Ant cheats plant; plant cheats back

A tropical tree acts as a fickle but pragmatic landlord, report researchers in Brazil.

INVITATION DROPPED. Young leaves of an Amazonian tree grow pairs of pockets at their base, perfect for ant shelters. As the tree matures and opens vulnerable blooms, leaves lose their pockets. Oecologia

This small tree of the central Amazon, Hirtella myrmecophila, grows a pair of little pouches at the base of young leaves. Two-millimeter-long ants of the species Allomerus octoarticulatus move into the pouches.

Plenty of plants offer ants special shelters in exchange for protection from other insects, says Heraldo L. Vasconcelos of Universidade Federal de Uberlndia in Brazil. Sometimes, however, ants exploit the trees’ good will by not doing their part. In the case of H. myrmecophila, the trees take an unusual countermeasure, report Vasconcelos and Thiago J. Izzo of the Instituto Nacional de Pesquisas da Amaznia in Manaus, Brazil. In a preserve north of Manaus, they found that as leaves age, they shed their little ant pockets.

To figure out why, the researchers excluded ants from some branches. Those branches lost about half their new growth to pests. But the antfree branches also kept about eight times as many flowers as ant-laden counterparts did. In the October Oecologia, the researchers propose that the tree benefits from ant security guards when foliage is young but then drops its cozy pouches from branches of mature leaves, preventing the ants from damaging too many flowers.


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Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.