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Transitions in Dictyostelium discoideum behaviour: influence of calcium and fluoride on slug phototaxis and thermotaxis
U. Dohrmann, P.R. Fisher, M. Bruderlein, K.L. Williams


Phototaxis and thermotaxis by slugs of Dictyostelium discoideum show transitions that result in bimodality in phototaxis and temperature-dependent orientation up or down temperature gradients. New steps in the sensory transduction chain for these kinds of behaviour are elucidated from studies using inorganic salts (Ca2+, EGTA, KF) and several mutants. KF enhances bimodality of phototaxis, improves the accuracy of thermotaxis, and affects the transition temperatures from positive to negative thermotaxis. Changing the Ca2+ concentration has effects on both phototaxis and thermotaxis. At low Ca2+ concentrations phototaxis and thermotaxis are enhanced. In the presence of EGTA or high concentrations of Ca2+ phototaxis becomes bimodal, thermotaxis is impaired and spontaneous turning is suppressed. These results obtained by changing Ca2+ concentrations are analogous to those obtained previously with sensory transduction mutations, which coordinately affect phototaxis and thermotaxis.