Microbes can draw the line between species

Wasps' gut inhabitants can kill or save crossbreeds

Sometimes it takes guts, or rather microbes in the guts, to make a species.

SPECIES SAVER Parasitic jewel wasps (female shown injecting her egg into the pupa of a fly host) turn out to maintain their species barriers with help from microbes. Courtesy of Robert M. Brucker

Genes are, of course, important. But the live-in microorganisms of jewel wasps play such an important role in keeping species separate that changing gut microbes can also change whether cross-species offspring live or die, Vanderbilt University researchers report July 18 in Science.

The paper gives more details of Nasonia wasp experiments reported at the Evolution conference in Utah last month (SN Online: 7/2/13). In the study, authors Robert Brucker and Seth Bordenstein revisited the known problem of doomed male offspring from crosses between N. vitripennis and N. giraulti wasps. The scientists showed that gut microbes may play a crucial role in keeping the two species separate.

Biologists tracing how organisms separate into new species traditionally focus on genes, Brucker says. But an organism, be it a human or monkeyflower or wasp, actually lives as a community containing billions of microorganisms with their own genes and cells. The microbial community may be an overlooked force in shaping how an organism evolves, Brucker and Bordenstein propose.

Their experiments roused excitement at the meeting, but not everyone is willing to treat organism-plus-microorganism as a unit for evolution. Evolutionary biologist Jürgen Gadau of Arizona State University in Tempe also studies Nasonia species but considers the microbes as just an important part of the wasps’ environment.  

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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