Reciprocal signals mediate cleaning interactions between cleaner shrimp and their reef fish clients

Abstract

Signaling between a sender and a receiver mediates many behavioral interactions. In reciprocal signaling systems, both partners can send and receive signals, raising questions about the circumstances under which each party signals, and whether and how an interaction’s outcome is impacted by the signaling behavior of each party. In marine cleaning mutualisms, cleaner shrimp or fish consume ectoparasites and dead skin from larger ‘client’ fish partners. Cleaners signal their intent to clean to clients, and clients often signal their intention to be cleaned by changing color. Here, we used in situ observations of cleaner-client interactions to investigate signal-mediated cleaning interactions between the cleaner shrimp Ancyclomenes longicarpus and its client fish partners. We asked if client characteristics (size, status as a predator) influence signaling behaviors in both partners, and explored how signals and client identity (i.e. predatory status) impact the outcome of cleaning interactions. Our findings showed that larger client species were more likely to both signal and be signaled to. Additionally, interactions involving signals from either partner were more likely to result in cleaning than those that did not involve signals, and cleaning tended to last longer when only clients signaled or when clients were predatory species. Our results suggest that signals from both parties are key factors determining whether cleaning occurs, while client signaling and predatory status influence cleaning duration. Overall, we highlight the complex ways in which assessment of mutualistic partners via reciprocal signaling is both influenced by partner identity and affects the interaction’s outcome.