Abstract
Bioluminescence is a fascinating phenomenon and can be found in many different organisms including fish. It has been suggested that bioluminescence is used for example for defense, prey attraction, and for intraspecific communication to attract for example sexual partners. The flashlight fish, Anomalops katoptron (A. katoptron), is a nocturnal fish that produces bioluminescence and lives in shallow waters, which makes it ideal for laboratory studies. In order to understand A. katoptron’s ability to detect bioluminescent light (480 to 490 nm) at night, we characterized the visual system adaptation of A. katoptron using phylogenetic, electrophysiological and behavioral studies. We found that the retinae of A. katoptron contain rods and sparse cones. A. katoptron retinae express two main visual pigments, rhodopsin (RH1), and to a lesser extent, rhodopsin-like opsin (RH2). Interestingly, recombinant RH1 and RH2 are maximally sensitive to a wavelength of approximately 490 nm light (λmax), which correspond to the spectral peak of in vivo electroretinogram (ERG) measurements. In addition, behavioral assays revealed that A. katoptron is attracted by low intensity blue but not red light. Collectively, our results suggest that the A. katoptron visual system is optimized to detect blue light in the frequency range of its own bioluminescence and residual starlight.
Highlights
Bioluminescence has evolved in many different organisms such as bacteria, fungi, flies and fishes [1]
We found that A. katoptron retinae contain rods, very few cones and express mRNAs encoding for two types of visual pigments (i.e. Rh1 and Rh2)
The retina of Anomalops katoptron consists of rods and sparse cones To understand the organization of the A. katoptron visual system we performed a histological analysis of their retina and compared the laminar organization of A. katoptron to goldfish Carassius auratus (C. auratus) retina
Summary
Bioluminescence has evolved in many different organisms such as bacteria, fungi, flies and fishes [1]. It is produced by an oxygen dependent reaction involving a catalyzing enzyme (luciferase) and a complex light-emitting molecule (luciferin) to produce light. Bioluminescence has evolved independently at least 40 times during evolution [2]. The emission of light is normally in the blue/green spectral range (e.g. 440 nm in amphipod shrimps Scina rassicornis and Scina borealis and 470 nm in the jellyfish Aequorea victoria) with some red-shifted exceptions found in crustaceans and tunicates [3]. Bioluminescence often occurs in the marine environment in particular in the deep sea rather than in benthic or shallow waters. Bioluminescent light is often used by fish to detect
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