Bimodality in the Nocturnal Behavior of the Giant Land Snail, Achatina fulica

Abstract

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 1-2 hr after the onset of darkness and a later peak after nearly 6 hr. The activity rhythms were able to follow a 6 hr 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 multios-cillator circadian organization which shows monophasic or biphasic entrainment under the LD cycles. —circadian activity rhythm; entrainment; LD cycle ; Achatina fulica. © 1990, Tohoku University Medical Press. All rights reserved.