ECOLOGY: Sucrose-Free Sips Suit Acacia Ants -- Pennisi 308 (5721): 481a -- Science:
The thorny acacia tree has strong allies: vicious, centimeter-long ants whose nasty bite scares off plant-eating animals and also humans. In return for defending acacias, the ants get free meals and places to live. The key to this sweet deal is the sucrose-free nectar provided by the plant, says Martin Heil, an ecologist at the Max Planck Institute for Chemical Ecology in Jena, Germany. As he and his colleagues report on page 560, a sucrose-degrading enzyme produced by the acacia customizes its nectar to appeal to the right ant partners. The defensive-minded ants that protect the tree prefer their nectar without sucrose, while other ants do not, the researchers found.
Furthermore, the acacia ants have actually decreased their own production of the same sucrose-degrading enzyme, reinforcing this particular pairing of insect with plant. The work "gives one of the first examples of a biochemical basis for behavior difference in plant-insect mutualisms," says Robert Thornburg, a biochemist at Iowa State University in Ames. "It shows that coevolutionary trends can be underlain by biochemistry."
Co-evolution at work.