Love Is a Gut Feeling for Fruit Flies

Matchmakers: In Irish they are Babhdóir, in Yiddish they are Sadchen. For fruit flies, the matchmakers might be gut bugs.

Fruit flies (Drosophila melanogaster) with the same set of intestinal bacteria preferred mating with each other, discovered professors Eugene Rosenberg, Daniel Segel, and doctoral student Gil Sharon at Tel Aviv University in Israel. They published their results in the Proceedings of the National Academy of Science.

When the flies' intestinal bacteria were killed off with antibiotics, the flies mated randomly. When the bacteria were added back into their guts, they went back to mating preferentially.

Mating choice and reproductive separation are believed to drive evolution. And the researchers believe this study suggests evolution can be driven by a community of organisms living symbiotically, not just the individual organism. The symbiotic community of organisms, called a holobiont, evolves together. In this case, the fly's intestinal bacteria influenced mate choice.

In the experiment, the researchers mixed two different foods into the agar medium on which the fruit flies were raised. One lived on a standard cornmeal-molasses-yeast mixture. The other was raised on starch.

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The researchers observed that after three generations, the starch-fed flies had significantly higher quantities of the bacteria Lactobaccilus plantarum in their guts. The flies were then raised for one generation on the same food to eliminate the possibility that the smell or something else about the food itself could influence mating preference.

When they put four flies from these experimental groups, one virgin of each gender and food source, into the same enclosure, they found matchmaking commenced. Out of 38 matings, 29 were between those with the same bacteria in their guts. Starch-fed males mated with starch-fed females, and the cornmeal-mix-fed flies behaved likewise.

The researchers then raised another group of flies the same way, but killed the intestinal bacterial using antibiotics in the food media. When mixed together, these flies mated with each other freely. Starch-fed males mated with cornmeal-mix-fed females just as frequently as with starch-fed females.

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To test whether it was indeed the bacteria affecting the mating preference, another set of flies was treated with antibiotics to kill of any gut bacteria. They were then raised on media inoculated with bacteria taken from the CMY-media or starch-media. These flies then mated preferentially just as the first batch of flies had done, starch-fed with starch-fed and vice-versa.

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The researchers also observed a change in several chemicals the flies produced, called cuticular hydrocarbon sex pheromones. The chemical variation depended on the bacteria found in the flies' intestines. These chemicals help flies determine their mates. So the researchers hypothesize that the bacteria-influenced pheromone changes may cause the mating preferences.

PHOTO: Fruit flies mating; Wikimedia Commons