PERSISTENT DAILY AND TIDAL RHYTHMS OF COLOR CHANGE IN CALLINECTES SAPIDUS

Abstract

1. The pigment in the melanophores of Callinectes sapidus displays an endogenous diurnal rhythm with a frequency of 24.0 hours. The pigment is in the dispersed state during the day and in the concentrated state at night.2. The amplitude of the diurnal rhythm neither increases nor decreases under constant laboratory conditions.3. Superimposed upon the diurnal rhythm is a tidal rhythm with a frenquency of 12.4 hours. This rhythm is manifested by a supplementary dispersion of the melanin which occurs about fifty minutes later each day.4. The tidal rhythm is most evident when the low or high tide is either in the morning or late afternoon. When either a low tide or a high tide occurs at these times, the diurnal rhythm curve is skewed to the left or right or tends to be bimodal, depending upon the times of high and low tides. There is no difference of response to low and high tides.5. The tidal rhythm of Callinectes maintained under constant laboratory condititions has its phases bearing a definite relationship to the times of low tide and high tide in the native habitat of the crabs.6. The Callinectes continue to exhibit their response to tides spaced 12.4 hours apart even on days that the usually diurnal tidal cycle of their original habitat becomes semidiurnal.7. Callinectes also exhibits a semilunar rhythm. Only once every 14.8 days are the diurnal and tidal rhythms in the same phases relative to one another.