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Ants that can rest on their pants

Shrewd investments in the slave trade

Munich, 11/25/2011

Protomognathus americanus has got it all “worked” out. This ant, just 3 mm long, lives in colonies made up of only a few conspecifics.  Often, a whole colony fits in a hollow acorn. There’s not all that much housework to do, one might think. Nevertheless, these ants raid the nests of a different ant species and carry off their young pupae, which they then keep as slaves, forcing them to work in their own colonies. By the time they mature, the prisoners have taken on the characteristic scent of their new surroundings and feel at home. Biologist Sebastian Pohl, a doctoral student in the Department of Biology II at LMU Munich, has shown that P. americanus, a North American species, is able to gauge the needs of its own colony before setting out on a raid. “Although each colony contains less than ten workers, raiding parties never consist of more than a few of them. The rest remain in the nest,” he says. “However, the precise division of labor varies, depending on how many new slaves are required.” The solitary scouts that locate possible targets are infertile, but half of the workers in the nest were found to be fertile. This division of labor is reflected in their chemical profiles, which convey information about their function and status to nestmates. Colonies of P. americanus depend completely on their slaves to feed them, and must therefore mount raids periodically. This is a risky business, because they tend to choose particularly large nests as targets – despite the fact that the loss of even a few scouts would put their own colony at risk. However, Pohl and his colleagues have previously demonstrated that this high-risk strategy is likely to pay off. Big nests promise big rewards, and a single successful raid can ensure that the bosses can then put all six feet up for a long time. (suwe/PH)

Division of labor and slave raid initiation in slave-making ants
Sebastian Pohl, Volker Witte, Susanne Foitzik
Behavioral Ecology and Sociobiology, Vol. 65, No. 11, November 2011
doi: 10.1007/s00265-011-1212-4

Slave-making ants prefer larger, better defended host colonies
Sebastian Pohl, Susanne Foitzik
Animal Behaviour, Vol. 81, No. 1, January 2011

Sebastian Pohl
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