You are not just yourself. You are also the thousands of microbes that you carry. In fact, they represent an invisible majority that may be more you than you realize. These microscopic¹ fellow travelers are collectively called the microbiome. Realization² that every species of plant and animal is accompanied by a distinctive³ microbiome is old news. But evidence of the impact that these microbes have on their hosts continues to grow rapidly in areas ranging from brain development to digestion⁴ to defense⁵ against infection to producing bodily odors.

 

Now, contrary to current scientific understanding, it also appears that our microbial companions play an important role in evolution. A new study, published online on July 18 by the journal Science, has provided direct evidence that these microbes can contribute to the origin of new species by reducing the viability⁶ of hybrids⁷ produced between males and females of different species.

 

This study provides 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 encompasses⁸ 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 genetic⁹ changes in the nucleus¹⁰. Our study demonstrates that both the nuclear genome and the microbiome must be considered in a unified¹¹ framework of speciation," said Associate Professor of Biological Sciences Seth Bordenstein who performed the study with post-doctoral fellow Robert Brucker.

 

They conducted their research using three species of the jewel wasp¹² Nasonia. These tiny, match-head sized wasps¹³（黄蜂） parasitize blowflies and other pest flies, which make them useful for biological control.

 

"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 diverged¹⁴ about 400,000 years ago so they are closely related genetically¹⁵. 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, he explained.

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