Meeting Abstract

67-1   10:30 - 10:45  Signal boost: nanoparticles enhance antennal reflectance in the cleaner shrimps Ancylomenes pedersoni and Lysmata amboinensis Davis, AL*; Caves, E; Johnsen, S; Duke University; University of California, Santa Barbara; Duke University alexander96davis@gmail.com

Cleaner shrimps engage in a mutualistic interaction with reef fishes ‘clients,’ in which they remove ectoparasites and dead skin from clients. In several species of cleaner shrimps, it has been shown that these cleaning interactions are mediated by visual signals, and thus may be a valuable system for studying interspecific signaling. Two species, Ancylomenes pedersoni and Lysmata amboinensis have been shown to signal to clients using white body parts, including antennae. The antennae are thin (< 150 ?m), but they remain remarkably bright at depth and seem to serve as effective signals even to reef fish with relatively low acuity. We predicted that selection for signal salience may have led to the evolution of micro- or nanostructures that increase reflectance in antennal signaling structures. Using spectrophotometry, we found that the antennae reflect 40-65% of light in these two species. Scanning electron microscopy revealed that the antennae of both species contain a 1-3 ?m thick layer of densely packed nanoparticles between 300-400nm in diameter. After identifying the nanoparticle layer in both species, we used finite-difference time-domain simulations to quantify how changes in the size of the particles, thickness of the particle layer, and refractive index of the particles affect reflectance. Our modeling demonstrates that while the layers are far less thick than those that produce maximum reflectance, the particles are well sized and likely have a high enough refractive index to significantly increase reflectance. Together, our modeling suggests that the nanoparticle layer is effective in enhancing the brightness of the antennae. Future work should examine how the intensity of antennal reflectance affects signaling interactions with client fish.