Transitions in Dictyostelium discoideum behaviour: Influence of calcium and fluoride on slug phototaxis and thermotaxis

Abstract

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.