Ultraviolet vision in anemonefish improves color discrimination

In many animals, ultraviolet (UV) vision guides navigation, foraging, and communication, but few studies have addressed the contribution of UV vision to color discrimination, or behaviorally assessed UV discrimination thresholds. Here, we tested UV-color vision in an anemonefish (Amphiprion ocellaris) using a novel five-channel (RGB-V-UV) LED display designed to test UV perception. We first determined that the maximal sensitivity of the A. ocellaris UV cone was at ~386 nm using microspectrophotometry. Three additional cone spectral sensitivities had maxima at ~497, 515, and ~535 nm, which together informed the modelling of the fish’s color vision. Anemonefish behavioral discrimination thresholds for nine sets of colors were determined from their ability to distinguish a colored target pixel from grey distractor pixels of varying intensity. We found that A. ocellaris used all four cones to process color information and is therefore tetrachromatic, and fish were better at discriminating c..., Lens transmission of A. ocellaris
For the measurement of lens transmission in A. ocellaris, the lenses (n = 3 fish) were isolated from the hemisected eyecup and rinsed in PBS to remove any blood and vitreous. Spectral transmission (300–800 nm) was measured by mounting the lens on a drilled (1.0 mm diameter hole) metal plate between two fibers (50, 100 µm diameters) connected to an Ocean Optics USB4000 spectrometer and a pulsed PX2 xenon light source (Ocean Optics, USA). Light spectra were normalized to the peak transmission value at 700 nm, and lens transmission values were taken at the wavelength at which 50% of the maximal transmittance (T50) was attained. No pigmented ocular media was observed.
Photoreceptor spectral sensitivities of A. ocellaris
The spectral absorbance of A. ocellaris photoreceptors was measured using single-beam wavelength scanning microspectrophotometry (MSP). In summary, small pieces (~1 mm2) of tissue were excised from the eyes of two-hour dark-adapted fish, the..., All statistical analyses and color modelling were conducted using the statistical program R (v. 4.0.2). Color distances were calculated using the RNL model and plotted in a tetrahedral space using the package ‘PAVO 2’. Discrimination thresholds were determined by the point at which fish had a 0.5 probability of making a correct choice approximately at the inflection or steepest point of a sigmoid curve fitted to the behavioral data using the package ‘quickpsy’.
The effect of color sets on anemonefish discrimination thresholds was assessed using a linear mixed-effects model (LMM) run using function ‘lmer’ in the package ‘lme4’. Individual threshold ΔS value was treated as the response variable, color sets as the fixed factor, and fish ID was the random effect. A post-hoc, pair-wise analysis controlled for multiple comparisons of threshold ΔS values across all possible combinations of color sets using Bonferroni adjustment (p.adjust, R base package ‘stats’). Another set of LMMs tested the..., # Anemonefish have finer color discrimination in the ultraviolet

S2 Data.csv - Tables containing the absolute cone quantum catches (Q) calculated for both target colours and grey distractors (in separate tabs). 'u' = ultraviolet cone, 'm1' = medium-wavelength-sensitive cone 1, 'm2' = medium-wavelength-sensitive cone 2, and 'l' = long-wavelength-sensitive cone. Relative LED intensities are also provided for each colour and grey.

S3 Data.csv - Individual pre-bleach MSP measurements of photoreceptor spectral absorbance, and lens spectral transmission measurements in A. ocellaris. Photoreceptor light absorbance is reported across the wavelength range of 300 - 700nm. The title of each column/scan is given as the peak wavelength absorbance value as determined for the individual scan, where a number contained in brackets indicates whether >1 measurement of the same peak wavelength sensitivity was obtained. Best fit (A1/A2 based) visual pigment absorbance curve templates are also provided ...