grow up with Najin and Fatu,” Hildebrandt said.
Terri Roth and William Swanson of the Cincinnati Zoo and Botanical Garden, in a comment on the study, said assisted reproduction techniques alone cannot save a species from extinction.
“Impressive results in a Petri dish don’t easily translate into a herd of healthy offspring,” wrote the duo, who are not involved in the research.
“Achieving the latter requires navigating an untrodden path fraught with obstacles, and it remains unlikely that a viable population of northern white rhinos will be restored.”
For the researchers, however, a combination of assisted research techniques and stem cell techniques could “provide a blueprint on how to save highly endangered species that have already dwindled to numbers that make conventional conservation efforts impossible”.