PHASE DIFFERENCE IN THE TIDAL RHYTHMS OF COLOR CHANGE OF TWO SPECIES OF FIDDLER CRAB

Publisher Website
Google Scholar
Abstract
Specimens of fiddler crabs, Uca pugilator and U. speciosa, were collected at Ocean Springs, Miss., anc maintained in constant darkness in laboratory. Pigment in melanophores of fiddler crabs showed a persistent tidal rhythm with a frequency of 12.4 hrs. Nature of tidal rhythms of both spp. was similar to tidal rhythms previously reported for fiddler crab U. pugnax and blue crab, Callinectes sapidus. No detectable difference in character of pigment migration was apparent at times of low and high tide which occur 12.4 hrs. apart where these 2 spp. of Uca collected. Tidal rhythm of U. speciosa was 6 days in advance of tidal rhythm of U. pugilator. Difference is equivalent to 4.9 hrs. in tidal cycle. Hypothesis presented to explain this tidal difference. Difference in habitat of 2 spp. of Uca on same beach, width of beach, and time required for water to recede from burrows of Uca speciosa to burrows of U. pugilator which live at a lower level of beach are factors which have been considered in formulating hypothesis. A semilunar rhythm of amplitude of daily dispersion of pigment in melanophores of both spp. was found. Possible adaptive significance of phase difference of tidal "rhythms of 2 spp. discussed.