Spectral sensitivity, spatial resolution and temporal resolution and their implications for conspecific signalling in cleaner shrimp

Cleaner shrimp (Decapoda) regularly interact with conspecifics and client reef fish, both of which appear colourful and finely patterned to human observers. However, whether cleaner shrimp can perceive the colour patterns of conspecifics and clients is unknown, because cleaner shrimp visual capabilities are unstudied. We quantified spectral sensitivity and temporal resolution using electroretinography (ERG), and spatial resolution using both morphological (inter-ommatidial angle) and behavioural (optomotor) methods in three cleaner shrimp species: Lysmata amboinensis, Ancylomenes pedersoni and Urocaridella antonbruunii. In all three species, we found strong evidence for only a single spectral sensitivity peak of (mean +/- s.e.m.) 518 +/- 5, 518 +/- 2 and 533 +/- 3 nm, respectively. Temporal resolution in dark-adapted eyes was 39 +/- 1.3, 36 +/- 0.6 and 34 +/- 1.3 Hz. Spatial resolution was 9.9 +/- 0.3, 8.3 +/- 0.1 and 11 +/- 0.5 deg, respectively, which is low compared with other compound eyes of similar size. Assuming monochromacy, we present approximations of cleaner shrimp perception of both conspecifics and clients, and show that cleaner shrimp visual capabilities are sufficient to detect the outlines of large stimuli, but not to detect the colour patterns of conspecifics or clients, even over short distances. Thus, conspecific viewers have probably not played a role in the evolution of cleaner shrimp appearance; rather, further studies should investigate whether cleaner shrimp colour patterns have evolved to be viewed by client reef fish, many of which possess triand tetra-chromatic colour vision and relatively high spatial acuity.