Hidden aggression in termite workers: plastic defensive behaviour dependent upon social context

Abstract

SummarySocial insect colonies are self-organized systems that respond to changes in environmental conditions by altering the relative proportions of certain castes or individuals engaged in specific tasks.While termites are known to regulate the ratio of morphologically specialized soldiers in response to the proportion of nestmate castes, soldier-differentiation process requires a relatively long time to be accomplished. Consequently, other plastic and flexible mechanisms are considered to be employed as one of the various defensive strategies in termites. In this study, the defensive behaviours of soldiers, pseudergates (workers) and reproductives of the damp-wood termite Hodotermopsis sjostedti were quantified. When individuals of the caste were exposed to an intruder, soldiers exhibited the most vigorous defensive behaviour, followed by pseudergates and then reproductives.While the aggression levels of soldiers and reproductives were independent of the accompanying castes, pseudergate aggression was more plastic and depended on the other castes present. When paired with reproductives, pseudergates exhibited high levels of aggression toward enemies. However, pseudergate aggression levels remained low when they were paired with soldiers, suggesting that pseudergates moderated their defensive behaviour depending on social context. Plasticity with respect to social behaviours may facilitate rapid and 3 flexible responses required for colony defence.

Communication and Social Regulation in Termites

“…Instantaneous levels of aggression are also fine-tuned based on the actual caste composition of the colony at the site of the conflict. Zootermopsis pseudergates are more aggressive towards intruders when they are close to reproductives or when only a few soldiers are around (Ishikawa and Miura 2012). When there is a high proportion of nymphs in a colony, the level of agonism may be decreased, which facilitates the colony's acceptance of and potential fusion with a conspecific colony that has a lower proportion of nymphs.…”

Behavioural plasticity of social trematodes depends upon social context

“…Socially mediated behavioural plasticity in trematodes is analogous to the adjustable aggression levels of termite workers towards intruders depending on the presence of nest-mate soldiers [4]. Although the two taxa are distantly related, they share a suite of ecological features that may have led to a convergence of their social organization and behaviour.…”

“…Although division of labour through formation of physical castes occurs in diverse organisms (insects [3], snapping shrimps [6], sea anemones [7], mole rats [8], parasitic trematodes [9,10]), behavioural plasticity of individual caste members depending upon social context has only been documented in insects [4,5]. In the recently discovered social trematodes, we investigate whether the reproductive morphs of Philophthalmus sp.…”

“…Such plasticity can be manifested in relation to the density of other colony members; indeed, some social insects show plasticity in morphologies and behaviours in response to changing caste ratios [3]. For example, termite workers demonstrate increased aggression towards intruders when soldiers are removed from the colony [4,5].…”

“…Behavioural plasticity allows colonies to sustain ergonomic efficiency of the whole without paying the cost of producing additional individuals [4]. Such plasticity can be manifested in relation to the density of other colony members; indeed, some social insects show plasticity in morphologies and behaviours in response to changing caste ratios [3].…”