title: Behaviour of the plathelminth Symsagittifera roscoffensis under different light conditions and the consequences for the symbiotic algae Tetraselmis convolutae.
abstract: Symsagittifera roscoffensis is a plathelminth living in symbiosis with the green algae Tetraselmis convolutae. Host and symbiont are a model system for the study of endosymbiosis, which has so far mainly focused on their biochemical interactions. Symsagittifera roscoffensis is well known for its positive phototaxis that is hypothesized to optimize the symbiont's light perception for photosynthesis. In this study, we conducted a detailed analysis of phototaxis using light sources of different wavelength and brightness by videotracking. Furthermore, we compared the behavioural data with the electron transfer rate of the photosystem from cultured symbiotic cells. The symbiotic algae is adapted to low light conditions, showing a positive electron transfer rate at a photosynthetically active radiation of 0.112 µmol photons m(-2) s(-1), and S. roscoffensis showed a positive phototactic behaviour for light intensities up to 459.17 µmol photons m(-2) s(-1), which is not optimal regarding the needs of the symbiotic cells and may even harm host and symbiont. Red light cannot be detected by the animals and therefore their eyes seem not to be suitable for measuring the exact photosynthetically active radiation to the benefit of the photosymbionts.
authors: Department of Biophysics, Biological Institute, University of Rostock, Gertrudenstr. 11 A, Rostock 18057, Germany Department of Zoology, Institute of Biomaterials and Biomolecular Systems, University of Stuttgart, Pfaffenwaldring 57, Stuttgart 70569, Germany.
authors: Matthias
authors: M
authors: Nissen
authors: Institute of Zoology, University of Hohenheim, Garbenstr. 30, Stuttgart 70593, Germany.
authors: Denis
authors: D
authors: Shcherbakov
authors: Department of Plant Biotechnology, Institute of Biomaterials and Biomolecular Systems, University of Stuttgart, Pfaffenwaldring 57, Stuttgart 70569, Germany.
authors: Arnd
authors: A
authors: Heyer
authors: Department of Zoology, Institute of Biomaterials and Biomolecular Systems, University of Stuttgart, Pfaffenwaldring 57, Stuttgart 70569, Germany.
authors: Franz
authors: F
authors: Brümmer
authors: Department of Zoology, Institute of Biomaterials and Biomolecular Systems, University of Stuttgart, Pfaffenwaldring 57, Stuttgart 70569, Germany ralph.schill@bio.uni-stuttgart.de.
authors: Ralph O
authors: RO
authors: Schill
mesh_terms: D000818:Animals; D000460:Chlorophyta / Q000502:physiology / Q000528:radiation effects*; D008027:Light; D009068:Movement / Q000528:radiation effects; D010788:Photosynthesis; D010986:Platyhelminths / Q000502:physiology / Q000528:radiation effects*; D013559:Symbiosis
keywords: Endosymbionts; Endosymbioses; Host; Photoautotroph; Phototaxis