An expansive animal gut microbiome dataset elucidates major compositional shifts across bilaterian evolution
This study introduces the Gut Microbiome Tree of Life (GMToL), a comprehensive dataset of over 17,000 samples from 1,553 species, to reconstruct ancestral gut microbiomes and reveal major evolutionary compositional shifts from Pseudomonadota dominance in early animals to Bacteroidota and Bacillota dominance in tetrapods and birds.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Imagine the animal kingdom as a massive, sprawling library. For a long time, scientists have been reading the "books" (the gut bacteria) of just a few specific sections, like the mammal wing or the bird section. But nobody had ever tried to read the entire library to see how the stories changed from the very first chapter to the present day.
This paper introduces a new, massive project called GMToL (Gut Microbiome Tree of Life). Think of this as a giant, organized map of the library. The researchers gathered a huge collection of 17,366 "book reports" (samples) from 1,553 different animal species, covering everything from tiny insects to giant whales. They pulled these reports from 284 different studies to create one giant, unified picture.
Here is what they discovered by looking at this whole map:
1. The Original Recipe
By using a special "time-travel" method (called ancestral state reconstruction) to guess what ancient animals ate, they found that the very first animal guts were likely dominated by a group of bacteria called Pseudomonadota. You can think of this as the "original flavor" of the animal kingdom's gut.
2. The Great Flavor Swaps
As animals evolved and moved onto land, the "flavor" of their guts changed dramatically, like a restaurant changing its menu over centuries:
- The Tetrapod Shift: When four-legged animals (tetrapods) evolved, the gut menu switched. The original flavor faded, and a new group called Bacteroidota took over as the main ingredient.
- The Mammal & Bird Special: Later, as mammals and birds branched off, the menu changed again. Now, a third group called Bacillota became the star of the show for these animals.
3. Finding the Constants
Even though the menus changed so much, the researchers found some "classic dishes" (core microbes) that have stayed on the menu for a very long time across different animal families.
Why This Matters
This new map doesn't just tell us what happened in the past; it gives scientists a reliable "baseline" or a ruler to measure future discoveries against. It allows researchers to look at an animal they've never studied before and make an educated guess about what its gut bacteria might look like, simply by knowing where that animal sits on the family tree. Essentially, they built the ultimate reference guide to understand how the tiny world inside animals has changed as the animals themselves evolved.
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