66.4 Saturday, Jan. 5 A circadian clock regulates both crawling and swimming in the nudibranch Melibe leonina KIROUAC, LE; NAIMIE, AA; BIXBY, KA; BOROSKI, CJ; LAWLOR, KE; RAMSEYER, TF; WATSON, III, WH; NEWCOMB, JM*; New England College; New England College; University of New Hampshire; New England College; New England College; New England College; University of New Hampshire; New England College firstname.lastname@example.org
Many animals exhibit circadian (~24 hours) rhythms of activity in natural light/dark (LD) conditions. If these rhythms persist in constant darkness (DD), this is indicative of an internal circadian clock. The purpose of this study was to determine if the nudibranch mollusc Melibe leonina expresses a circadian rhythm of locomotion, specifically crawling and swimming, in DD. Animals were videotaped for three days in LD, followed by at least five days of DD. Videos were quantified visually (n = 30), to determine how often animals swam, or using Ethovision software (n = 8), to measure distance crawled. These data were then visualized as actograms and analyzed using the program ClockLab to determine the periodicity of locomotor patterns. For crawling, 7 of 8 animals exhibited a circadian pattern of locomotion in DD (tau = 22.8 ± 1.3 hours). Swimming does not occur as often and only 11 of 30 animals regularly swam for the duration of the study. Of these 11 animals, 45% expressed a circadian rhythm of swimming in DD (tau = 23.5 ± 0.7 hrs). Regardless of the mode of locomotion, animals were typically most active just after sunset, or the time when sunset would have occurred in DD. These data indicate the presence of a circadian clock that influences both crawling and swimming behaviors in Melibe. Considering that the neural circuit underlying swimming in Melibe has been previously determined, these data suggest that Melibe may be a good model system for investigating how circadian clocks influence the daily expression of certain behaviors.