Vision and signaling behavior in cleaner shrimp-client fish mutualisms

Eleanor Caves

University of California, Santa Barbara

Department of Ecology, Evolution, and  Marine Biology

Cleaner shrimp are small tropical crustaceans that clean their reef fish clients by removing ectoparasites. Although many client species eat crustaceans, cleaner shrimp are rarely eaten during cleaning interactions. In this talk, I discuss evidence supporting the hypothesis that cooperation between cleaners and clients is mediated by visual signals. I first discuss the visual capabilities of each party, and then apply those measures of visual capability to in situ interactions between cleaner shrimp and client fish in two cleaner species—the Caribbean Ancylomenes pedersoni and the Indo-Pacific Lysmata amboinensis—to examine how they may appear to their mutualistic partners. Network analysis approaches show that certain cleaner and client behaviors function as visual signals. In A. pedersoni, we found that signaling by both parties, but primarily the cleaner, is necessary to initiate cleaning. In L. amboinensis, we found that cleaners adjust their signaling and cleaning behaviors when interacting with predatory versus non-predatory clients, in a way that minimizes potential risks. Despite being in different families and living in distinct parts of the globe, both species possess conspicuous white antennae that play a role in signaling. In both species, the antennae broadly reflect 40-65% of light, and scanning electron microscopy revealed the antennae have a layer of densely packed nanoparticles 300-400nm in diameter, which likely have a high refractive index. Optical modeling showed that the nanoparticle layers are well sized to increase reflectance, enhancing the brightness of these important signaling structures. I briefly touch on future work on this system, which is poised to become a model for studies of the evolution and dynamics of interspecific signaling.