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OGASAWARA, T. and TASAKI, K. Bimodality in the Nocturnal Behavior of the Giant Land Snail, Achatina fulica. Tohoku J. Exp. Med., 1990, 161 (2), 129-135 -Entrainment and phase advance of the circadian locomotor rhythms in the giant land snail, Achatina fulica, were examined by a running wheel method. The mean activity patterns in three light-dark (LD) cycles (LD 14:10, LD12:12, LD 10:14) were characterized by bimodal peaks, namely an initial major peak 1-2hr after the onset of darkness and a later peak after nearly 6hr. The activity rhythms were able to follow a 6hr phase advance shift of the LD 14:10 cycle with transients, accompanied by shortening or splitting of the activity time. When splitting occurred, the initial component showed phase advancement in the dark and phased to lights-off whereas the later one phased to lights-on, with post-dawn activity being suppressed by light. These results suggest the presence of multioscillator circadian organization which shows monophasic or biphasic entrainment under the LD cycles. |
