Hidden aggression in termite workers: plastic defensive behaviour dependent upon social context
Highlights
► We quantified the defensive behaviour of soldiers, reproductives and workers in a termite species. ► Only workers showed behavioural plasticity among the castes. ► Workers showed less aggression when accompanied by soldiers. ► They showed high aggression when accompanied by reproductives. ► Social context affects workers’ behaviour resulting in flexible colony defence.
Section snippets
Insects
Colonies of H. sjostedti were sampled from decaying wood in evergreen forests on Yakushima Island in Kagoshima Prefecture, Japan. Colonies were maintained in the laboratory as stock at approximately 25 °C under constant darkness. Soldiers, neotenics and pseudergates were used for the behavioural experiments. As in previous studies (Miura et al., 2000, Miura et al., 2004), seventh-instar larvae were regarded as pseudergates in this study. This species is considered to have two reproductive
Responses towards Intruders when Isolated
As in nature, under isolated conditions, soldiers exhibited defensive behaviours more frequently than the other castes (Fig. 2, Table 2). After encountering an ant, the soldiers bit it repeatedly until it was dead; the frequency of this defensive behaviour then decreased. Soldiers rarely exhibited an escape response after encountering an ant. Pseudergates also exhibited several defensive behaviours under isolated conditions (Fig. 2). Upon encountering an ant, pseudergates often bit the ant
Discussion
Our results showed that pseudergates possess the potential to attack enemies by altering their behaviour in a context-dependent manner. When exposed to an intruding ant, pseudergates exhibited relatively low levels of aggression in the presence of soldiers, but very high levels of aggression in the presence of neotenics (Figure 3, Figure 5). A similar result was observed in the manner in which pseudergates located themselves within the nest in response to a nest disturbance (Figure 4, Figure 5
Acknowledgments
We are grateful to K. Maeno, Y. Hayashi, M. K. Hojo, A. Ishikawa and K. Ogawa for their valuable comments on this study. We thank W. M. Iwasaki, A. S. Tanabe and M. P. Sato for their support in the statistical analysis. We also thank Y. Hayashi, M. K. Hojo, T. Yodoi and K. Tanabe for their assistance in field sampling and laboratory experiments. This work was supported by a Grant-in-Aid for Young Scientists (No. 21677001) from the Ministry of Education, Culture, Sports, Science and Technology
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Present address: Graduate School of Life Sciences, Tohoku University, Sendai, Japan.