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The last two known living northern white rhinos, both female, at Ol-Pejeta Conservancy in Kenya. Photo: Tony Karumba/AFP/Getty Images

Scientists hoping to save the most endangered mammal in the world — the northern white rhinoceros — may have found a way using assisted reproduction technologies (ARTs). Researchers announced Wednesday in Nature Communications that they developed the first hybrid rhinoceros embryo that is ready to be implanted into a surrogate rhino.

Why it matters: There are only 2 northern white rhinos left in the world —both female — after poaching, habitat loss and other factors have caused them to virtually disappear from their African home. Scientists are increasingly turning to creative methods like ARTs to try and save them.

"The northern white rhinoceros didn't fade from evolution, it faded because it wasn't bullet-proof."
— Thomas Hildebrandt, study author, Leibniz Institute for Zoo and Wildlife Research

What they're doing: The scientists are creating hybrid rhino embryos because Kenyan authorities have not yet allowed them to collect eggs from the 2 remaining northern white rhinos. Dvůr Králové Zoo's Jan Stejskal, another study author, says they hope to get permission within 3 to 4 months so they would be able to create pure northern white rhino embryos.

The hybrid embryos allow scientists to make advances toward potentially saving the subspecies.

  • The hybrid embryos combine northern white rhino semen with eggs from southern white rhinos, a closely-related subspecies.
  • They plan to use the hybrids to test implantation techniques before they actually create pure northern white rhino embryos. Plus, Hildebrandt adds, "We think the hybrid will also play a crucial role in the future as a surrogate, because it's much closer to the pure breed."
  • Their long-term plan, though, is to breed pure northern white rhinos.

The big picture: Following a roadmap laid out in 2016, multiple simultaneous research efforts are focused on 2 main high-tech methods for saving pure northern white rhinos:

1. Harvesting eggs from the 2 live rhinos and inseminating them with frozen sperm for in vitro fertilization into a surrogate rhino (as this study has started, albeit with hybrids). This is closer to being accomplished, although challenges remain.

2. Developing stem cells from frozen skin cells of pure northern white rhinos to create embryos and implant them. Barbara Durrant, director of reproductive sciences at San Diego Zoo Global, says they have a Frozen Zoo with living cell lines, gametes, and embryos of various animals, including 12 cell lines of the northern white rhino.

  • Durrant says they examined the cell lines recently and discovered "good news — there's a lot of genetic diversity, even more than in the southern white rhinos." She points out that harvesting the eggs from the remaining rhinos would offer a limited genetic pool, particularly since they are mother and daughter.
  • This method is expected to take about a decade to develop, but Hildebrandt says the recent growth in regenerative medicine may speed this up.
"The main goal is to have a pure northern white rhino. It doesn't matter if it goes through stems cells or through the harvest of oocytes [immature eggs cells] of the last living donors," Stejskal says.

Be smart: If a hybrid is successfully born, one concern is whether it will be able to propagate or if it will be similar to a mule (a horse-donkey mix that's unable to reproduce), according to Jeanne Loring, a professor at the Scripps Research Institute who conducts stem cell research.

"While there's value in both approaches, once you hybridize, there will no longer be a northern white rhino," Loring says.

Other advances: Loring, who collaborates with the San Diego Zoo, says her research team already has developed the stem cells for the northern white rhino and is in the process of developing artificial gametes to produce eggs and sperm.

  • "In theory, if we can make artificial gametes... then we can do crosses within the same species, not making a hybrid," Loring says.
  • One big contribution from the study published Wednesday, Loring says, is that the researchers fine-tuned the IVF procedure so they are "confident" that if they can develop viable lab-made gametes, they will know how to best implant them.

The controversy: Some question whether scarce resources are being wasted, especially when the environment has not changed enough to protect currently living animals. Jo Shaw, African rhino lead for WWF International, said in a statement:

“The real fight for the survival of northern white rhinos in their natural habitat was lost over a decade ago...[W]e must learn from the sad lessons of the past and ensure we are bold and act decisively before this becomes a reality for any of the remaining five species of rhinos. Large mammals, like rhinos, should be seen as symbols of large functioning ecosystems and [ARTs] have limited value unless there are safe places for populations to thrive.”

Others, like the Cincinnati Zoo's Terri Roth, argue that the money for ART and the funding streams for conservation are separate. In other words, we can do both.

Ultimate goal: Durrant tells Axios the zoo's long-term goal, which could take dozens of steps including controlling poaching, is:

"To have a herd of northern white rhinos reproducing and sustaining themselves back in their African habitat."

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