Persistent Activity Rhythms in the Oyster

Abstract

Oysters were collected in New Haven harbor, shipped to Evanston, Illinois, and in the latter place maintained for 46 days in constant low illumination and constant temp. A continuous record of the opening and closing of the valves revealed, upon analysis, that these animals possessed persistent rhythms of primary solar, primary lunar or tidal and monthly frequencies. The form of the daily cycle was different during the first and second fortnights of a lunar period, but in every instance possessed three maxima, one in the early morning, another near noon, and a third in the evening. The tidal cycles for the first two weeks had maxima corresponding with the times of high tide in the site from which the oysters had been collected. An analysis of the data for the second two-week period showed that the times of maxima had shifted by three hours to occur at the times of lunar zenith and nadir in Evanston, Illinois, and these latter phase relationships persisted during the third and last two-week period of observation. There was no tendency for the amplitude of the rhythms to become reduced during the month and a half in constant conditions; on the contrary, they tended to increase slightly.