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Visual pigments and oil droplets in diurnal lizards : a comparative study of Caribbean anoles
1
Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853,
USA
2
Department of Biology, Union College, Schenectady, NY 12308,
USA
3
Department of Biology, University of Virginia, Charlottesville, VA 22903,
USA
Present address: Department of Integrative and Molecular Neuroscience,
Division of Neuroscience and Psychological Medicine, Imperial College School
of Medicine, Charing Cross Hospital, Fulham Palace Road, London W6 8RF,
UK
Present address: Department of Anatomy, Physiology, and Genetics, Uniformed
Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda,
MD 20814, USA
* e-mail: ERL1{at}cornell.edu
Accepted 21 January 2002
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 A2 as its visual pigment chromophore, all
anoline species examined possessed at least four vitamin-A1-based
visual pigments with maximum absorbance (
max) at 564, 495,
455 and 365 nm. To the previously reported visual pigments for A.
carolinensis we add an ultraviolet-sensitive one with
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 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).
Key words: vision, microspectrophotometry, anoline, lizard, Anolis carolinensis, Polychrus marmoratus, visual pigment, oil droplet, photoreceptor
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