Abstracts

Bioluminescence is the capability to emit visible light thanks to a biochemical reaction. About 80% of the known luminous species live in the marine environment. Among luminous substrates, coelenterazine is the most widespread luciferin described in at least eight phyla. The broad phylogenetic distribution of this light-emitting molecule led to the hypothesis of its dietary acquisition, demonstrated in one jellyfish, one lophogastrid shrimp, and one brittle star species. The European brittle star A. filiformis is a model species within Ophiuroidea, the dominant class of luminous Echinoderms. The latter emits a blue light via a Renilla-like luciferase dependent on a dietary acquisition of the coelenterazine. Nevertheless, questions remain concerning this coelenterazine trophic acquisition process: (i) Do seasonal variations of luminescence capabilities exist? (ii) How long can brittle star luminous capabilities persist after a single boost of coelenterazine? (iii) does the luciferase expression change in photogenic tissues after the exogenous supply of coelenterazine? A multidisciplinary analysis with luminometric measurements, luciferase immunolabelling, and histological visualization was undertaken to answer these questions.Our results highlighted (i) no seasonal variation in A. filiformis luminous capabilities involving a continuous supply from prey containing coelenterazine, (ii) the coelenterazine availability in the brittle star diet is the only limiting factor for the bioluminescent reaction, (iii) a green autofluorescence signal attributed to coelenterazine over the luciferin acquisition, (iv) the luciferase is expressed throughout the brittle star life. Moreover, the ultrastructure description supports the hypothesis of a pigmented sheath transmitting light to the tip of the spine. All these insights improve our knowledge of the bioluminescence phenomenon of this suspensive feeder brittle star.