Royal presence promotes worker and soldier aggression against non-nestmates in termites

Abstract

Many eusocial insects can distinguish nestmates from non-nestmate conspecifics, which ensures that altruistic behavior is directed toward close relatives. In termites, however, colonies exhibit various responses to non-nestmates: from killing to accepting as a colony member. Why and how termite colonies adopt closed versus open societies remain largely unknown, while it is presumably related to not only genetic but also social-environmental factors. Here, we show that kings and queens play a key role in maintaining high aggression levels of workers and soldiers toward non-nestmate intruders in the subterranean termite Reticulitermes speratus. The level of aggression toward non-nestmate conspecifics was significantly lower in “royal-absent” colonies compared to “royal-present” colonies. In addition, the proportion of workers and soldiers exhibiting aggressive behaviors toward non-nestmates decreased in the absence of kings and queens. Our results demonstrate that social conditions, including royal presence, can influence intercolonial interactions, and may explain why previous studies of termite aggression have reported contradictory findings. This study provides important new insights into nestmate recognition and colony defense in eusocial insects.