Visual pigments and oil droplets in diurnal lizards: a comparative study of Caribbean anoles.
Loew ER., Fleishman LJ., Foster RG., Provencio I.
We report microspectrophotometric (MSP) data for the visual pigments and oil droplets of 17 species of Caribbean anoline lizard known to live in differing photic habitats and having distinctly different dewlap colors. The outgroup Polychrus marmoratus was also examined to gain insight into the ancestral condition. Except for Anolis carolinensis, which is known to use vitamin A(2) as its visual pigment chromophore, all anoline species examined possessed at least four vitamin-A(1)-based visual pigments with maximum absorbance (lambda(max)) at 564, 495, 455 and 365 nm. To the previously reported visual pigments for A. carolinensis we add an ultraviolet-sensitive one with lambda(max) at 365 nm. Five common classes of oil droplet were measured, named according to apparent color and associated with specific cone classes - yellow and green in long-wavelength-sensitive (LWS) cones, green only in medium-wavelength-sensitive (MWS) cones and colorless in short-wavelength-sensitive (SWS) and ultraviolet-sensitive (UVS) cones. MSP data showed that the colorless droplet in the SWS cone had significant absorption between 350 and 400 nm, while the colorless droplet in the UVS cone did not. The pattern for Polychrus marmoratus was identical to that for the anoles except for the presence of a previously undescribed visual cell with a rod-like outer segment, a visual pigment with a lambda(max) of 497 nm and a colorless oil droplet like that in the UVS cones. These findings suggest that anoline visual pigments, as far as they determine visual system spectral sensitivity, are not necessarily adapted to the photic environment or to the color of significant visual targets (e.g. dewlaps).