Study finds reduced microbial diversity in guts of wild bears that eat
human food

Date:
January 3, 2022
Source:
North Carolina State University
Summary:
A new study suggests that eating human food reduces microbial
diversity in the guts of wild bears.



FULL STORY ==========================================================================
A recent study suggests that eating human food has a pronounced effect
on the microbiome of black bears. Specifically, researchers from North
Carolina State University and Northern Michigan University found that
wild bears who consumed a lot of processed foods had far less diversity
in the microbial ecosystems of their guts.


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"We know a 'western' diet can reduce microbial diversity in the guts of
humans, mice and other species, which can have an adverse effect on their health," says Erin McKenney, co-author of the study and an assistant
professor of applied ecology at NC State. "We want to know if the same
is true for wildlife, particularly given the increasing overlap between
where people live and where wildlife lives. One possibility our work here raises is that if wildlife begin consuming human foods, it may affect
their ability to derive as much nutrition from their traditional, wild
diet if they stop eating human foods." "One step toward seeing if the
same is true for wildlife is to assess the impact that human foods have
on the gut microbiome of wild mammals," says Sierra Gillman, first author
of the study and a Ph.D. student at the University of Washington. "In
this particular study, we wanted to know how human foods influence the
gut microbiome of black bears." Gillman did the work while a grad student
at NMU.

The researchers focused the study on Michigan, which allows hunters to
"bait" bears by leaving out large quantities of human food, such as
sugary cereals and candy. Hunters will bait specific sites for weeks or
months to lure bears to a specific area on a regular basis. As a result,
some bears have a diet that is rich in human junk food for an extended
period of time.

To collect samples from the wild bear population, the researchers
worked with guides who lead scheduled trips with hunters in the Upper
Peninsula of Michigan. The guides collected samples from bears that
were harvested when the guides went on their regularly scheduled trips
with hunters. Specifically, the guides followed a detailed protocol
for retrieving hair samples and two gut samples. The gut samples were
from the jejunum, which is the middle section of the small intestine,
and the colon, which is also called the large intestine.

Ultimately, the researchers were able to retrieve samples from 35 legally- harvested bears.

The researchers processed the gut samples to identify both what kinds
of microbes were present in each bear's microbiome as well as how many
of each type of microbe was present.



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The researchers also conducted a carbon isotope analysis of the bear's
hair, which gave them an assessment of each bear's long-term diet. More specifically, the analysis told researchers the extent to which each
bear was consuming sugar and corn, which are more likely to be found in processed foods.

When analyzing the data, the researchers looked at two measures of gut biodiversity. First they look at the total number of different species
present.

Second, they looked at a measure called Faith's phylogenetic diversity,
which looks at how many different types of species are present.

"Basically, Faith's phylogenetic diversity assesses how many branches
of the bacterial family tree are represented," Gillman says.

Both measures of gut biodiversity were substantially lower in bears that
had been eating more processed foods.

"Essentially, we found that the more human food black bears eat,
and the longer they eat it, the less diverse their gut microbiomes,"
Gillman says "Sugar is very easy to digest," McKenney says. "Lots of
bacteria can consume it. In practical terms, that means processed human
foods actually have lessfood available for bacteria that specialize
in breaking down fiber or other microaccessible carbohydrates. Those
bacterial specialists have trouble competing with the other bacteria
for sugar, and their niche in the food web isn't sustainable if bears
don't eat enough of their traditional diet. We think that's one of the mechanisms for reducing gut microdiversity.



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"And if the gut biodiversity suffers when bears begin consuming more human food, that raises the possibility that it would be more difficult for
bears to derive as much nutritional value from non-human foods if they
return to a 'wild' diet," McKenney says. "Basically, it's not clear how
quickly microbial species that break down fiber, etc., would return."
"Now that we've identified this association between eating human food
and microbial biodiversity, we need to do additional work to determine
what this means for the health of these animals -- and potentially other animals," Gillman says.

"Many hunters use camera traps to monitor their bait sites, and people
we've worked with have told us that they see a wide variety of species
-- raccoons, fishers, martens, deer, hares -- eating the bear bait,"
says Diana Lafferty, co-author of the paper and an assistant professor
of wildlife ecology at NMU.

"It's not clear how baiting might be affecting the microbiomes or
health of other wildlife that is taking advantage of the free food. As
we think about conservation, assessing the impact of our activities on diversity may need to extend to protecting microbial diversity. Because
the evidence increasingly suggests that many of these microbial organisms
are critical to the health of wildlife species. How does baiting fit
into that? Those are issues I think we'll need to explore." The paper, "Human-provisioned foods reduce gut microbiome diversity in American
black bears (Ursus americanus)," is published in the Journal of Mammalogy.

The work was done with support from the National Science Foundation,
under grant 1000263298; and from Sigma Xi, the Scientific Research Honor Society, under grant G2018100198233997.

========================================================================== Story Source: Materials provided by
North_Carolina_State_University. Original written by Matt Shipman. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sierra J Gillman, Erin A McKenney, Diana J R
Lafferty. Human-provisioned
foods reduce gut microbiome diversity in American black
bears (Ursus americanus). Journal of Mammalogy, 2021; DOI:
10.1093/jmammal/gyab154 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220103121728.htm
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