TIME CUES FOR SEMILUNAR REPRODUCTION RHYTHMS IN EUROPEAN POPULATIONS OFCLUNIO MARINUS. II. THE INFLUENCE OF TIDAL TEMPERATURE CYCLES

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Abstract
Breeding experiments with the intertidal midge Clunio demonstrate that tidal temperature cycles combined with the 24 h light-dark cycle can act as time cues controlling the semilunar (lunar-semi-monthly) timing mechanism of the animals, regulating the semilunar emergence rhythm of the population. The 2 environmental cycles are in identical phase relationships every 15 days. Two types of temperature cycles were examined, sinusoidal fluctuations and short term pulses of 1.5 h (3.degree.-5.degree.C amplitude and 12.4 h period each). Comparing the entrained semilunar rhythms in terms of phase relationship to the time cues, the end of the warming interval seems to be the decisive parameter of the tidal temperature changes. The combined exposure to tidal temperature cycles and tidal cycles of mechanical disturbances of the water (an additional time cue in the populations examined) resulted in the correct semilunar synchronization when the temperature rises and the mechanical disturbances alternated as in a natural tidal cycle. The results from 3 stocks representing different geographical races are discussed in relation to the amplitude of tidal temperature changes in nature, to weak and strong influences of the time cues, to their perception and to the phase relationship between rhythms and time cues in the experiments and in nature.