Gut Microbiomes Help Bears With Very Different Diets Reach the Same Size

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

“We think bears have a simple digestive tract, so it’s easy to think that they therefore have simple gut microbiomes,” says Erin McKenney, study co-author and assistant professor of applied ecology at North Carolina State University. “But this study shows that there can be tremendous variation 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 bears can store is absolutely critical to the health of wild populations,” said Grant Hilderbrand, co-author of the study and deputy regional director for resources at the National Park Service in Alaska. “By the fall, when female bears reach a level where 19-20% of their body weight is fat, they will reproduce. And knowing that they can take different dietary routes to get to those fat levels is a valuable insight.”

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 bear diets vary from park to park. Bears at Lake Clark generally eat a lot of berries, salmon, and mammals like moose. Bears in the Gates of the Arctic tend to eat seasonal vegetation and mammals, but have less access to fish. And bears on the Katmai coast have the most diverse food landscape, including a variety of plants, fish, and a variety 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 food from vastly different food sources,” says Sarah Trujillo, corresponding Study author and former graduate student at Northern Michigan University (NMU).

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

“And because the parks are protected, well-preserved environments, this study can serve as a basis for future research,” says Diana Lafferty, co-author of the study and assistant professor of biology at NMU. “For example, researchers will be able to compare the gut microbiomes of bears in more disrupted systems — such as areas where bears have more access to litter and human food — to 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. “The biggest conservation challenge we are currently facing is climate change, and understanding what is happening now will help us see and understand any changes that will take place in the future.

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“Knowing what bears eat and that these different diets can all be used to achieve similar body conditions can help us identify new challenges for these animals.” It can also help us understand how many bears can support those ecosystems even as those ecosystems change.”

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

The study “Intrinsic and extrinsic Factors Influence on an Omnivore’s Gut Microbiome” is published in the open access journal Scientific Reports. The paper was co-authored 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 the NMU.


Note to the editor: The study summary follows.

“Intrinsic and extrinsic factors influence the gut microbiome of an omnivore”

authors: Sarah M. Trujillo and Diana JR Lafferty, Northern Michigan University; Erin A McKenney, North Carolina State University; Grant V Hilderbrand, Kyle Joly, and Buck A Mangipane, National Park Service; Lindsey S Mangipane, David D Gustine, and Joy A Erlenbach, US Fish and Wildlife Service; and Matthew C. Rogers, National Marine Fisheries Service

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Released: September 22nd Scientific Reports

DOI: 10.1038/s41598-022-19527-4

Abstract: The internal mechanisms responsible for modulating physiological state, particularly those performed by the gut microbiome (GMB), are still underexplored in wild animals. However, as there are latitude and seasonal shifts in resource availability, the myriad microecosystem services supported by the GMB can be particularly important to wildlife health and resilience. Here we use brown bears (Ursus arctos) as an ecological model for quantifying the relationship between body condition metrics of wild animals, commonly used to assess individual and population health and the composition and structure of the GMB community. To achieve these goals, we undersampled brown bear fecal samples collected during United States National Park Service research activities at three national parks and reserves (Katmai, Lake Clark, and Gates of the Arctic) and analyzed microbial DNA for 16S rRNA -Amplicon sequencing and microbial taxonomy extracted classification. We analyzed GMB communities using alpha diversity indices and then used Spearman’s correlation analysis to examine the relationships between alpha diversity and health metrics for brown bears. We found no differences in GMB composition between bears with different body conditions, nor any correlations between alpha diversity and body condition. Our results indicate that GMB composition reflects different foraging strategies while allowing brown bears to achieve similar body condition outcomes.

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