HOUSTON -- (Feb. 21, 2011) -- Texas winters may seem mild to those who move here from farther north, but they can be hard to adjust to for immigrants from warmer climates. This is true not only for people but for ants too. A new study by biologists at Rice University and the University of Texas at Austin (UT) finds that the Texas leaf-cutter ant Atta texana, whose ancestors emigrated from the tropics, adapted to the relatively harsh Texas winters in an unusual way -- through their food.
Like all leaf-cutter ants, A. texana cuts leaves but does not eat them.
"Leaf-cutters can't digest the nutrients of leaves directly, so they use a fungus called Attamyces as a kind of external digestive system," said co-author Scott Solomon, a lecturer in ecology and evolutionary biology at Rice. "It's an example of a relationship that biologists call mutualism. The ants are completely reliant on the fungus, and the fungus -- which only occurs in leaf-cutter colonies -- is likewise reliant on the ants."
The new study, which appears this week in the Proceedings of the National Academy of Sciences, found that leaf-cutter colonies in northern Texas and Louisiana, where winter temperatures regularly get below freezing, have found new ways to cope with the cold. Most leaf-cutter ant species are native to the predictably warm tropics, so the Attamyces fungus has adapted to a narrow range of temperatures. Previous studies have found the ants are attentive gardeners; they keep an ever-present watch on their subterranean gardens, and they are careful to regulate humidity in the gardens and to weed out anything that threatens the crop.
Solomon began studying leaf-cutter ants as a graduate student in the UT-Austin laboratory of lead co-author Ulrich Mueller. Solomon continued investigating leaf-cutter ants and their close relatives while he was based in Brazil and Washington, D.C., during a postdoctoral fellowship from the National Science Found
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