Physiological and behavioral evidence for multiple spectral channels in the larval stomatopod visual system

Larval stomatopods have generally been described as having a typical larval crustacean compound eye, which lacks the visual pigment diversity and morphological specializations of the well-studied stomatopod adult eye. However, recent work has suggested that larval stomatopod eyes are more complex than previously described. In this study, we provide physiological and behavioral evidence of at least three distinct photoreceptor classes in three species of larval stomatopods: Gonodactylellus n. sp., Gonodactylaceus falcatus and Pullosquilla n. sp. First, electroretinogram recordings were used to measure the spectral sensitivity of each species. Evidence for at least three spectral classes were identified in each: an ultraviolet, peaking at 340-376 nm; a short-wavelength blue, peaking at 455-464 nm; and a long-wavelength orange, peaking at 576-602 nm. Next, the behavioral response to light was investigated. We found that each species demonstrated positive phototactic responses to monochromatic stimuli across the UV-visible spectrum. In wavelength preference trials, distinct preferences among species were identified when different colored light stimuli were presented simultaneously. All species displayed a strong response to the UV stimulus, as well as responses to blue and orange stimuli, although at different response strengths, but no response to green. The results of this study demonstrate that larval stomatopods not only have multiple physiologically active spectral classes but they also display clear and distinct responses to wavelengths across the spectrum. We propose that the spectral classes demonstrated in each are related to visually guided ecological tasks of the larvae, which may differ between species.