The clock mechanism for circatidal rhythm has long been controversial, and its molecular basis is completely unknown. The mangrove cricket,
Apteronemobius asahinai
, shows two rhythms simultaneously in its locomotor activity: a circatidal rhythm producing active and inactive phases as well as a circadian rhythm modifying the activity intensity of circatidal active phases. The role of the clock gene
period
(
per
), one of the key components of the circadian clock in insects, was investigated in the circadian and circatidal rhythms of
A. asahinai
using RNAi. After injection of double-stranded RNA of
per
, most crickets did not show the circadian modulation of activity but the circatidal rhythm persisted without a significant difference in the period from controls. Thus,
per
is functionally involved in the circadian rhythm but plays no role, or a less important role, in the circatidal rhythm. We conclude that the circatidal rhythm in
A. asahinai
is controlled by a circatidal clock whose molecular mechanism is different from that of the circadian clock.
Role of Per3, a circadian clock gene, in brain development
