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

B.F. F. Simoes, F.L. L. Sampaio, E.R. R. Loew, K.L. L. Sanders, R.N. N. Fisher, N.S. S. Hart, David M. Hunt, Julian C. Partridge, D.J. J. Gower

Research output: Contribution to journalArticlepeer-review

30 Citations (Web of Science)


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, rh1, sws1 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.
Original languageEnglish
Article number20152624
Pages (from-to)1-8
Number of pages8
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1823
Publication statusPublished - 27 Jan 2016


Dive into the research topics of 'Multiple rod–cone and cone–rod photoreceptor transmutations in snakes: evidence from visual opsin gene expression'. Together they form a unique fingerprint.

Cite this