Social insect sisters smell alike

December 29, 2010
This press release is also available in Danish ( Dansk).

In social insect colonies, workers generally cooperate within extended families consisting of full- and half-sisters. It has been suggested that they do not behave nepotistically, i.e. prefer to cooperate with full-sisters only, because they are not able to distinguish between half- and full sisters Actually, some ant species might know better, as researchers from Denmark, France, and the UK now found out.

Social insect societies are generally seen as nature’s finest example for cooperation. To help their mother queen, workers forego producing own offspring to increase the number of siblings their mother can rear, some of which will become new queens. In this way, the workers pass on their genes through siblings instead of offspring. Researchers therefore believe that high relatedness among colony members was important in the evolution of social insect colonies.

In some social insect species, the queens mate with more than one male, and hence not all of the workers are full sisters. Instead, several genetic lineages exist inside a single colony, with workers being full sisters within, but only half sisters between the lineages. Each worker would have a better chance of passing on its genes if it could preferentially help full-sisters rather than half-sisters, but the colony as a whole would be less efficient as a result of these internal power struggles.

Previously it has been thought that workers were not able to act nepotistically because they had no information that would allow them to discriminate between full- and half-sisters. By obscuring genetically based recognition cues, the colony would be safe from harmful struggles between worker lineages. Now, researchers from the Centre for Social Evolution (Universitiy of Copenhagen), and the Universities of Leeds and Paris 13, analysed both the odours of leaf-cutting ant workers and their genetic relatedness. They found that chemicals on the ants’ bodies are specific to the different genetic full-sister lineages within colonies. These chemicals, cuticular hydrocarbons, make up odours that were already known to be used for recognition by ants in other contexts, such as defending their nest from enemies. It is therefore likely that an ant can smell the difference between a full and a half sister, and in principle also use this information to preferentially help full sisters. This result demonstrates how much potential for conflict there is even in those insect societies that are seemingly governed by harmonious cooperation.

 Nehring,V., Evison, S.E.F, Santorelli, L.A., d’Ettorre, P. & Hughes, W.O.H: Kin-informative recognition cues in ants. Proceedings of the Royal Society B, online early 1.12.2010

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