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In the 1960s, Penn biologist Dan Janzen, as part of earning his Ph.D., re-described what has become a classic example of biological mutualism: the obligate relationship between acacia-ants and ant-acacia trees. The acacia trees produce specialized structures to shelter and feed the ant colony, and the ants, in turn, defend the tree against herbivores.
In a new study in Proceedings of the National Academy of Sciences, colleagues of Janzen's in the Penn Biology Department uncover a genetic mechanism that programs the plant side of the ant-acacia relationship. Scott Poethig, a plant biologist, and Aaron Leichty, who earned his Ph.D. working under Poethig and is now a postdoctoral researcher at the University of California, Davis, showed that these species of acacia develop the traits necessary to feed the ant colony—hollow swollen thorns to house them, and nectaries and nutrient-rich leaflet tips called Beltian bodies to feed them—as part of an age-dependent phenomenon in plant development.
Cost - Traits - Poethig - Author - Report
"There is a cost associated with making these traits," says Poethig, senior author on the report, "but the plant needs them, otherwise it's a goner. Dan showed: no ants, no plants. The plant is eaten by everything from grasshoppers to mice.
"So there's a tradeoff happening. And what we found is that these traits seem to have evolved on the back of a preexisting pathway that governs a developmental transition in plants."
Adds - Leichty - Literature - Lot - Plant
Adds Leichty: "When we dug into the literature, we found that a lot of plant defense strategies are age-dependent. It's counterintuitive because you think the young plants would want to start making these structures right away so they wouldn't get eaten, but our findings as well as profound logic suggest there are biological constraints on making them."
Poethig has spent a large part of his career studying this transition, what some regard as a plant's "adolescence." But he hadn't...
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