Multiple rod–cone and cone–rod photoreceptor transmutations in snakes: Evidence from visual opsin gene expression

Proceedings of the Royal Society B
By: , and 

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Abstract

In 1934, Gordon Walls forwarded his radical theory of retinal photoreceptor ‘transmutation’. This proposed that rods and cones used for scotopic and photopic vision, respectively, were not fixed but could evolve into each other via a series of morphologically distinguishable intermediates. Walls' prime evidence came from series of diurnal and nocturnal geckos and snakes that appeared to have pure-cone or pure-rod retinas (in forms that Walls believed evolved from ancestors with the reverse complement) or which possessed intermediate photoreceptor cells. Walls was limited in testing his theory because the precise identity of visual pigments present in photoreceptors was then unknown. Subsequent molecular research has hitherto neglected this topic but presents new opportunities. We identify three visual opsin genes, rh1sws1 and lws, in retinal mRNA of an ecologically and taxonomically diverse sample of snakes central to Walls' theory. We conclude that photoreceptors with superficially rod- or cone-like morphology are not limited to containing scotopic or photopic opsins, respectively. Walls' theory is essentially correct, and more research is needed to identify the patterns, processes and functional implications of transmutation. Future research will help to clarify the fundamental properties and physiology of photoreceptors adapted to function in different light levels.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Multiple rod–cone and cone–rod photoreceptor transmutations in snakes: Evidence from visual opsin gene expression
Series title Proceedings of the Royal Society B
DOI 10.1098/rspb.2015.2624
Volume 283
Issue 1823
Year Published 2016
Language English
Publisher The Royal Society
Contributing office(s) Western Ecological Research Center
Description 20152624, 8 p.
Online Only (Y/N) N
Additional Online Files (Y/N) N