Gut Microbiome Splits a Species

sn-wasp

Jewel wasps lay their eggs (light blue) inside the pupas (brown) of certain flies. The wasp larvae (orange) feed on the fly, pupate, and then chew their way out as adults. Credit: Robert M. Brucker.

This is some fascinating research, published in the latest issue of the journal Science. Ed Yong has a great writeup about it, but unfortunately the original paper is behind a paywall. It demonstrates that a species split can happen not merely because of incompatible DNA, but because gut bacteria inside the two species is different.

✤ The work involved three different species of parasitic jewel wasps. Two of the species, Nasonia giraulti and N. longicornis, are closely related, whereas the third species, N. vitripennis, diverged from the other two about 1 million years ago.

N. giraulti and N. longicornis are able to mate in the lab, producing viable offspring; but when either mates with N. vitripennis, almost all male larvae in the second generation die.

✤ Typically, it is incompatible DNA that prevents the generation of viable offspring from a mating. Researchers at Vanderbilt University questioned if the reason for this mortality went beyond incompatible DNA. Previous work had shown that the gut microbes in N. vitripennis was different from the other two species, and they wondered if these microbes could be the reason the offspring died.

✤ In an elegant experiment, they raised all three species of Nasonia without gut microbes, by feeding them sterile food from birth. They found that almost all of the second generation offspring from matings between N. vitripennis and N. giraulti wasps survived.

✤ Next, to confirm their suspicions, they reintroduced bacteria into the bacteria-free wasps and most of the second generation offspring died. As a possible mechanism for this phenomenon, it could be that some parental genes aid the immune system to keep incompatible gut bacteria in check, and without these parental genes the gut bacteria can kill the offspring.

✤ It appears that in this complex system, the gut microbiome and the wasp genome represent a co-adapted ‘hologenome’ that helps assist in the formation of new species.

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