The dual rod system of amphibians supports colour discrimination at the absolute visual threshold

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Yovanovich , C A M , Koskela , S M , Nevala , N , Kondrashev , S L , Kelber , A & Donner , K 2017 , ' The dual rod system of amphibians supports colour discrimination at the absolute visual threshold ' , Philosophical Transactions of the Royal Society. Biological Sciences , vol. 372 , no. 1717 , 20160066 . https://doi.org/10.1098/rstb.2016.0066

Title: The dual rod system of amphibians supports colour discrimination at the absolute visual threshold
Author: Yovanovich, Carola A. M.; Koskela, Sanna M.; Nevala, Noora; Kondrashev, Sergei L.; Kelber, Almut; Donner, Kristian
Contributor: University of Helsinki, University of Helsinki
University of Helsinki, Biosciences
Date: 2017-04-05
Language: eng
Number of pages: 10
Belongs to series: Philosophical Transactions of the Royal Society. Biological Sciences
ISSN: 0962-8436
URI: http://hdl.handle.net/10138/221322
Abstract: The presence of two spectrally different kinds of rod photoreceptors in amphibians has been hypothesized to enable purely rod-based colour vision at very low light levels. The hypothesis has never been properly tested, so we performed three behavioural experiments at different light intensities with toads (Bufo) and frogs (Rana) to determine the thresholds for colour discrimination. The thresholds of toads were different in mate choice and prey-catching tasks, suggesting that the differential sensitivities of different spectral cone types as well as task-specific factors set limits for the use of colour in these behavioural contexts. In neither task was there any indication of rod-based colour discrimination. By contrast, frogs performing phototactic jumping were able to distinguish blue from green light down to the absolute visual threshold, where vision relies only on rod signals. The remarkable sensitivity of this mechanism comparing signals from the two spectrally different rod types approaches theoretical limits set by photon fluctuations and intrinsic noise. Together, the results indicate that different pathways are involved in processing colour cues depending on the ecological relevance of this information for each task. This article is part of the themed issue 'Vision in dim light'.
Subject: Bufo
Rana
photoreceptors
behaviour
visual threshold
colour vision
RETINAL GANGLION-CELLS
ADULT ANURAN AMPHIBIANS
FROG RANA-TEMPORARIA
TOAD BUFO-BUFO
GREEN RODS
DARK NOISE
RED RODS
PIGMENTS
VISION
LIGHT
3111 Biomedicine
1182 Biochemistry, cell and molecular biology
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