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As birds migrate, the microbes in their gut evolve

As birds migrate, the microbes in their gut evolve
Researchers found that bird microbiomes change with their environment as they move from place to place, according to a study with Kirtland's warblers, pictured. Photo by Nathan W. Cooper

Sept. 28 (UPI) -- The community of microbes living in a person's intestines is influenced by their physical and mental health, as well as their dietary habits. It's also dictated by location.

The gut microbiome of someone living in Arizona will be different than the gut microbiome of someone residing in South Carolina. The same is true for birds -- and even more so, according to scientists at the University of Chicago.

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New research, published Tuesday in the journal Molecular Ecology, suggests the gut microbiota of migratory birds evolves as they move from place to place.

"We've seen in other animals that microbiomes can be influenced by the places their hosts live," lead study author Heather Skeen said in a press release.

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"Lots of birds migrate, and they experience different environments at different points of their migratory cycle. We didn't know how these different environments affected the birds' microbiomes," said Skeen, a doctoral student at the Field Museum and the University of Chicago.

For the study, Skeen and her colleagues attached tracking devices to Kirtland's warblers flying from the Bahamas to Michigan for the summer.

Before the birds were released and headed north, scientists placed each Kirtland's warbler into a brown paper bag, where the birds promptly relieved themselves. Researchers sequenced the microbiota found in the droppings of each bird.

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The tracking devices allowed researchers to find and capture the same birds once they arrived in northern Michigan. Scientists collected and analyzed the droppings from the same individual birds and compared the microbiota from the two sample sets.

Their analysis showed each bird's gut microbiome is heavily dependent on geography.

"One of the most important parts about this study is that we were able to recapture birds at different portions of the annual cycle in different locations, and we have this one-to-one comparison of the same population and the same individuals and how their microbiomes changed," Skeen said.

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"If we'd tested different individual birds, we wouldn't have been able to say for sure if the changes we saw were due to location or if they were just differences between populations. Since we were looking at the exact same birds, these results are much more supported," Skeen said.

With other migratory birds, the study might not have gone as smoothly, but Kirtland's warblers are unique.

The tracking devices were helpful, but even if they had failed, researchers knew where the birds were headed. That's because the small yellow-breasted song birds only breed in young jack pine forest.

"We picked Kirtland's Warbler because there are very, very few species of birds where you would have been able to track individual birds from their non-breeding grounds and then capture them on their breeding grounds," said Skeen.

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Several weeks after the birds left the Bahamas, their trackers started pinging radio towers in northern Michigan.

"When one of our birds' trackers pinged near a tower, we would drive around the range using a handheld radio antenna, looking for the bird," Skeen said. "Once we picked up the signal, we got out of the car and walked around, trying to attract the birds using recordings of their songs."

By studying how the microbiomes of birds change from place to place, scientists hope to better understand how the avian microbiome functions. Previous studies suggest the avian microbiome is quite different than the mammalian microbiome.

Among mammals, an individual's gut microbiome is strongly correlated with the animal's species and lineage, but the microbiota in bird's intestines are much less stable and more easily influenced by environmental changes.

The latest study suggests large groups of bacteria are transient, having little impact on a bird's microbiome. These food-borne microbes pass right through a bird's inside, never colonizing it's intestines.

Understanding the idiosyncrasies of the avian microbiome could ultimately help researchers better anticipate their ability to adapt to climate change.

"An animal's gut microbiome is an additional level of molecular diversity, and as global climate change alters ecosystems, the gut microbiome might be one of the avenues in which animals can adapt to the changing environment," Skeen said.

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"The gut microbiome has its own unique ecosystem, and it's ripe for discoveries," Skeen said.

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