Retinal photoreceptors and visual pigments in Boa constrictor imperator

The photoreceptors of Boa constrictor, a boid snake of the subfamily Boinae , were examined with scanning electron microscopy and microspectrophotometr y. The retina of B. constrictor is duplex but highly dominated by rods, con es comprising 11% of the photoreceptor population. The rather tightly packe d rods have relatively long outer segments with proximal ends that are some what tapered. There are two morphologically distinct, single cones. The mos t common cone by far has a large inner segment and a relatively stout outer segment. The second cone, seen only infrequently, has a substantially smal ler inner segment and a finer outer segment. The visual pigments of B. cons trictor are virtually identical to those of the pythonine boid, Python regi us. Three different visual pigments are present, all based on vitamin A,. T he visual pigment of the rods has a wavelength of peak absorbance (lambda ( max)) at 495 +/- 2 mn. The visual pigment of the more common, large cone ha s a lambda (max) at 549 +/- 1 mn. The small, rare cone contains a visual pi gment with lambda (max) at 357 +/- 2 nm, providing the snake with sensitivi ty in the ultraviolet. We suggest that B. constrictor might employ UV sensi tivity to locate conspecifics and/or to improve hunting efficiency. The dat a indicate that wavelength discrimination above 430 nm would not be possibl e without some input from the rods. (C) 2001 Wiley-Liss, Inc.