The role of personality and experience in bimodal signal integration in a territorial poison frog

Multimodal communication, in which multiple signal modalities are combined to produce a single compound signal, is employed by many species and can mediate a wide range of fitness-relevant behaviours. While the form and function of multimodal signals have been extensively studied, we know little about how individual traits such as personality and experience influence receivers' responses to these signals. We investigated how aggressiveness and experience affect the behavioural responses to bimodal signals in the brilliant-thighed poison frog Allobates femoralis. In this species, male advertisement calls constitute a fixed bimodal signal, as the production of sound is coupled with the inflation of the vocal sac, which adds a visual cue. We presented territorial males with a synthetic advertisement call (acoustic cue) and a model frog with a pulsating vocal sac (visual cue), and manipulated signal ambiguity by varying the spatial distance between the two components. We predicted personality and experience would affect how males responded to the bimodal signal depending on its level of ambiguity, and expected younger and/or more aggressive males to respond faster and to attack the visual cue more frequently than older or less aggressive males, especially under high signal ambiguity. Contrary to our predictions, neither aggressiveness nor experience influenced response latency or attack likelihood. Instead, all males displayed a consistent population-level pattern: as the spatial separation between the visual and acoustic signal components increased, they were less likely to attack the model, and their initial and overall interactions shifted from the visual model to the sound source. These findings suggest that the fixed bimodal signals in A. femoralis selected for robust and uniform receiver responses to maintain reliable communication during high-stakes social interactions such as territorial defence. Aggressive receiver responses seem to be dual-staged, consisting of far-field phonotaxis to the acoustic signal component and visual and multimodal signals only becoming relevant during near-field aggression. Future studies should compare how ecological and social factors shape receivers' responses across species with varying degrees of coupling between the signal components in order to better understand the evolution of multimodal signalling and of the diversity of receiver strategies.