Spectral tuning by opsin coexpression in retinal regions that view different parts of the visual field
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2014-10-02
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Dalton BE, Loew ER, Cronin TW, Carleton KL. 2014 Spectral tuning by opsin coexpression in retinal regions that view different parts of the visual field. Proc. R. Soc. B 281: 20141980. http://dx.doi.org/10.1098/rspb.2014.1980
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Abstract
Vision frequently mediates critical behaviours, and photoreceptors must
respond to the light available to accomplish these tasks. Most photoreceptors
are thought to contain a single visual pigment, an opsin protein bound to a
chromophore, which together determine spectral sensitivity. Mechanisms of
spectral tuning include altering the opsin, changing the chromophore and
incorporating pre-receptor filtering. A few exceptions to the use of a single
visual pigment have been documented inwhich a singlemature photoreceptor
coexpresses opsins that form spectrally distinct visual pigments, and in these
exceptions the functional significance of coexpression is unclear.Herewe document
for the first time photoreceptors coexpressing spectrally distinct opsin
genes in a manner that tunes sensitivity to the light environment. Photoreceptors
of the cichlid fish, Metriaclima zebra, mix different pairs of opsins in
retinal regions that view distinct backgrounds. The mixing of visual pigments
increases absorbance of the corresponding background, potentially aiding the
detection of dark objects. Thus, opsin coexpressionmay be a novel mechanism
of spectral tuning that could be useful for detecting prey, predators and mates.
However, our calculations show that coexpression of some opsins can hinder
colour discrimination, creating a trade-off between visual functions.