PERSISTENT DAILY AND TIDAL RHYTHMS OF COLOR CHANGE IN CALLINECTES SAPIDUS

Abstract

Immature specimens of Callinectes sapidus. collected in Lake Pontchartrain, La., were placed in a dark-room on evening of collection. Degree of melanophore pigment dispersion on their walking legs was determined on subsequent days. There was a diurnal rhythm of pigment migration; pigment was semidispersed by day and concentrated by night. Superimposed upon this diurnal rhythm was a tidal rhythm with a frequency of 12.4 hours. Latter rhythm, evidenced by a supplementary dispersion of melanin, occurred about 50 minutes later each day and was most pronounced when high or low tide was either in morning or late afternoon. At these times diurnal rhythm curve was skewed to left or right or was bimodal, depending upon exact times of tides. Phases of tidal rhythm bore a definite relationship to times of low and high tide in habitat. Callinectes were taken from a region exhibiting primarily diurnal tides but showed no difference between their rhythmical response to a low tide and a high tide which occurred at same hour on different days. Phases of diurnal and tidal rhythms with respect to one another were unaltered on days when usually duirnal tidal cycle in habitat became semidiurnal.