Meeting Abstract

38.4  Saturday, Jan. 5  Coexpression of Spectrally Distinct Opsins: A Novel Mechanism of Photoreceptor Tuning? DALTON, B. E. *; CRONIN, T. W.; CARLETON, K. L.; University of Maryland, Baltimore County

Detection of predators is a critical task that many animals accomplish visually. Because predators often appear as dark objects, their detection can be facilitated by making the background appear as bright as possible. According to the matching pigment hypothesis, this is accomplished by a receptor that is tuned to the background light spectrum. In nature, the color of the background differs with angle of view. Therefore, maximizing predator detection across the visual field requires multiple receptors tuned to heterogeneous backgrounds. Although cone cells sensitive to different wavelengths have been found in varying ratios across the retinas of diverse animals, the ecological function of this variation is largely unknown. Here, we tested whether opsins are expressed in retinal regions where they increase light absorbance of the corresponding backgrounds. Using in situ hybridization we found that cichlid fish coexpress spectrally distinct opsin genes in specific regions the retina. In these regions, coexpression increases light absorbance of the respective viewing backgrounds. Thus, opsin coexpression seems to tune the photoreceptors to their light environment. We confirmed the presence of cone cells containing opsin mixtures by microspectrophotometry. Interestingly, the frequency of coexpression varies among individuals, from just a small number of widely distributed double cones in some fish, to regionally abundant coexpression in others. Visual modeling is being used to evaluate the effect of coexpression on detection distance of dark objects such as predators. Ongoing work also includes light habitat manipulation to examine phenotypic plasticity and in situ experiments to determine the opsin expression patterns of wild-caught individuals.