Circannual Rhythms in Insects

Abstract

Certain fi sh exhibit lunar and semilunar reproductive activities that are repeated at regular intervals of 1 month and 2 weeks, respectively. Fish with the lunar cycle exhibit spawning around a selective moon phase, whereas those with the semilunar cycle repeat spawnings twice within a month. Environmental changes in moonlight or tides may be involved in the synchronization of fi sh reproductive activity. Spawning of the goldlined spinefoot Siganus guttatus , a lunar spawner around the fi rst quarter moon, is disrupted under constant moonlight conditions. Exposing fi sh to moonlight around the full moon resulted in suppression of melato- nin, suggesting the perception and utilization of changes in moonlight for synchrony. Of the clock genes examined, Period ( Per2 ) in the pineal organ was higher at mid- night around the full moon than the new moon, whereas Cryptochrome ( Cry1 and Cry3 ) in the brain peaked around the fi rst quarter moon. Although circalunar- specifi c genes have not yet been identifi ed in any organism, some elements of the circadian system are likely involved in the exertion of lunar-related reproductive activities.