Meeting Abstract
The spectral tuning properties of the whale shark (Rhincodon typus), basking shark (Cetorhinus maximus), and megamouth shark (Megachasma pelagios) rod (Rh1) and long-wavelength sensitive (LWS) cone visual pigments were examined to determine whether these retinal pigments have adapted to the broadband light spectrum available for surface foraging, or to the narrowband blue-shifted light spectrum available at depth. Recently published whale shark Rh1 and LWS cone opsin genes were used to design primers for amplification and sequencing of the opsin proteins from basking and megamouth sharks. Basking and megamouth shark Rh1 and LWS cone coding sequences were PCR amplified and sequenced to identify amino acid residues critical for spectral tuning. The predicted absorbance maxima (λmax) for the whale, basking, and megamouth shark Rh1 visual pigments were 496 nm, 496 nm, and 486 nm, respectively. The deduced amino acid sequence for both the whale and basking shark LWS cone opsins resulted in predicted λmax values near 500 nm. Although Rh1 λmax values near 500 nm are typical of terrestrial vertebrates and surface foraging fish, it is uncommon for vertebrate LWS cone pigments to be so greatly blue-shifted. We propose that the spectral tuning properties of the Rh1 and LWS cone pigments in whale and basking sharks are most likely an adaptation to the broadband light spectrum available at the surface, while the megamouth shark Rh1 pigment is most likely an adaptation to the narrowband light spectrum available in deeper waters.
