Evidence of two-clock control of endogenous rhythm in the Washington clam, Saxidomus purpuratus

Abstract

The oxygen consumption rates of sublittoral-dwelling Washington clams, Saxidomus purpuratus (Bivalvia: Veneridae), were determined using an automatic intermittent-flow-respirometer under constant darkness and temperature. Freshly collected clams displayed a bimodal rhythm for the first 7-9 days, and a unimodal rhythm after holding in constant conditions (CC). Therefore, clams collected from the sublittoral zone likely exhibit responses that correspond to the tides in their original environment for several days, and then shift to an endogenous unimodal (circadian) rhythm when kept under CC. This study may suggest that Washington clams possess two independent clocks that can change the rhythm of endogenous oxygen consumption from bimodal to unimodal under CC.