Gut microbes help bears gain weight regardless of diet

Everyone knows that Alaskan brown bears are big. Still, different brown bear populations survive on varying diets, so how do these populations achieve similar body weights despite various diets? A team of researchers led by North Carolina State University studied 51 bears in 3 Alaskan National Parks, and found that the secret may lie in the bears’ gut microbiome. 

“We think of bears as having simple digestive tracts, so it’s easy to slip into thinking that they therefore have simple gut microbiomes,” said co-author Erin McKenney. “But this study shows there can be tremendous diversity in the gut microbiomes between individual bears, and that this variation can be very important to the physical condition of these animals.”

“For example, the amount of fat that bears are able to store is absolutely critical to the health of wild populations,” said study co-author Grant Hilderbrand. “If female bears are able to reach levels where 19-20% of their body mass in the autumn is fat, they’ll reproduce. And knowing that they can take different dietary paths to reach those fat levels is a valuable insight.”

“The fact that these populations have distinct diets is valuable, because it allows us to understand the role that the gut microbiome plays in helping bears extract nutrition from very different food sources,” explained study co-author Sarah Trujillo.

“We found that bears benefit from having diverse dietary niches, and the gut microbiome does play a role in extracting nutrition from those diets. Ultimately, that means that the bears in these parks were able to achieve very similar body conditions, despite eating very different things.”

The information gathered from this study is crucial for brown bear preservation. According to Diana Lafferty, the findings can serve as a baseline for future research.

“This study is also important because it gives us a snapshot of bears and their diet in these parks,” said Hilderbrand. “Knowing what bears are eating, and that these diverse diets can all be used to reach similar body conditions, can help us spot emerging challenges for these animals. It can also help us understand how many bears these ecosystems are capable of supporting, even as those ecosystems change.”

“In short, this study has given us significant insights into both the park ecosystems that these bears inhabit, and the microbial ecosystems that help these bears thrive,” said McKenney.

The research is published in the journal Scientific Reports.

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By Erin Moody , Earth.com Staff Writer