July 18th, 2013 by James Ayre
New research has confirmed the existence of hologenomic evolution — in other words, the microbes that live within your body (and greatly outnumber your own cells) have now been shown to very likely have exerted influence on the evolution of humans. The new research wasn’t done with people though — so definitive proof of hologenomic evolution in humans will have to wait, though it seems very likely — it was done with three species of jewel wasp.
While the idea certainly makes sense — microbial cells influence, regulate, and affect nearly every process in the body, why wouldn’t they affect evolution? — it has apparently remained a controversial idea since being proposed. But now, the new research has provided proof that it does in fact occur.
The microscopic communities that live within an organisms body are collectively referred to as its microbiome. Research has more and more been making it clear that this microbiome influences everything from brain development, to digestion, to immune system function, and that without it organisms can’t survive. And now, as this new research has shown, the microbiome has been shown to also influence the evolution of its host — direct evidence that these microbes can contribute to the origin of new species by reducing the viability of hybrids produced between males and females of different species.
This research is the strongest evidence to date for “the controversial hologenomic theory of evolution, which proposes that the object of Darwin’s natural selection is not just the individual organism as he proposed, but the organism plus its associated microbial community. (The hologenome encompasses the genome of the host and the genomes of its microscopic symbiotes.)”
“It was a high-risk proposition. The expectation in the field was that the origin of species is principally driven by genetic changes in the nucleus. Our study demonstrates that both the nuclear genome and the microbiome must be considered in a unified framework of speciation,” stated Associate Professor of Biological Sciences at Vanderbilt University Seth Bordenstein who performed the study with post-doctoral fellow Robert Brucker.
The research was conducted with three species of the jewel wasp Nasonia — tiny, match-head sized wasps which parasitize blowflies and other pest flies.
“The wasps have a microbiome of 96 different groups of microorganisms,” said Brucker. “Two of the species they used (N. giraulti and N. longicornis) only diverged about 400,000 years ago so they are closely related genetically. This closeness is also reflected in their microbiomes, which are quite similar. The third species (N. vitripennis), on the other hand, diverged about a million years ago so there are greater differences in both its genome and microbiome.”
“The mortality of hybrid offspring from the two closely related species was relatively low, about 8%, while the mortality rate of hybrid offspring between either of them and N. vitripennis was quite high, better than 90%,” the researchers established.
“The microbiomes of viable hybrids looked extremely similar to those of their parents, but the microbiomes of those that did not survive looked chaotic and totally different,” Brucker continued.
“The researchers showed that the incompatibilities that were killing the hybrids had a microbial basis by raising the wasps in a microbe-free environment. They were surprised to find that the germ-free hybrids survived just as well as purebred larvae. But when they gave the germ-free hybrids gut microbes from regular hybrids, their survival rate plummeted.”
“Our results move the controversy of hologenomic evolution from an idea to an observed phenomenon,” stated Bordenstein. “The question is no longer whether the hologenome exists, but how common it is?”
The new research was just published online in the journal Science.
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