Meeting Abstract
Different parts of the visual field are viewed by distinct regions of the retina which can differ in sensitivity. Variation in spectral sensitivity within the retina is documented in a growing number of taxa. In such species, the appearance of objects and signals will depend on the sensitivity of the retinal region that detects them. Spectral sensitivity relies on the visual pigments, composed of an opsin protein bound to a chromophore. Altering either molecule can modify the pigment’s absorbance spectrum. We use dual-labeling fluorescent in situ hybridization to determine the distribution of opsins across the retinas of cichlid fishes in their single cones and each member of their double cones (pairs of partially fused cone cells). African cichlids are noteworthy because they form new species rapidly, due in part to coevolution of spectral sensitivity and male nuptial coloration. We found that in Metriaclima zebra, each cone class mixes a different pair of opsins in a retinal region that views a distinct background. This opsin coexpression increases absorbance of the corresponding backgrounds, and modeling indicates this could facilitate detection of dark objects. Thus, opsin coexpression may be a novel mechanism of spectral tuning. However, our calculations indicate coexpression of some opsins can hinder color discrimination, creating a trade-off between visual functions. We also demonstrate that the location and relative proportion of opsins within the M. zebra retina can be altered by the rearing light environment. The background spectra at different angles in a cichlid’s environment might influence the specific pattern of spectral sensitivity that develops across its retina, biasing signal evolution and contributing to the rapid radiation of this diverse group of fishes.
