Can hybrid embryos save the white rhinos from extinction?
The northern white rhino population is in jeopardy
The northern white rhino is one of the animal kingdom’s many majestic giants, but years of poaching has taken a toll on their population. From 1970 to 1980, their numbers plummeted from 500 to 15 as illegal hunters pursued white rhinos for the ivory of their horns.
Things started to turn around during the 1990s and 2000s, groups and individuals began to crack down on poachers within the white rhinos’ range. As a result, the population of white rhinos in the wild recovered slightly, peaking at around 32 individuals.
Since 2003, the rate of white rhino poaching has been on the rise and has affected the animals’ numbers. As of 2008, northern white rhinos have been declared extinct in the wild, and in 2018, the last male northern white rhino died. Now, there are only two of these magnificent beasts left on Earth. Both of them are females.
Critically endangered (possibly extinct in the wild)
Najin and Fatu are the last two northern white rhinos in existence. They live at the Ol Pejeta Conservancy in Kenya, and they could be the species’ last hope for the future. In 2014, keepers in the Czech Republic collected sperm samples from a male northern white rhino living in their care.
Those samples were frozen and stored, and later, they were used in an attempt to breed Najin and Fatu. Both attempts at inducing pregnancies in the two female rhinos were unsuccessful, forcing scientists to consider new methods of approach for saving the white rhinos from extinction.
It is with great sadness that Ol Pejeta Conservancy and the Dvůr Králové Zoo announce that Sudan, the world’s last male northern white rhino, age 45, died at Ol Pejeta Conservancy in Kenya on March 19th, 2018 (yesterday). #SudanForever #TheLoneBachelorGone #Only2Left pic.twitter.com/1ncvmjZTy1
— Ol Pejeta (@OlPejeta) March 20, 2018
Typically, when a species is placed on the endangered list, a recovery plan is established by whatever local conservancy group oversees the population. From there, breeding programs of captive individuals are used to begin bolstering the number of individuals on the planet.
When healthy breeding populations have been established, in most cases, reintroduction begins. Small populations of the species are released into the wild to begin repopulation. However, in the case of the northern white rhinos, scientists and conservationists alike have been stuck at step two for decades.
Finding a workaround
Unwillingness and inability to breed aren’t uncommon among captive species and individuals, and in most cases, zoos can jockey animals around until a pair matches and produces offspring. In the case of Najin and Fatu, the options for procreation are far more limited. Even the fallback of artificial insemination isn’t working for them, so what are scientists to do?
We’ve revived entire species from the dead before, but it has never been an easy task. Fortunately, the world of reproductive sciences has been evolving quickly, and conservationists and animal experts now have myriad options to choose from when it comes to creating new life.
Neither surviving female is healthy enough to birth live young. Aside from that, there is the added challenge of finding an option that preserves the northern white rhino genome while maintaining high enough levels of viability.
An international consortium of scientists & conservationists from @IZWberlin @kwskenya @zoodvurkralove @BioResource @olpejetaconserv successfully harvested eggs from the only two remaining northern females who live in Ol Pejeta to try save the species #SavetheNorthernWhiteRhinos pic.twitter.com/94klYUHfQp
— County Government of Laikipia (@LaikipiaCountyG) August 23, 2019
One possible route to repopulation involves approaching conventional methods from a new and enlightened angle. Although neither Najin nor Fatu can bear young, they both still produce viable egg cells, which can be harvested, frozen, and kept in a lab.
Much like humans undergoing fertility therapy or other conception aids, the grandmother-granddaughter pair or northern white rhinos can hope for success through in-vitro fertilization. This method of conception combines sperm and multiple egg cells in an external environment before implanting them in a host mother.
By using multiple eggs during the in-vitro process, the chances for success, even in females with fertility issues, is significantly increased. In some fortunate cases, the method is so effective, and it results in multiple pregnancies. Once the sperm has fertilized the eggs, the cells are transferred to a living host.
Doing things the old-fashioned way
While Najin and Fatu may not be the physical mothers of any of their calves, modern reproductive science has made it possible for their genes to be passed on to another generation.
How? with modern science, a surrogate mother from the thriving population of southern white rhinos could become the mother to their children. The two types of animals have similar enough reproductive organs and their eggs could be used in place of Najin or Fatu’s.
While the animals are compatible, gathering eggs from them is a far more complicated procedure.
Researchers working on bringing back the northern white rhinos have managed to gather a few eggs so far, but not nearly enough to repopulate an entire species.
It’s no secret that rhinoceroses are large animals. Just as cattle and horses have significantly larger hearts than we humans do, rhinos have much larger reproductive organs. Locating and withdrawing eggs from a rhino’s ovaries is a far greater ordeal than it is for humans.
To complicate matters further, the ovaries of a southern white rhino are located three to four feet from her rump, and the veterinarian seeking to collect the eggs must guide a probe that distance up her rectum and into an ovary before using a catheter to remove the eggs.
The procedure is anything but easy. In addition to the difficulty involved in the process of extracting eggs, the success rate of current methods is hardly ideal. Researchers working on bringing back the northern white rhinos have managed to gather a few eggs so far, but not nearly enough to repopulate an entire species.
The odds of reestablishing a sustainable population of northern white rhinos through in-vitro fertilization and surrogacy currently seem pretty slim. Fortunately for the rhinos, science has a few other methods up its sleeve.
In the last decade, stem cell research has gone from a thing of whimsy to an advanced field of study that continues to improve by leaps and bounds with every passing year. Its applications are seemingly endless, and they just might be the answer that the northern white rhino conservationists have been looking for.
Stem cells are sort of like biological canvases. They come in different varieties: Totipotent, pluripotent, multipotent, oligopotent, and unipotent. Each of these types has unique limitations and can be found in various sources from embryonic tissue to adult bone marrow.
To make baby rhinos, scientists have been focused on induced pluripotent stem cells, which are gathered and grown from the skin of adult white rhinos
A cell from your bicep and a cell from your gametes (sperm or egg) both hold the same blueprints; they just come in different packaging.
Pluripotent cells behave similarly to embryonic stem cells, which can be coaxed into becoming just about any other type of cell. In this case, even though the original cells were taken from the skin of adult rhinos, they can be trained to become something different, such as egg cells.
Using what knowledge we currently have of stem cells and their manipulation, scientists can tell a northern white rhino’s skin cell to become a viable egg or sperm cell. From there, they can attempt in-vitro fertilization and implantation into a surrogate, even without fertile parents.
The method is still in its infancy, but it has been successfully carried out more than once.
Increasing population through embryos
With stem cells as a backup and surrogates abound, Najin and Fatu have plenty of options. In late 2019, conservationists and rhinos alike received promising news. Eggs gathered from the two northern white rhinos had been fertilized and resulted in successful embryos. Those embryos were frozen in liquid nitrogen and prepared for a long journey.
Waiting down in southern Africa are the lucky mamas who will become the surrogates for the next generation of northern white rhinos. The embryos have quite a ways to travel before they can be implanted. After that, they can grow within their new mother for the 16 to 18-month gestation period typical of white rhinos.
Although the methods of creating viable embryos are currently long, challenging, and not terribly efficient, these babies-to-be are incredibly promising first steps. In addition to the two successful in-vitro attempts in September, December of 2019 saw the creation of a third viable embryo.
2020 will undoubtedly see further attempts at creating more embryos. With luck, we can soon hope to hear news of successful implantations in surrogate moms. In 2021, we can throw a worldwide baby shower for some bouncing baby northern white rhinos, whose births will serve as a beacon of hope for a dying species.
A deeper dive — Related reading from the 101:
- Will scientists use skin to resurrect the extinct Tasmanian tiger? | Science 101
New breakthroughs in stem cell research have opened doors to reviving animals not seen in decades.
- Animal Frankensteins: 25 Animals That Combined Their Genes to Form Bizarre Hybrids | Science 101
Hybrids are nothing new, but that doesn’t mean they can’t still be surprising!