D3362: Does disturbance stridulation in the passalid beetle Odontotaenius disjunctus function as a form of social communication?

Stridulation is the rubbing of body parts together to generate sound. Across class Insecta, stridulation functions as an important component of many essential behaviors including courtship, social recruitment, and predator deterrence. The subsocial passalid beetle Odontotaenius disjunctus boasts the largest acoustic repertoire of any beetle and performs a distinct stridulation when disturbed by predators. Previous studies have shown support for the hypothesis that this stereotyped disturbance stridulation has a deterrent effect on predators, lengthening handling time and thus improving probability of escape. We investigated whether disturbance stridulation also functions as a form of social communication. Because these beetles live in small social groups with high relatedness, we hypothesized that disturbance stridulation may signal retreat or rescue behaviors among kin, either of which have the potential to benefit inclusive fitness during a predation event. To test this, we placed beetles from the same social group in a test arena and exposed them to disturbance stridulations, observing whether each beetle moved away-from or towards the source of the sound. We also used an established ethogram to estimate behavioral diversity before and after exposure to disturbance stridulation, which, according to information theory, is predicted to increase when communication has occurred. Lastly, we compared changes in specific behaviors in the ethogram that are associated with aggression or retreat. These results extend our understanding of the various adaptive values of stridulation across species and contexts.