title: Red fluorescence of the triplefinTripterygion delaisiis increasingly visible against background light with increasing depth.
abstract: The light environment in water bodies changes with depth due to the absorption of short and long wavelengths. Below 10 m depth, red wavelengths are almost completely absent rendering any red-reflecting animal dark and achromatic. However, fluorescence may produce red coloration even when red light is not available for reflection. A large number of marine taxa including over 270 fish species are known to produce red fluorescence, yet it is unclear under which natural light environment fluorescence contributes perceptively to their colours. To address this question we: (i) characterized the visual system ofTripterygion delaisi,which possesses fluorescent irides, (ii) separated the colour of the irides into its reflectance and fluorescence components and (iii) combined these data with field measurements of the ambient light environment to calculate depth-dependent perceptual chromatic and achromatic contrasts using visual modelling. We found that triplefins have cones with at least three different spectral sensitivities, including differences between the two members of the double cones, giving them the potential for trichromatic colour vision. We also show that fluorescence contributes increasingly to the radiance of the irides with increasing depth. Our results support the potential functionality of red fluorescence, including communicative roles such as species and sex identity, and non-communicative roles such as camouflage.
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, Department of Biology, Faculty of Science , University of Tübingen , 72076 Tübingen , Germany.
authors.forename: Pierre-Paul
authors.identifier: 0000-0001-5984-2331
authors.initials: PP
authors.lastname: Bitton
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, Department of Biology, Faculty of Science , University of Tübingen , 72076 Tübingen , Germany.
authors.forename: Ulrike K
authors.initials: UK
authors.lastname: Harant
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, Department of Biology, Faculty of Science , University of Tübingen , 72076 Tübingen , Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Fritsch
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, Department of Biology, Faculty of Science , University of Tübingen , 72076 Tübingen , Germany.
authors.forename: Connor M
authors.identifier: 0000-0002-9954-6403
authors.initials: CM
authors.lastname: Champ
authors.affiliation: School of Biological Sciences , University of Bristol , Bristol BS8 1TQ , UK.
authors.forename: Shelby E
authors.identifier: 0000-0001-6447-4713
authors.initials: SE
authors.lastname: Temple
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, Department of Biology, Faculty of Science , University of Tübingen , 72076 Tübingen , Germany.
authors.forename: Nico K
authors.initials: NK
authors.lastname: Michiels
keywords: fluorescence; intraspecific signal; photoreceptor; visual communication; visual model