Evolution: one size does not fit various microbiomes (Introduction)

by David Turell , Tuesday, April 14, 2020, 21:14 (1682 days ago) @ David Turell

Human microbiome research findings do not fit lots of other species:

https://www.quantamagazine.org/why-is-the-microbiome-important-in-some-animals-but-not-...

"But the human example is not a good model for what’s going on in a diverse range of species, from caterpillars and butterflies to sawflies and shrimp, to some birds and bats (and perhaps even some pandas). In these animals, the microbes are sparser, more transient or unpredictable — and they don’t necessarily contribute much, if anything, to their host. “The story is more complex,” said Sarah Hird, an evolutionary biologist and microbial ecologist at the University of Connecticut, “more fuzzy.”

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"So it’s not such a leap to think there could be animals that don’t have such relationships at all, or that have relationships that play by different rules. “I think there’s now an increasing realization that there’s this whole spectrum of kinds of associations that you might find,” Agashe said.

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“'There’s a whole range of different kinds of lifestyles that are going to be really complicated.” Perhaps the transient, low-abundance microbes are doing something more nuanced, or perhaps they represent an early step in the formation of a more stable evolutionary relationship. Maybe they remain neutral most of the time and only become functional in certain contexts. Some researchers, for instance, posit that these microbes could protect a host from infections simply by taking up space in the gut and blocking out pathogens. Furthermore, bacteria that have adapted to a toxic plant or other hazard might be helpful even if they’re acquired just temporarily, without ever engaging in a formal symbiosis.

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“'If you think about it, there’s lots of reasons not to have an established microbiome,” Agashe said. “It’s actually not surprising that there are animals that have gone a different route. … But the key thing is, we don’t know why” — what factors lead to and enable the formation and maintenance of a microbiome, and conversely, what factors might prevent those relationships.

"Caterpillars, dragonflies, certain ants and other animals provide a way to investigate the potential disadvantages of long-lasting symbiotic relationships with live-in microbes; such disadvantages tend to be difficult to measure and test. Researchers suspect that these animals might be selectively avoiding certain potential penalties of symbiosis: Bacteria might compete with their host for nutrients, for instance, or aggravate the immune system.
For some animals, those risks might outweigh the potential benefits. If they have already evolved whatever enzymes or behaviors they need to live on their own, they’re no longer bound by selective pressures to acquire a microbiome.

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"...the findings illustrate that there’s much to learn by comparing species — and that there’s much to lose by making premature assumptions about what their relationships with bacteria might look like. At the very least, this means proceeding with greater caution when translating studies done in flies, mice and other model organisms to humans. (Already, significant differences have been found in the gut microbiomes that develop in wild mice versus lab-bred mice — and the former have often proved to be a more accurate model of how certain experimental drugs might function in humans.)

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"Scientists’ emerging awareness of the diverse relationships that animals share with microbes “should make us really cautious about drawing inferences using fruit flies as models for gut microbiome importance or interactions, because fruit flies might be operating from a very different fundamental starting point compared to humans. It’s the same thing with mice.'”

Comment: Bacteria are still here to be helpful in certain microbiomes, where ever they are needed. They are not needed everywhere is the point of this paper. The answer to why or why not needs much more major research.