Thermotaxis behavior. (A) Configuration of assay plate used in this study. Temperature at the center of region B was controlled and formed a radial temperature gradient. Worms were placed at the center of region C. (B) Temperature gradient of assay plate. (C) Time course of thermotaxis index. RT, peak (e.g., 20°C, 15°C) indicates that room temperature was 20°C and the peak temperature was 15°C. Each data point is presented as the mean ± standard error of the mean (SEM). (D) Relationship between thermotaxis index and temperature gradient. Ordinate indicates the peak values of thermotaxis indices in the worms cultivated at defined temperatures. Steepness of temperature gradient is indicated in the abscissa as a value of controlled temperature at region B (ConT) minus room temperature (RT). (E) Relationship between thermotaxis behavior and temperature gradient. Index (ordinate) indicates the rate of migration toward the side of the plate containing the temperature-controlled region. Abscissa is the same as shown in (D). Arrowheads in D and E indicate indices toward the region of 23°C (white) and toward the region of 25°C (black) in the worms cultivated at 25°C.