There are many questions surrounding the relationship between the functioning of our human body and the presence of the microbes that live in and on us. The current state of knowledge does not allow us to fully understand what impact our microbiota has on our lives. To approach this question, it is important to find out how our gut metagenome interacts with our own genome.
On July 18th, 2013, Science Magazine published an interesting paper called “The Hologenomic Basis of Speciation: Gut Bacteria Cause Hybrid Lethality in the Genus Nasonia“, authored by Brucker and Bordenstein from the Vanderbilt University. For this study, the researchers used three species of wasps of the Nasonia genus. Two of those species were genetically closely related while the third had diverged earlier in evolution. It appears their relative distance in the evolution tree also affected their relative proximity in the composition of their respective gut microbiota.
Hybrids of closely related species had a low rate of mortality (~8%), while those of distant species had a significantly higher mortality rate (>90%). Interestingly the microbiome of the survival hybrids were quite similar to that of their parents, whereas the microbiome of the hybrids that did not survive were completely different. The researchers then showed that the incompatibilities that caused the death of the hybrids had a microbial basis. The germ-free hybrids survived normally, but when given a gut microbiota from regular hybrids, their survival rate plummeted.
As stated by the authors in the abstract of their paper, the central element to remember here is that “in this animal complex, the gut microbiome and host genome represent a coadapted hologenome that breaks down during hybridization, promoting hybrid lethality and assisting speciation”. Thus evolution should be seen as a process which affects species together with their gut microbiota.