PHASE RELATIONSHIP BETWEEN OCULAR AND BEHAVIORAL CIRCADIAN-RHYTHMS INBULLA-GOULDIANA EXPOSED TO DIFFERENT PHOTOPERIODS

To determine whether the ocular circadian pacemakers of the marine sna il Bulla gouldiana exert phase control over the circadian rhythm in lo comotor activity, we measured the phase angles for entrainment of the ocular pacemakers and the activity rhythm on four different photoperio ds: L:D 15:9, 12:12, 9:15, and 4:20. We found that the phase angle for ocular entrainment was progressively advanced relative to dawn as pho toperiod decreased, although the phase was fixed relative to the middl e of the day. In contrast, activity began near dusk on all photoperiod s. On subsequent release into constant conditions, the free-running lo comotor activity commenced near the time of previous activity onset. T hus, activity phase on light cycles represents the entrainment of a li ght sensitive pacemaker. The resulting lability in phase between ocula r and behavioral rhythms in Bulla exposed to light cycles suggests tha t the ocular pacemakers are not the only determinants of locomotor act ivity phase in Bulla.