North Carolina State University researchers have identified significant differences in the gut microbiome of female southern white rhinos that breed successfully in captivity compared to females that do not breed successfully in captivity. The work raises questions about the role that a particular genus of gut microbes may play in limiting the captive breeding of this species of rhinos.
“Our work focuses on the southern white rhinoceros (Ceratotherium simum simum) because, while not yet endangered, the species’ numbers in the wild are declining due to poaching,” says Christina Burnham, first author of the paper and a former graduate student at NC State.
“There is a significant population of southern white rhinos under human care in the United States, but it has been difficult to ensure that many of these animals reproduce successfully. It is important that we understand why, because farmed rhinos serve as important insurance policies in case wild rhino numbers continue to decline. We wanted to know how the gut microbiome might affect the reproductive capacity of these rhinos.
To do this, the researchers collected several faecal samples from eight female southern white rhinos over a six-month period. The study population consisted of two young; two “sub-adults” who are no longer lactating but not yet of reproductive age; two adults that successfully bred; and two adults that did not reproduce successfully.
“We wanted to have a robust sample size that would allow us to assess the gut microbiome of females of this species while accounting for age, season and reproductive status,” says Burnham.
The researchers extracted and sequenced DNA from the stool samples, which allowed them to identify the diversity and abundance of bacteria in the guts of the study animals.
“We found differences between rhinos in each age group,” says Erin McKenney, co-author of the study and assistant professor of applied ecology at NC State. “In other words, the microbial communities in the gut microbiome change predictably as animals age from juveniles to subadults to adults.
The researchers found that reproductively successful females had less diversity in the types of microbial species present in their gut microbiome compared to the microbiome of reproductively unsuccessful females. The researchers also found that each group of adults hosted microbial species previously associated with reproductive health.
“One of the microbial families we found at significant levels in reproductively successful adults was Rikenellaceae,” says Burnham. “This is interesting because Rikenellaceae has previously been theorized to play a role in helping southern white rhinos break down plant compounds in their diet – including phytoestrogens, which have been linked to limiting reproductive success.”
“On the other hand, we observed a significant enrichment of Mobiluncus microbes only in reproductively unsuccessful adults,” says Burnham. “Previous work has found Mobiluncus to be associated with a range of reproductive health problems in a variety of non-rhinoceros species.”
“However, in these previous studies, Mobiluncus was detected in the cervical and vaginal microbiomes. We only looked at the gut microbiome, the adult women we studied to determine whether Mobiluncus may be present in these microbiomes.
“Because this was a longitudinal study, we collected several samples from each animal over the course of six months,” says McKenney. “And the differences we saw in the gut microbiomes of adult females were consistent over time, suggesting that these differences in microbial communities may play an important role in the reproductive health of these animals. That means we’ll need to do more research to determine what that role might be, if any.”
