Diaphototaxis and gravitaxis in a freshwater Cryptomonas
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Updated: Oct 4, 2026

Observation of Photobehavior in Chlamydomonas reinhardtii
Published on: May 6, 2022
E Rhiel1, D P Hader, W Wehrmeyer
1Fachbereich Biologie-Botanik, Karl-von-Frisch-Str., Federal Republic of Germany.
Abstract:
Phototaxis and gravitaxis are characterized in a freshwater species of the flagellate Cryptomonas. The phototactic orientation in this limnetic species is unusual and differs from all other Cryptomonas species studied so far: At both low (< or = 1O W m-2) and higher fluence rates it orients perpendicular to the light beam (diaphototaxis) while another freshwater Cryptomonas species (strain CR-1) is restricted to positive phototaxis and the marine species, C. maculata, shows both a positive and a more pronounced negative phototaxis. The mechanism of light direction detection seems to depend on a periodic shading or irradiation mechanism as confirmed by the disturbance of phototaxis in the presence of high viscosity media. In addition, this freshwater species possesses a rather pronounced negative gravitaxis which is only partially modified by phototaxis. The ecological consequences of this behavior are discussed.
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