This article in Discover on microbiome, or gut biome, comparisons across species was thought- and visual- provoking, wherein the question is why bats & birds appear to have a bacterial desert in their GI tracts:
[Microbiologist Jon] Sanders and his team think there are several possible reasons why birds and bats ended up with such limited, scattershot microbiomes. Both organisms have short, speedy digestive tracts. Maybe their intestines are so efficient that digestive bacteria don’t help much, Sanders says. And many eat insects, a menu that might not make gut bacteria flourish. The fact that other insect-eating mammals, like anteaters, also had somewhat less-defined gut communities backs up this possibility.
It’s also possible fewer gut microbes facilitates flying. “These animals have profound evolutionary adaptations to decrease weight,” Sanders says. Gut bacteria might be heavier baggage than you’d think. Human intestines carry about a pound of bacteria at a time, and in other animals, gut bacteria account for a higher percentage of total weight. For example, if we had as much gut bacteria as a cow, we’d be lugging around nearly 40 pounds of microbiome, Sanders says. That’s enough weight to slow you down, so maybe it’s worth it for birds and bats to drop as much gut bacteria as they can.
Have they evolved to not require the large microbiomes, to even actively reject them? Or is it the act of flying that keeps their microbiomes small? Very unfortunately, they do not address flightless birds.
‘cuz I’m thinking if it’s just the consumption of insects that eradicates the microbiome, I’m going to have third thoughts[1] about becoming an insectivore.
And the visual of being a cow in human form … with 40 pounds of microbiome! It may put a whole other spin on Cordwainer Smith’s concept of the Underpeople[2]!
1 I’ve been having second thoughts about it for years now.
2 If you’re not familiar with the name Cordwainer Smith and have been known to read science fiction, he was one of the finest authors of his era in the field, in my humble opine. No doubt his Chinese background had something to do with his conception of story and myth.
