Evolving away from sweets

Wednesday May 29, 2013

We’ve all heard the joke that cockroaches are so resilient and so hard to exterminate that they probably would survive a nuclear holocaust. The latest research suggests that humorous theory might not be too far off base.

In a study published last Thursday in the journal Science, researchers from North Carolina State University reported that some cockroaches have learned to reject the sweet-tasting corn syrup used to bait them into poisonous traps. In as little as five years, the sugar-rejecting trait had become so widespread that the bait had been rendered useless. The findings illustrate the evolutionary prowess that has helped make cockroaches so hard to stamp out.

The research focused on the German cockroach, a small kind that can hitch a ride into your home in a grocery bag. Typically, glucose excites neurons that tell the brain "Sweet!" But thanks to a genetic mutation in the German cockroaches, the glucose activates neurons that say "Sweet!" and ones that say "Yuck!" As the Associated Press reports, the "Yuck!" neurons dampen the signal from the others, so the brain gets the message the taste is awful.

The glucose aversion may have arisen in an individual cockroach in response to bait, according to Coby Schal, one of the authors of the study. Or it may have already been present in just a few individuals when the arrival of the bait suddenly gave them an advantage for surviving and reproducing. Their offspring would inherit the trait and increasingly replace other cockroaches.

Fortunately, tests show that the glucose-hating cockroaches are happy to eat most types of bait these days, suggesting that manufacturers have removed the glucose or masked it, Schal said. What’s more, the researchers found glucose-hating cockroaches in only seven of 19 populations they sampled from various locations.

Michael Scharf, an entomologist at Purdue University who studies urban pests but wasn’t involved in the new work, noted that since the 1950s, cockroaches have shown they can also evolve resistance to insecticides, the AP reports. He agreed the latest results should help scientists develop better products to control roaches.

That’s encouraging. After all, human should be smart enough to stay one evolutionary step ahead of those puny cockroaches, right? Then again, these particular cockroaches are smart enough avoid sugary treats that lead to premature death. We can’t always say the same about humans.


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