Abstract:  Photosensitive behaviors and circadian rhythms are well documented in reef-building corals, yet photoreceptive structures and opsins have not been described in these organisms.  Here, I provide several lines of evidence for opsin-based photosensitivity in coral larvae. Behavioral experiments with two Caribbean corals, Porites astreoides and Acropora palmata demonstrated that larvae settle and metamorphose at a greater frequency on red substrata than on similar substrata of other colors. Electroretinographic recordings from several species of planulae confirm photosensitivity and indicate that the spectral sensitivity peaks of coral photoreceptors are shifted towards the orange-red region of the visible light spectrum, similar to the spectra (fluorescence and reflectance) of preferred artificial (plastic) and natural (crustose coralline algae) settlement substrata. Using a PCR-based approach, I cloned three full-length opsins from A. palmata larvae. These proteins (Acropsins 1-3) resemble both vertebrate and invertebrate opsins, e.g., contain characteristic lysine residue known to couple to retinal. Immunofluorescence confocal microscopy showed that Acropsin 1 appears to be localized in the larval gastroderm, and Acropsin 2 is localized in a small population of epithelial cells, with an aboral expression pattern. To demonstrate light sensitivity, I cloned several coral G proteins – orthologs of vertebrate Gi, Go and Gq (72-84% identity) and a novel coral G protein that has 39% identity to Gi and some unique features. I over-expressed the acropsins in mammalian cells, reconstituted with 11-cis-retinal and showed they can activate some of the coral G proteins in a light-dependent manner.

Biography:  Dr. Benjamin M. Mason completed his Ph.D. at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science and a brief postdoc at the University of Miami, Miller School of Medicine.  He currently resides in Townsville, QLD. His research centers around coral larval biology and settlement ecology, but specific areas of focus include efforts to understand the molecular mechanisms involved in larval sensory biology and the physiological effects of climate change on the early life history stages of corals.