The Visual Ecology of Stomatopod Larvae

Despite researchers' interest in adult stomatopod vision, only a handful of studies have investigated stomatopod larval visual ecology, the function of the larval compound eye, or its transition into the adult eye structures. In order to address this knowledge deficit, I tested several hypotheses surrounding larval eye physiology and ontogeny using microspectrophotometry (MSP) and electroretinography (ERG). MSP was used to investigate visual pigment diversity in the retinas of different species of stomatopod larvae. Together with data previously published, these data provide further support that larvae possess a single spectral class of photoreceptor. Surprisingly, the peak spectral absorbance varied significantly among sympatric species, with four species falling into a short-wavelength and the remainder into a long-wavelength sensitivity class. These results may be explained by differences in behavioral ecology or by different developmental stages of individual test subjects. To investigate ontogenetic changes in retinal function, ERG intensity responses were measured from different stage retinas of a single species, Squilla empusa. Initial MSP data from transitioning retinas found no evidence of visual pigment absorption in newly emerged adult retinas, implying a putative delay in photoreceptive function. Robust ERG responses to light stimuli, however, were observed from the earliest presence of emerging adult retinas, rejecting this hypothesis. These data also suggest an increase in the response dynamics of stomatopod retinas with ontogeny as well as an increase in irradiance sensitivity during the double-retina phase. To investigate the visual ecology of stomatopod larval light-reflecting structures, I characterized the function and structure of eyeshine overlying the retina. In situ photography of larvae eyeshine demonstrated its function as a contrast reducer, or camouflage. Calculations of eyeshine reflectance spectra in their natural setting revealed novel, spectral matching with the background environment. Eyeshine structures were characterized via transmission electron microscopy (TEM) and identified as amorphous, three-dimensional photonic crystal arrays of spherical vesicles that coherently scatter light. The photonic mechanism of eyeshine production was tested using a modified Bragg-theory model and dimensions from TEM micrographs. These eyeshine data as well as data regarding the physiology of stomatopod larval vision provide a strong foundation for future investigations into the ontogeny of vision in stomatopod crustaceans