Unlike us, flying vertebrates - birds and bats - are not too dependent on symbiosis with the intestinal microflora.
The more we learn about the microflora of our intestines, the more we value it. In recent years, it has become clear how numerous and varied it is, how individual its composition is and how important these bacteria play not only in digestion, but also in maintaining the health of the whole organism. However, this is not true for all animals.
Judging by the results of the new work of American biologists, birds and bats cannot boast of either the number or the diversity of the intestinal microflora. It seems that it is not so important to them even for normal digestion: such is the price for the ability to fly. This is covered in an article published in the mBio magazine.
“When we started the project, we thought to find similarities in the intestinal microflora in animals sharing a similar diet,” says one of the authors of the work, Se Jin Song of the University of California, San Diego. “The idea was that the flight could lead to the selection of certain types of bacteria that are favorable for flying animals. To our surprise, we not only did not find a great similarity between the microflora of birds and bats, but also found that it does not play a big role in their life at all”.
The authors carried out the first and, perhaps, the largest screening of microflora in flying vertebrates - birds and bats. The composition of bacteria was analyzed in fecal samples from 491 bird species and 315 bats. No wonder the article published as a result has several dozen authors - employees of universities, museums, zoos and reserves.
After collecting samples, isolating and sequencing the DNA fragments contained in them, the scientists compared them with information from genetic databases. This made it possible to find out the species composition of the intestinal microflora of animals, which immediately surprised biologists.
Until now, such works have shown that the closer the "hosts" are to each other, the more similar their microbiomes are: developing for millions of years in close symbiosis, they largely determine the development of each other. However, the microflora of bats turned out to be completely uncharacteristic for other mammals, indeed, approaching the microflora of birds. The authors associate this feature, of course, with the ability to fly.
Despite the evolutionary distance that separates bats and birds, despite the fact that they have learned to fly independently of each other, this very difficult task imposes a lot of specific requirements on the animal's organism. In particular, both in those and in other animals there was a shortening of the gastrointestinal tract, and with it the microflora was significantly reduced.
“If you carry the whole mass of bacteria in your gut, it will be quite heavy and will drain some resources,” says Holly Lutz, one of the authors of the new work. "So if your energy needs are extremely high - for example, due to flying - you can't carry all the germs on you, you can't afford to feed them."
As a result, the microflora of birds and bats turned out to be not only few in number, but also unstable, differing greatly even in closely related species. "It was as if they were just taking the first microbes they came across without picking too much," Holi Lutz continues, "and generally not really needing their help."