Melissa G. Meadows; Nils Anthes; Sandra Dangelmayer; Magdy A. Alwany; Tobias Gerlach; Gregor Schulte; Dennis Sprenger; Jennifer Theobald; Nico K. Michiels

“ Alternative measures of fluorescence brightness (maximum or mean peak emission per fish, or mean integrated total emission per fish) yielded qualitatively identical results.
Fluorescent emission spectra of the eight study species averaged and sum-normalized across all measured individuals using the maximum curve for each individual. All species show a peak emission in the spectral range where absorption by water increases rapidly (cf. figure 1) . ”

“ We suspect that the observed difference between the two depths involves differences in the number of melanophores covering the iris, the number of fluorescent chromatophores and/or the concentration of fluorescent pigment within the fluorescent chromatophores. Because we did not correct for the size of the fluorescent patch, we cannot exclude that fluorescent patch size may also have contributed to the observed effect. The differences in fluorescence brightness could originate from phenotypic plasticity during development or in the adult stage, or due to local genetic adaptation. ”

“ This feature is unique to fluorescence and other forms of luminescence (e.g. chemi- or bioluminescence [16] ) . Virtually all animal colours, however, merely reflect or transmit light that is not absorbed. Consequently, they display a down-sampled subset of the ambient spectrum, which is why they are called subtraction colours. This applies to pigments as well as structural colours [17] , [18] . The key question is under what conditions additive fluorescent coloration can be significant for colour vision, given the evolutionary success of subtraction colours. ”

“ As a consequence, even weak red fluorescence may become visible to an observer with the appropriate sensitivity. This is due to the way in which eyes perceive chromatic contrast; it depends on the ratios of cone photoreceptor types that are stimulated by light coming from an object compared with an adjacent object or background [20] , [28] . Hence, even when quantitatively weak, red fluorescent structures could produce a perceptible colour contrast against the cyan background of the stenospectral zone. ”

“ The eight study species under fluorescence and white light conditions. The first two columns were taken in the laboratory under standard fluorescence photography conditions, showing the individuals with the minimum (left column) and maximum (right column) fluorescence brightness among all sampled individuals. The third column shows individuals under standard white light conditions in the laboratory. Pictures were all taken under the same light conditions, explaining slight overexposure effects in species with strongly fluorescent eyes (triplefins H. striata and T. delaisi) . ”

“ Each new fish measurement series included a control measurement of a Labsphere Spectralon Fluorescence Standard (type USFS-336–010) to check for fluctuations in measurement sensitivity. Spectrometer integration times were usually 800 ms, but adjusted to shorter integration times when emission intensities exceeded the dynamic range of the spectrometer (e.g. in B. natans) . All final measurements were uniformly expressed as counts ms−1 nm−1. ”

“ Every dive focused on a single species. We usually reached our goal of approximately 10 individuals at each target depth on a single dive with two to four divers. We sampled at or below −20 m during the first half of the dive and at or above −5 m during the second half of the dive. ”

“ Spectrometric measurements were taken with an Ocean Optics QE65000 spectrometer for fluorescence and a bifurcated OceanOptics QR600–7-UV125BX fibre optics cable with a single saltwater proof tip in which six peripheral bundles of glass fibres emit the excitation light and one central bundle of glass fibres collects the emitted light. Excitation light was generated using a green laser (ThorLabs CPS532, a 532 nm laser diode module with an AHF narrow-band laser clean-up filter ZET 532/10) and guided into the illumination arm of the bifurcated fibre. ”

“ In five species (B. natans, C. nigripectus, E. guttata, E. zebrina and F. cf. duospilus) , individuals from shallow water tended to be larger on average than those from deeper water (Welch's t-test, all p < 0.088) with the reverse pattern in T. delaisi (p = 0.026) and no difference in P. micheli and H. striata (all p > 0.42) . ”

“ Endogenous green fluorescent protein (GFP) in amphioxus. Biol. Bull. 213, 95–100 (doi:10.2307/25066625) pmid:17928516↑ Field SF, Bulina MY, Kelmanson IV, Bielawski JP, Matz MV. 2006. Adaptive evolution of multicolored fluorescent proteins in reef-building corals. J. Mol. Evol. 62, 332–339 (doi:10.1007/s00239-005-0129-9) pmid:164749841 2 3 Johnsen S. 2012. The optics of life: a biologist’s guide to light in nature. Princeton, NJ: Princeton University Press↑ Endler JA. 1990. On the measurement and classification of colour in studies of animal colour patterns. Biol. J. Linn. Soc. ”