Gut microbiomes help bears on vastly different diets reach the same size

A recent study of the gut microbiome of Alaskan brown bears (Ursus arctos) shows that microbial life in the intestines of bears allows them to attain comparable size and fat stores while consuming very different diets. The work sheds light on the role of the gut microbiome in maintaining health in wild omnivores.

“We think of bears as having simple digestive tracts, so it’s easy to fall into the idea that they therefore have simple gut microbiomes,” says study co-author Erin McKenney, an assistant professor of applied ecology at California State University. North Carolina. “But this study shows that there may be great diversity in the gut microbiomes among individual bears, and that this variation may be very important to the fitness of these animals.”

“For example, the amount of fat that bears can store is absolutely critical to the health of wild populations,” says Grant Hilderbrand, study co-author and associate regional director for resources at the National Park Service in Alaska. ‚ÄúIf the bears are able to reach levels where 19-20% of their body mass in the fall is fat, they will reproduce. And knowing that they can take different dietary pathways to reach those fat levels is valuable information.”

For this study, researchers collected fecal samples from 51 adult brown bears in three national parks: Katmai National Park and Preserve, Lake Clark National Park and Preserve, and Gates of the Arctic National Park and Preserve.

Previous research has shown that the diets of bears in each park vary. Lake Clark bears generally eat a lot of berries, salmon, and mammals, such as moose. Bears in the Gates of the Arctic tend to eat seasonal vegetation and mammals, but have less access to fish. And the bears on the Katmai coast have the most diverse nutritional landscape, including a variety of vegetation, fish, and a wide range of marine species.

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“The fact that these populations have different 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,” says Sarah Trujillo, corresponding author of the study and former graduate. student at Northern Michigan University (NMU).

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

“And because parks are well-preserved, protected environments, this study can serve as a foundation for future research,” says study co-author Diana Lafferty, an assistant professor of biology at NMU. “For example, researchers will be able to compare the gut microbiomes of bears in more altered systems, such as areas where bears have more access to garbage and human food, with the data from this study.”

“This study is also important because it gives us a snapshot of the bears and their diet in these parks,” says Hilderbrand. ‚ÄúThe biggest conservation challenge facing us right now is climate change, and understanding what is happening now will help us identify and understand the changes that will come in the future.

‚ÄúKnowing what bears eat, and that these diverse diets can be used to achieve similar body conditions, can help us spot emerging challenges for these animals. It may also help us understand how many bears these ecosystems are able to support, even as those ecosystems change.”

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‚ÄúIn short, this study has given us important information about the park ecosystems these bears inhabit and the microbial ecosystems that help these bears thrive,‚ÄĚ says McKenney.

The study, “Influence of intrinsic and extrinsic factors on the gut microbiome of an omnivore,” will be published September 22 in the open access journal scientific reports. The document was written by Kyle Joly and Buck Mangipane of the National Park Service; Lindsey Mangipane, David Gustine, and Joy Erlenbach of the US Fish and Wildlife Service; and Matthew Rogers of the National Marine Fisheries Service.

The work was made possible by research funding from NMU.

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