It’s feeding time at the rhino habitat at the North Carolina Zoo in Asheboro. Bonnie, a 5-year-old southern white rhinoceros, trundles to the gate. She shoulders her fellow rhinos out of the way, as her large square jaw hoovers up the pelleted treats.
Bonnie’s gut slurry holds more than just digested lunch: gut bacteria may provide valuable clues for white rhino conservation. Poaching of wild white rhinos coupled with breeding difficulties in captive populations has led the species to be labeled as “near threatened.”
To counter that precarious status, a team of scientists from North Carolina State University and the North Carolina Zoo is probing an unexpected source to better understand the link between those gut microbes and fertility: rhino poop.
The team isolated two groups of microbes that are linked to specific reproductive outcomes. In their study, published in the journal Animal Microbiome in May, the researchers found that one family of microbes is enriched in female rhinos who successfully have given birth, while the other is associated with infertility.
“We always hope that we’re gonna get, you know, like the smoking gun,” says Erin McKenney, an assistant professor of Applied Ecology at N.C. State and co-author of the paper. “But it's not that common, in my experience, where you have one type of microbe that is significantly and consistently enriched for one condition. So that stands out to me that it's a single type.”
If different aspects of the rhino’s health, such as fertility, are associated with specific gut microbes, then this knowledge could help guide therapeutics for rhinos under human care.
A tour of the ‘incredible galaxies that live in us’
The microbiome is a community of microorganisms — like bacteria, viruses, and fungi. They exist virtually everywhere including inside our organs.
“We are humans. We are individual organisms,” McKenney explains. “But we also have our own superhero sidekicks, these incredible galaxies that live in us.”
Gut microbes, in humans and in rhinos, play an important role in maintaining overall body health. Microbes work overtime in the gut, influencing processes like metabolism, nutrient absorption, and immune system regulation.
Christina Burnham, a former graduate student at N.C. State and lead author on the study, says that the southern white rhino microbiome is particularly understudied, suggesting that its microbes could provide a novel source for conservation research.
A tale of two microbes
At the time of the study, the North Carolina Zoo was home to a crash of ten white rhinos. Researchers collected fecal samples from eight of the female rhinos over a six-month period.
Rhinos are creatures of habit and, luckily for the staff of the North Carolina Zoo, they poop in the same spot, everytime.
“They poop in what’s called a midden pile,” says Jb Minter, director of Animal Health and veterinarian at the N.C. Zoo. “It's kind of like your mailbox. They get to come and smell the midden pile. They see who's been there.”
From the large multi-pound plop in the midden pile, only a lentil-sized sample is needed for analysis. The researchers then extracted microbial DNA from the fecal samples in the lab. In the end they were left with a bacterial roll call, detailing all the microbes present in each rhino’s gut.
“They poop in what’s called a midden pile,” says Minter. “It's kind of like your mailbox. They get to come and smell the midden pile. They see who's been there.”
When researchers compared the microbiota based upon fertility, a distinct association emerged. The poop samples revealed a tale of two microbes, each with their own related reproductive outcomes. The rhinos that had successfully given birth at the zoo were enriched in Rikenellaceae microbes, while reproductively unsuccessful rhinos had significantly high levels of a family of bacteria called Mobiluncus.
Rikenellaceae is believed to promote fertility by breaking down a compound found naturally in the rhino’s plant feed. The molecular pathway linking Mobiluncus to infertility is still an area of ongoing research, but the bacteria has previously been associated with poor reproductive outcomes in cows, primates, and even humans.
Poop transplants for conservation
Burnham and McKenney are both careful to note that Mobiluncus and Rikenellaceae are associated with specific reproductive outcomes and it will take more research to establish a causal relationship. Burnham is currently expanding her sample size from the NC Zoo, and has received fecal samples from two other rhino facilities in the U.S. She hopes to gain a more full picture of the microbiome for rhinos under human care.
“With this bigger pool or population size, we'll be able to potentially narrow down a little bit more of these differences in reproductive and non-reproductive animals,” says Burnham.
If this research is able to definitively link Mobiluncus and Rikenellaceae to specific reproductive outcomes, Burnham says that a fecal microbiota transplant (FMT) also known as a poop transplant, could be in the future for these captive rhinos.
“I think it'd be very interesting to see if I took plant material or fecal material from a wild southern white rhinoceros who clearly doesn't have any issues reproducing.” says Burnham. "And I am able to do an FMT to one of our captive rhinoceros that does have issues, over time if I would see differences in the way that the hormones are cycling and differences in the way that nutrients are digested, and that that eventually leads to success and reproduction.”
Poop transplants for animals with unhealthy microbiomes are no longer considered science fiction but are therapies currently being used in zoos across the nation. Minter notes that while the NC Zoo is not currently performing fecal transplants on its rhino population, they have done similar procedures with their antelope to some success.
While there is still a long road before poop transplants are on demand, the answer to white rhino conservation may not be far off; it might be right under their tails.
