title: Diaphototaxis and gravitaxis in a freshwater Cryptomonas.
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.
authors.affiliation: Fachbereich Biologie-Botanik, Karl-von-Frisch-Str., Federal Republic of Germany.
authors.forename: E
authors.initials: E
authors.lastname: Rhiel
authors.forename: D P
authors.initials: DP
authors.lastname: Hader
authors.forename: W
authors.initials: W
authors.lastname: Wehrmeyer
mesh_terms: D056890:Eukaryota / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D005583:Fourier Analysis; D005618:Fresh Water / Q000382:microbiology*; D018522:Gravitropism; D007091:Image Processing, Computer-Assisted; D008027:Light; D018715:Microscopy, Video; D009068:Movement / Q000528:radiation effects*; D009949:Orientation / Q000528:radiation effects*; D018462:Photobiology; D012623:Seawater; D014871:Water Microbiology