LUNAR ORIENTATION OF ORCHESTOIDEA CORNICULATA STOUT (AMPHIPODA)

Abstract

1. The orientation of Orchestoidea corniculata in direct moonlight, compared with the orientation when moonlight is reflected from a mirror, demonstrates that apparent lunar position is the dominant night-time orienting stimulus for this organism.2. An analysis of the effects of repeated photographic recording of the orientation indicates that this species changes its angle of lunar orientation and the scatter about the average as a result of repeated electronic photo-bulb flashes.3. Using only single observations of each group of animals, in order to avoid these artifacts, it was determined that this species, kept in total darkness for ten or more hours before observation, orients at a relatively constant angle with the moon, regardless of lunar stage or position. This result is not compatible with the hypothesis that O. corniculata possesses a continuously-operating lunar physiological rhythm similar to that claimed for Talitrus saltator.4. When the amphipods were exposed to sunset and moonrise on the night of observation, there was an indication of subsequently time-shifted angles of orientation with the moon. The tentative hypothesis of a single-cycle night-time orientation rhythm, re-initiated by the appropriate stimuli each night, would explain such observations.