Reproductive success of southern white rhinos linked to gut microbiome

A team of researchers led by the North Carolina State University has recently identified significant differences in the gut microbiome of female southern white rhinos which managed to reproduce successfully in captivity compared to the less successful ones. These findings raise important questions about the role particular types of gut microbes may be playing in limiting captive breeding of this species.

“Our work focuses on the southern white rhinoceros (Ceratotherium simum simum), because while it is not yet endangered, species numbers are declining in the wild due to poaching,” said study lead author Christina Burnham, a former graduate student in Animal Sciences at NC State.

“There is a significant population of southern white rhinos under human care in the United States, but there have been challenges in getting many of these animals to reproduce successfully. It is critical we understand why, as the managed rhinos serve as important assurance populations in case wild rhino numbers continue to fall. We wanted to know how the gut microbiome may influence the reproductive ability of these rhinos.”

How the research was conducted

To clarify these issues, the scientists collected multiple fecal samples from eight female southern white rhinos during a period of six months. The examined population consisted of two juveniles, two “subadults” that are no longer nursing but have not yet reached reproductive age, two adults that have managed to reproduce successfully, and two that have not reproduced successfully.

“We wanted to have a robust sample size that would allow us to assess the gut microbiome of females in this species while accounting for age, the time of year and reproductive status,” Burnham explained.

What the researchers discovered 

By extracting and sequencing DNA from the fecal samples, the experts identified the diversity and abundance of bacteria in the gut of the female rhinos. The analysis revealed important differences between animals in each age group, suggesting that microbial communities in the gut microbiome change predictably as the animals grow, reflecting changes in their diet and behavior.

However, the differences in bacterial populations in the reproductively successful versus unsuccessful adults provided clear evidence of the critical role of the microbiome in reproductive processes. The researchers found that reproductively successful females had less diversity in the types of microbial species in their gut microbiome compared to the unsuccessful ones. Moreover, each group of adults was hosting microbial species which have been previously associated with reproductive health.

“One of the microbial families we found at significant levels in reproductively successful adults was Rikenellaceae,” Burnham reported. “This is of interest because Rikenellaceae has previously been theorized to play a role in helping southern white rhinos break down dietary plant compounds – including phytoestrogens that are associated with limiting reproductive success.”

“On the other hand, we only saw significant enrichment of Mobiluncus microbes in reproductively unsuccessful adults. Previous work has found that Mobiluncus is associated with a range of reproductive health problems in a variety of non-rhinoceros species.”

Further research is needed 

Since in those previous studies, Mobinculus was detected in cervical and vaginal microbiomes, further research is needed to clarify whether this is the case in rhinoceros females too.

“Because this was a longitudinal study, we collected multiple samples from each animal over the course of half a year,” said co-author Erin McKenney, an expert in Applied Ecology at NC State. “And the differences we saw in the gut microbiomes of adult females were consistent over time, which suggests that these differences in microbial communities may be playing an important role in the reproductive health of these animals. That said, we will need to do additional research to determine what that role may be, if any.”

More about Southern white rhinos 

Out of all five rhino species, the Southern white rhino is the only one that is not classified as endangered. Thanks to extensive conservation efforts, the Southern white rhino is now classified as “near threatened.”

Key points

Physical characteristics

Southern white rhinos are the second largest land mammals after elephants. They can grow to be 12-13 feet long and 6 feet tall at the shoulder, and can weigh up to 2.5 tons. They are known for their square-shaped lip, which differentiates them from black rhinos, which have a hooked lip. They have two horns, with the front one typically larger than the other, that can grow up to 5 feet long.

Habitat and distribution

These rhinos are native to southern Africa. They mainly live in South Africa, but they have also been reintroduced to Botswana, Namibia, Zimbabwe, and Swaziland. They prefer habitats with plenty of grass for grazing and water holes for wallowing.

Diet

Southern white rhinos are herbivores and primarily eat grass, making them grazers. They use their broad, square-shaped lip to help them eat large quantities of grass.

Behavior

These animals are generally quite social and live in groups known as “crashes,” which typically consist of a female and her calves, though larger groups can sometimes be found. Male southern white rhinos are generally solitary unless there’s a female in heat nearby.

Conservation status

In the early 20th century, southern white rhinos were thought to be extinct, but a small population was discovered in South Africa. Since then, rigorous conservation efforts have helped to increase their numbers. However, they are still threatened by poaching for their horns, which are prized in traditional Asian medicine, and by habitat loss.

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By Andrei Ionescu, Earth.com Staff Writer

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