Variation in stomatopod (Gonodactylus smithii) color signal design associated with organismal condition and depth

In interactions, many tropical stomatopod species display conspicuous colored body spots that can communicate information about the sender's state (e.g., sex, aggressiveness, etc.). Species inhabiting a variety of depths experience large differences in illumination spectrum and intensity due to filtering of light by water and its constituents. Stomatopod spectral sensitivity is known to vary phenotypically with changes in light environment (associated with depth) that potentially affects the detection of color signals. Animals collected at different depths also have different body coloration. This study examines how spectral differences in colored body spots vary with organismal condition and models the effects of changing body coloration, light environment, and spectral sensitivity on the detection of color signals in a gonodactyloid species, Gonodactylus smithii. Of the seven conspicuous color spots that were measured in G. smithii, three had spectral differences that correlated with sex, aggression, and female reproductive state. A model of color detection in G. smithii indicates that longer-wavelength spectral content was affected most by varying body coloration and light conditions. Most color signals were perceived similarly both by shallow- and by deep-adapted photoreceptor sets over a range of depths (1-13 m). Eye spot ('meral spot') color detection also was invariant over the same depth range in shallow- and deep-adapted, long-wavelength receptors, but deep-adapted receptors continued to maintain a consistent detection of these spots down to 18 meters. These results suggest that meral spot coloration may have evolved as a constant signal when viewed by conspecifics from various depths.