We live in a microbial world – one brimming with little microorganisms unseen by our limited vision. They reside all over the place, from boiling hydrothermal vents to the skins of fish to inside our digestive tracts. They are incredibly diverse, some of which contribute to human health, others of which sap us of our vitality.
But humans are by no means alone in harboring gut microbes – birds, reptiles, amphibians, and mammals all have gut bacteria. One creature, however, has flown from expectation with a unique microbiome pattern for a mammal: bats.
Rather than following the trajectory of their closest mammalian relatives, bat guts instead mimic the bacterial unpredictability of birds. To uncover this surprising detail, the team probed deep inside the bowels of Ugandan and Kenyan caves to collect bacteria samples from the skin, tongues, and guts of 497 African bats across 31 different species.
The team then extracted DNA from individual cells in order to grab a "barcode" of the bacterial communities within the samples and compared the "barcodes" of 900 vertebrate species to see how they lined up in relation to one another. Unlike most mammals, bats are not that reliant on their gut flora. There were more species living on their skin and in their mouths than in their stomachs. In fact, different species of bats can have vastly different bacteria from one another.
"There’s essentially no relationship between the bat microbiome and bat evolutionary history," said lead author Holly Lutz, a research associate at Chicago’s Field Museum and post-doctoral researcher at the University of California, San Diego, in a statement provided to IFLScience. "You’d expect to see similar microbiomes in closely-related bat species if these animals depended strongly on their bacteria for survival. This is largely what we’ve seen in other mammals that have been studied, but it’s just not there in bats."
The finding suggests flight may drastically change the microbes in their tiny tummies. As the only mammal that can fly (unaided by aircraft), the team suggests that lifestyle became a governing factor for these mammals, especially as birds and bats are not closely related – they evolved the ability to fly independently of each other.
"It's almost like they're just picking up whatever's around them and they don't really need their microbes to help them in ways that we do," said Lutz, whose team's paper is published in mBio.
"It shifts the paradigm we’ve been operating under, that animals require microbes for digestion and nutrient acquisition. That’s true for us, but it may not be true for all species," she added. "The trends we’re seeing suggest that bats may not depend on bacteria the same way many other mammals do, and that they can survive just fine without a strict suite of bacteria in their guts to help them digest their food."
A long digestive tract would likely weigh the bats down, and it’s possible that the high energetic demands of flight outweigh the benefit of certain gut bacteria. While the human microbiome is filled with trillions of bacteria, making up around 1 percent of our body weight, bats have extremely short guts. Food zooms through in 15 to 20 minutes.
"For bats, you can’t be carrying around non-essentials," said Lutz. "You need to reduce weight for flying – you don’t want a heavy gut."
Such knowledge is not irrelevant or purely trivia fodder; it could be vital to the preservation of species around the world.
"Bats may be very susceptible to environmental change – if they have a transient microbiome, they might not have the most stable defense mechanisms," said Lutz. “Human-caused disturbances to the environment are a very important issue. Bats may be extra-fragile and more at risk."