Meeting Abstract
P1.97 Sunday, Jan. 4 Do Circatidal or Circalunidian Clocks Control Locomotor Rhythms in the American Horseshoe Crab? RAMBERG PIHL, Nicole/C*; WATSON, Winsor/H; CHABOT, Christopher/C; Plymouth State University; University of New Hampshire; Plymouth State University ncrambergpihl@mail.plymouth.edu
Like many other inter-tidal dwellers or visitors, the American Horseshoe Crab, Limulus polyphemus, expresses endogenous locomotor activity rhythms that can be synchronized to the tides. While these biological rhythms have been long recognized, the nature of the timing system controlling them is somewhat controversial: the system could theoretically be comprised of either two 24.8h (circalunidian), or one 12.4h (circatidal) clock and there is evidence that seemingly supports both possibilities. The horseshoe crab expresses exceptionally clear circatidal rhythms and is thus a good choice for addressing this issue. Our results suggest the presence of two circalunidian clocks in horseshoe crabs: 1) When animals were given two tidal cues of different periods (24.8 and 24.2h), synchronization to both tides occurred. 2) In some animals these rhythms persisted in constant conditions in phase with previous tidal cues suggesting entrainment of two separate clocks. 3) Rarely, but significantly, two bouts of activity were expressed, each with different free running periods. 4) In other experiments, only one bout of activity/day was evident during either constant conditions or during tidal cycles; later under the same conditions, two bouts of activity/day could be observed. Taken together these results and others are consistent with the hypothesis that in this species locomotor activity is controlled by two circalunidian oscillators that are strongly coupled. In addition, since it is not uncommon to see only one bout of activity/day, decoupling of one of the oscillators from downstream locomotor centers may commonly occur, an outcome that could serve intertidal species well in areas where there is only one tide/day.
