University of New Hampshire Scholars\u27 Repository
Abstract
The American lobster, Homarus americanus, is a decapod crustacean whose daily nocturnal rhythms of activity are driven, in part, by an internal biological clock. While this circadian clock is capable of producing a rhythm of approximately 24 hours on its own, it can also be entrained to light:dark cycles. Recent findings in our laboratory suggest that lobsters have photosensitive neurons throughout their nervous system (extra-ocular photoreceptors). The objective of this research was to test the hypothesis that these extra-ocular photoreceptors aid in entraining their daily rhythm of activity. First, the locomotion of juvenile American lobsters was measured in trials under a normal 24 hour light:dark cycle. Then, after this “control” period, the lobsters’ eyes were painted with black nail polish and their activity was monitored under the same conditions. The lobsters were also exposed to DD conditions with their eyes covered in one of the trials. During the control LD cycle, lobsters expressed increased locomotion at night, demonstrating their daily rhythm. The DD cycle had a consistent rhythm with an elongated period of activity. Interestingly, half of the lobsters continued to follow the same pattern of activity despite the visual impairment and half expressed a diurnal rhythm. Although there was variation in the locomotor activity, a periodicity of ~24 hours was maintained throughout the LD cycles. This indicates that H. americanus receives photoperiod input from both their eyes and extra-ocular photoreceptors that help synchronize their locomotor activity to LD cycles
