Abstract

The present study investigated 1) whether the luminous conditions of external LD cycles affect the synchrony of heart rate (HR) and scaphognathite beating rate (SB) daily rhythms and 2) whether both rhythms depend on the same circadian oscillator. Five groups were submitted to different cycles of 24h light conditions over three or more days: 1) control, LD 12:12 low irradiance 2) experiment 1, LD 12:12 high irradiance 3) experiment 2, LD 20:4 low irradiance, 4) experiment 3, 20:4 high irradiance, 5) experiment 4, 24 DD. Heart rate recorded by electrophysiological conventional methods as well as SB recorded by impedance methods were calculated for each hour. The data were statistically analysed. Results showed that under constant darkness, the crayfish’s HR and SB rhythms run freely with periods of ?= 22.6 and ?= 24.1 h respectively. Both rhythms are able to synchronize to LD 12:12 low and high irradiance as well as LD 20:4 low irradiance, with a similar value (?= 24 h) and a high degree of synchrony. However, LD 20:4 as well as darkness seem to produce the uncoupling of both rhythms, originating the asynchrony of both functions. These results indicate the presence of two different oscillators for the heart and ventilation rate.

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