Cheating ants smell funny....

Aphaenogaster cockerelli, Arizona

Here's a new study in Current Biology from Adrian Smith, Bert Hoelldobler, and Juergen Liebig:

Abstract: Cheaters are a threat to every society and therefore societies have established rules to punish these individuals in order to stabilize their social system [1â3]. Recent models and observations suggest that enforcement of reproductive altruism (policing) in hymenopteran insect societies is a major force in maintaining high levels of cooperation [4â6]. In order to be able to enforce altruism, reproductive cheaters need to be reliably identified. Strong correlational evidence indicates that cuticular hydrocarbons are the means of identifying cheaters [7â14], but direct proof is still missing. In the ant Aphaenogaster cockerelli, we mimicked reproductive cheaters by applying a synthetic compound typical of fertile individuals on nonreproductive workers. This treatment induced nestmate aggression in colonies where a queen was present. As expected, it failed to do so in colonies without a queen where workers had begun to reproduce. This provides the first direct evidence that cuticular hydrocarbons are the informational basis of policing behaviors, serving a major function in the regulation of reproduction in social insects. We suggest that even though cheaters would gain from suppressing these profiles, they are prevented from doing so through the mechanisms of hydrocarbon biosynthesis and its relation to reproductive physiology. Cheaters are identified through information that is inherently reliable.

In less technical language, fertile ants smell different than infertile ants, and when researchers painted the fertility odor on non-reproducing workers, in colonies that already had active queens, the hapless ant was attacked by her sisters.  So colonies have a way to maintain social order that does not rest entirely on the altruism of individuals to forgo reproduction.  They, like us, have police.

Of course, we already knew that ants, bees, and wasps engage in this sort of policing.  What is novel in the Smith et al study is an experimental test of how the worker police recognize the cheaters.  As in much of ant communication, the cue is chemical.

source: Smith, A. A., Hoelldobler, B., Liebig, J. 2009. Cuticular Hydrocarbons Reliably Identify Cheaters and Allow Enforcement of Altruism in a Social Insect. Current Biology 19: 78-81. doi: 10.1016/j.cub.2008.11.059.