Vol. 112, No. 3 June, 1957 THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY PERSISTENT TIDAL CYCLES OF SPONTANEOUS MOTOR ACTIVITY IN THE FIDDLER CRAB, UCA PUGNAX 1 MIRIAM F. BENNETT, JOAN SHRINER AND ROBERT A. BROWN Szveet Briar College, Siveet Briar, Virginia, Northwestern University, Evanston, Illinois, and the Marine Biological Laboratory, Woods Hole, Massachusetts Early in the present century, it was reported that a number of littoral organisms showed cycles of behavior which persisted under so-called constant laboratory con-ditions with tidal frequencies and with phases adaptively related to tidal events of the areas from which the organisms were collected (Gamble and Keeble, 1903, 1904 ; Bohn, 1904, 1906). Later, Compel (1937) found that several species of animals display tidal rhythms of Oo-consumption which also persist under constant labora-tory conditions. These reports were not very successful in convincing the majority of biologists of the reality of persistent tidal rhythmicity. However, during the past few years, a number of studies have again pointed out that many organic processes, e.g., color change, spontaneous activity, and Oo-consumption, in a rather wide vari-ety of plants and animals do indeed vary with primary lunar or tidal frequency under constant conditions. Rao (1954) found that the filtering rate of species of Mytilns was greatest at the times of high tides in the areas of collection when the mussels were maintained in the laboratory. This rhythm of behavior was clearly apparent day by day. However, many of the lunar or tidal cycles that have been described are apparent only by sta-tistical analyses of 15 or 29 days of continuous data (Brown, Freeland and Ralph, 1955 ; Brown, Webb, Bennett and Sandeen, 1955 ; Brown, Shriner and Ralph, 1956). The results of the work to be described demonstrate that the fiddler crab, Uca pugna.v, does have an overt rhythm of primary lunar frequency, a rhythm of spon-taneous motor activity. MATERIALS AND METHODS In both 1955 and 1956, males of the species Uca pugnax were used in these studies. The crabs were collected from Chapoquoit beach or Sippiwisset beach on the Buzzards Bay side of Cape Cod. Tidal events on these two beaches occur roughly 10 minutes later than they do at New York City. In the laboratory the animals were kept in white-enamelled pans in a small amount of sea water until they 1 These studies were aided by contracts between the Office of Naval Research, Department of Navy, and Northwestern University, NONR 122803. 267
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