Caste-specific recognition patterns in a fungus-growing termite

Abstract

Discrimination between friends and foes is crucial for many superorganismal insects to ensure altruistic acts are only directed towards kin. However, whether or not an extremely sensitive recognition system is needed, could depend on the type of invaders that generally present a threat to the species in question. Ants are known to engage in intraspecific conflicts, and readily discriminate between nestmate and non-nestmate conspecifics. In contrast, fungus-growing termites do not invade or aggressively compete with neighbouring nests, but are instead often threatened by phylogenetically distant invaders, such as ants. Therefore, we hypothesized that termites have less need for a recognition system efficient in distinguishing small chemical differences. We studied intra- and interspecific recognition of the worker and soldier castes of the fungus-growing termite Macrotermes natalensis and investigated both recognition of and behaviour towards different stimuli of varying ecological importance. Both workers and soldiers were unable to efficiently discriminate against conspecific non-nestmates. Furthermore, we found that not only were soldiers more sensitive to small differences in chemical profiles than workers, but they also showed different behaviour than workers when a stimulus was recognized as foreign. Our results also raise the question whether termites have specifically evolved to recognize and react to the smell of ants. Our results reinforce the notion that nestmate recognition is a trait under stringent selection, where efficient recognition is only selected for when needed, probably because of the energetic costs of maintaining the neural tissue required. • Fungus-growing termites did not efficiently discriminate against non-nestmates. • Low intraspecific competition could lead to less selection pressure for gestalt odour. • Workers and soldiers differed in their sensitivity to stimuli and behaviour. • Ants elicited a specific response, likely due to termites being predated on by ants.