A classic example of a mutualism, or a mutually beneficial relationship between two species, is that of warm-climate Acacia plants and their ant tenants. The plants provide the ants with shelter within their hollowed-out thorns and food in the form of nectar and protein. The ants, in return, defend the tree viciously, attacking anything that comes near – from other insects to birds and small mammals.
One species of bug, however, has exploited this system. These insects, in the family Coreidae, roam freely on one species of Acacia and feed on the plants' leaf tissue. Susan Whitehead of the University of Colorado wanted to know just what makes these bugs seemingly invisible to the watchdog ants.
Whitehead hypothesized that the bugs might be acting in some way that the ants found acceptable. Since ants use pheromones to communicate with one another, she also wondered if the bugs were mimicking the scent of the ants. When she and her colleagues immobilized the bugs, the ants still did not attack them. But when the researchers washed the bugs in a chemical solvent and returned them to the plants, the ants immediately swarmed the bugs.
The key, says Whitehead, was the removal of chemicals on the bugs' exoskeleton. Using chromatography and spectrometry, the researchers compared the bugs' exoskeletal chemicals with that of the ants.
"The chemicals in the bugs' cuticle matched that of the ants," says Whitehead. "The bugs mimic the hydrocarbons that the ants produce, so the ants don't recognize them as something foreign."
Even if this chemical camouflage is energetically costly for the bugs to produce, the benefits outweigh the costs, says Whitehead.
"Here, the bugs have tapped into a resource in a competition-free space," she says. "It emphasizes that even the most classic examples of mutualism in nature are not infallible."
Animals and plants communicate with one another in a variety of ways: behavior, body patterns, and even chemistry. In a series of talks at the Ecological Society of America's annual meeting, to be held August 3-7 in Albuquerque, New Mexico, ecologists explore the myriad adaptations for exchanging information among living things.
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