Scientists have created hybrid white rhinoceros embryos in the lab using frozen sperm from extinct male northern white rhinoceros.
Their work is the latest step in an attempt to bring the most endangered mammal on Earth back from the brink.
Only two female northern white rhinoceros (Ceratotherium simum cottoni) still exist.
The last male northern white rhino, Sudan, died earlier this year.
Thomas Hildebrandt, a global pioneer in reproductive science, has watched the decline of the subspecies of the iconic animal in the past 20 years.
“We may need a little bit of luck, but I think what we can demonstrate already is quite impressive.”
Professor Hildebrandt and colleagues have shown for the first time that artificial reproduction techniques can be successfully used to create rhino embryos, they report in the journal Nature Communications.
They have also proven the ability to generate embryonic stem cells, which could potentially produce more eggs and sperm.
Creating embryos using frozen sperm
Artificial reproduction techniques have never been attempted before in the rhino, study co-author Marilyn Renfree said.
“This is the first time it’s been done in this species because it’s a very large animal and has a particular shape to its reproductive tract,” Professor Renfree of the University of Melbourne said.
About the size of an SUV, the white rhinoceros is the largest of all rhino species.
There are two subspecies: the almost-extinct northern white rhinoceros, and their cousins, the southern white rhinoceros.
Using a specially designed tool, the team harvested eggs from live southern white rhinos and combined them with frozen sperm that had been previously collected from northern white males and stored in sperm banks.
The frozen sperm was a bit sluggish at first, but after zapping it with electricity the team were able to successfully produce early-stage embryos known as blastocysts.
The team also used eggs and sperm from the southern white rhinoceros to create pure embryos.
Three of the early-stage embryos – two hybrid and one pure – have been cryofrozen.
The team plan to implant embryos into southern white rhino females to see if the surrogate mothers can carry a pregnancy to term.
“We have several of these embryos in high quality,” Professor Hildebrandt said.
The quest to create a northern white rhino baby
While this phase of the work aims to create hybrid calves, the goal of the project is to create a pure northern white rhino calf.
To do this, the team plan to harvest eggs from the last two females –Sudan’s daughter Najin and granddaughter Fatu, which live at the Ol Pejeta Conservancy in Laikipia national park in Kenya.
“Before we collect the [eggs] … we need proof of concept that the embryo transfer with hybrid embryos is working,” Professor Hildebrandt said.
It is also unclear at this stage whether or not Najin and Fatu will have viable eggs, he said.
“Nobody has any idea about how they look inside. The younger female is 18, the older female is 26, so we’re running out of time.”
If the team can produce a pure white rhino calf, they could use the stem cell technology, which they used in this paper, to produce a line of northern white rhino eggs from embryonic stem cells.
“We need one or two northern white rhino female calves, then I think we are all go for sure,” Professor Hildebrandt said.
Professor Renfree said the work still had a long way to go, but it was a proof of principle.
“This is a stunning result,” she said.
“I don’t know if it’ll ever save the northern white rhino … but it certainly is a great step in the right direction.”
Should we bring animals back from near extinction?
While powerful in their scope, using artificial technologies to save near-extinct species, such as the northern white rhinoceros is controversial.
Conservation biologist Guy Castley of the Environmental Futures Research Institute at Griffith University applauded the team’s work.
“They’ve made some big strides in advancing what has been known about artificial reproductive technologies and using IVF potentially to rescue genetic material for a species on the brink of extinction,” Dr Castley said, who was not involved in the research.
But, he said, it does not address the bigger picture issues such as poaching and habitat loss that led to demise of the species in the first place.
“If we were able to secure those rhinos they may end up with a life kept in captivity because there’s just no space for them to go in their natural environment.”