John S. Sparks; Robert C. Schelly; W. Leo Smith; Matthew P. Davis; Dan Tchernov; Vincent A. Pieribone; David F. Gruber

“ We have also reconstructed our current understanding of the phylogenetic distribution of biofluorescence for ray-finned fishes. The presence of yellow long-pass intraocular filters in many biofluorescent fish lineages and the substantive color vision capabilities of coral-reef fishes suggest that they are capable of detecting fluoresced light. We present species-specific emission patterns among closely related species, indicating that biofluorescence potentially functions in intraspecific communication and evidence that fluorescence can be used for camouflage. ”

“ Here we show that biofluorescence is not only phylogenetically widespread, but is also phenotypically variable across both cartilaginous and bony fishes, highlighting its evolutionary history and the possibility for discovery of numerous novel fluorescent proteins. Fish biofluorescence is especially common and morphologically variable in cryptically patterned coral-reef lineages. We identified 16 orders, 50 families, 105 genera, and more than 180 species of biofluorescent fishes. ”

“ Biofluorescence results from the absorption of electromagnetic radiation at one wavelength by an organism, followed by its reemission at a longer and lower energy wavelength, visually resulting in green, orange, and red emission coloration in marine organisms. ”

“ As Johnsen [41] justly notes, the field of biofluorescence is wide open for study and there have been far too few studies to date, most of which have focused on cnidarians. With the recent discovery of a novel fluorescent protein from a vertebrate [13] , we expect that biofluorescence in marine fishes will be the subjects of many future studies, from the level of proteins to whole organisms in their environment. ”

“ Worldwide, there are more than 8,000 species of fishes that inhabit coral reefs. Many reef fish species are known for their striking color patterns, whereas many others are cryptically patterned and appear well camouflaged. However, nearly nothing is known regarding the evolution or function of fluorescence in fishes. Only recently has a fluorescent protein, a novel fatty-acid-binding protein, been isolated from a vertebrate, a Japanese eel [18] . ”

“ Individuals of some other species were found to exhibit both alternating red and green fluorescent patterns (e.g., Fig. 1K) , whereas in other lineages, only the larval forms were observed to fluoresce (e.g., Fig. 1N, acanthurids) . Such observations in combination with pronounced interspecific variability in fluorescence emission pattern in otherwise similarly patterned taxa suggest that intraspecific communication is a function of biofluorescence in marine fishes, as has been shown in other organisms with complex visual systems (e.g., [8] ) . ”

“ Spectrally restricted illumination in the ocean provides unique lighting conditions for organisms to exploit fluorescence to produce visual contrast and patterns. In the marine environment, biofluorescence is highly prevalent in cnidarians (particularly Anthozoans) [2] , and also in a ctenophore [3] , copepods [4] , mantis shrimp [5] , amphioxus [6] and some fishes [7] . In addition, the photosynthetic apparatus associated with chlorophyll fluoresces red and provides a background of biofluorescence in areas of high algal growth on coral reefs. ”

“ The presence of biofluorescence in these deepwater taxa that spend their lives primarily in the dark, beyond the reach of the high-energy blue light necessary for excitation of fluorescence, is curious from a functional perspective. ”

“ Moonlight illumination in shallow ocean waters could potentially provide the appropriate excitation energy for green and red biofluorescence in fishes, and as a result, species-specific biofluorescent patterning may provide an added layer of species recognition during the spawning phase, when fishes are particularly vulnerable to predation.
Plot of emission spectra for representative green and red fluorescing marine fishes, also showing the spectra for enhanced green fluorescent protein (eGFP) for comparison.Key to species sampled: Ray (family Urotrygonidae, genus Urobatis) ”

“ The phylogeny presented in Figure 1 indicates that biofluorescence is phylogenetically widespread and phenotypically variable across ray-finned fishes (Actinopterygii) in terms of the diversity of patterns observed (Figs. 1, 3) , emission spectra (Fig. 4) , and intensity. We observed distinct variation among lineages and pronounced interspecific variation in emission patterns in closely related taxa that otherwise look nearly identical under white light. ”

“ Abstract The discovery of fluorescent proteins has revolutionized experimental biology. Whereas the majority of fluorescent proteins have been identified from cnidarians, recently several fluorescent proteins have been isolated across the animal tree of life. ”

“ Biofluorescence in these taxa potentially represents the ancestral condition in lineages whose shallower water relatives also exhibit biofluorescence (Figs. 1, 2) . Some bioluminescent (production and emission of light through a chemical reaction) deep-sea organisms have previously been shown to exhibit biofluorescence through a coupling of both bioluminescent and biofluorescent systems. ”

“ The phylogenetic analysis presented herein had a total of 5,238 base pairs including: one mitochondrial gene (cytochrome oxidase I, 812 bps) , and five protein-coding genes (glycosyltransferase gene, 732 bps; myosin heavy chain 6 alpha gene, 737 bps; pleiomorphic adenoma protein-like 2-like gene, 659 bps; recombination activating gene 1, 1403 bps; zic family member protein, 890 bps) . For each maximum likelihood analysis, the dataset was partitioned by individual gene fragments. ”

“ Images of reef fishes fluorescing in their natural habitat captured with a Red Epic video camera at night in the Solomon Islands. (A) A red fluorescing scorpionfish, Scorpaenopsis papuensis, perched on red fluorescing algae. ”