Task specialization influences nestmate recognition ability in ants
Insect societies are a paramount example of efficiency based upon division of labour. Social insect workers specialize on different tasks, such as brood care and foraging. This polyethism is underlined by the development of brain and olfactory organs. Nestmate recognition in ants is based on perception of chemical cues through olfaction; therefore, we asked whether task polyethism affects the ability of ants to discriminate friends from foes. We used the carpenter ant Camponotus aethiops to investigate the ability of three behavioural groups of worker (foragers, nurses and inactives) in recognizing intruders. Foragers, which are older workers mainly performing tasks outside the nest, showed higher levels of aggression towards intruders than nurses did. Foragers appeared to be more efficient at recognizing non-nestmate cues than did intra-nidal workers (nurses and inactives), and they possibly have higher motivation to attack. This suggests that ant workers change their olfactory sensitivity to non-nestmate stimuli during their life. This plasticity could be adaptive, as younger workers, who typically stay inside the nest, usually do not encounter intruders, while older workers have more experience outside the nest and differently developed neural circuits. A sensitive nestmate recognition system would thus be an unnecessary cost early in life.
Ants are known to divide their workforce, often as a product of age. Younger workers take on safer tasks such as taking care of the brood, while older workers are often involved with more dangerous tasks such as foraging and defending the nest. Here, we show that workers change their olfactory sensitivity to intruders during their life. As a result, foragers are better than nurses at detecting intruders. Furthermore, foragers appeared to not only be more sensitive but also have higher motivation to attack. The higher sensitivity of foragers is most likely adaptive, as younger workers stay in the nest and typically do not encounter intruders, and a sensitive recognition system would be for them an unnecessary cost.
KeywordsPolyethism Olfactory sensitivity Nestmate recognition
Thanks to the members of the Centre for Social Evolution (CSE), University of Copenhagen for the pleasant working environment, in particular David Nash for providing useful comments. This study was supported by The Danish National Research Foundation (CSE), a Freia grant from the Faculty of Science, University of Copenhagen and a Marie Curie Reintegration Grant, both assigned to PdE, and the German Academic Exchange Service (DAAD), supporting VN. NB was supported by the Academy of Finland (decision numbers: 251337, 252411 and 289731) and the University of Helsinki.
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