Comment le cafard a déjoué les pièges au glucose…
Scientists uncover a secret to cockroaches’ adaptability - latimes.com
▻http://www.latimes.com/news/science/la-sci-cockroaches-sugar-20130524,0,4273705.story
Now researchers have discovered how some roaches have eluded humans’ once-infallible traps: They have evolved so that glucose-sweetened bait tastes bitter.
The discovery, published in Friday’s edition of the journal Science, solves a 20-year mystery and sheds light on the cockroach’s powerful ability to adapt.
“These roaches are unbelievable,” said Walter Leal, a chemical ecologist at UC Davis who was not involved in the study. “There’s an arms race here.”
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Silverman revisited the question two decades later, after he had joined the faculty of North Carolina State University in Raleigh. Using a network of cockroach collectors around the world who picked up samples from infested homes on the U.S. mainland and in Puerto Rico and Russia, he and his colleagues gathered 19 different populations of German cockroaches and tested the bugs for the anti-sweet-tooth.
This was easy enough: Normal cockroaches will gladly dig into a batch of sweet, sticky jelly, while glucose-averse roaches will jump back, as if repulsed.
Sure enough, the glucose-haters cropped up in seven of the populations studied, said Coby Schal, an entomologist at North Carolina State and senior author of the Science study.
“It’s really interesting how they jump away from it,” he said. “It’s like an electric shock almost.”
The cockroach’s taste system is much more decentralized than that of humans, Schal said. They have taste buds on several facial appendages, and even on their feet.
The researchers focused on the paraglossae, which sit closest to the cockroach mouth and allow the critters to taste objects before eating them. The paraglossae are lined with hairlike sensilla, just a few micrometers long, that contain taste receptor neurons.
The researchers stuck tiny glass electrodes onto these sensilla and then had the cockroaches taste a variety of sweet and bitter compounds, including fructose (the sugar found in fruit) and caffeine (whose bitterness is used by plants to deter predators). Then they watched the electrical signals the neurons sent to the brain. Signals for “sweet” had a very different shape than those for “bitter,” Schal said. That gave the scientists a fingerprint of each taste.
Next they fed the cockroaches a glucose-laced solution and watched the electrical signals. For normal cockroaches, glucose triggered a “sweet” signal. But in the glucose-averse cockroaches, the solution triggered both “sweet” and “bitter” signals.
Mystery solved: The warning was coming straight from the tips of their taste bud