Rhythms of activity and oxygen consumption in the common pond clam, Ligumia subrostrata (Say)

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Abstract
Diurnal rhythms were found in the unionid clam L. subrostrata for valve activity and O2 consumption. Valve closures and valve gape were measured as indices of valve activity. Recordings were made after the animals were entrained to each of 3 photoperiods: 12 h light (L):12 h dark (D), 16L:8D, and 24L. Statistically significant (P < 0.01) rhythms of activity were found in 12L:12D and 16L:8D photoperiods with high activity occurring during the dark phase. The onset of darkness was indicated as the entraining factor. No rhythm of valve activity was found in 24L. Flow-through respirometry of individual clams was used to determine if O2 consumption paralleled activity rhythms. Rhythms of O2 consumption were present in all 3 photoperiods with a change in light rather than the onset of darkness as the entraining factor. The activity rhythm was exogenous, whereas the O2 consumption rhythm was an endogenous rhythm. Overall levels of activity and O2 consumption were highest in the 16L:8D regimen and depressed in constant light.