Seeing double: visual physiology of double-retina eye ontogeny in stomatopod crustaceans.

Stomatopod eye development is unusual among crustaceans. Just prior to metamorphosis, an adult retina and associated neuro-processing structures emerge adjacent to the existing material in the larval compound eye. Depending on the species, the duration of this double-retina eye can range from a few hours to several days. Although this developmental process occurs in all stomatopod species observed to date, the retinal physiology and extent to which each retina contributes to the animal's visual sensitivity during this transition phase is unknown. We investigated the visual physiology of stomatopod double retinas using microspectrophotometry and electroretinogram recordings from different developmental stages of the Western Atlantic species Squilla empusa. Though microspectrophotometry data were inconclusive, we found robust ERG responses in both larval and adult retinas at all sampled time points indicating that the adult retina responds to light from the very onset of its emergence. We also found evidence of an increase in the response dynamics with ontogeny as well as an increase in sensitivity of retinal tissue during the double-retina phase relative to single retinas. These data provide an initial investigation into the ontogeny of vision during stomatopod double-retina eye development.