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The Effect of Photoperiod and Light Irradiance on the Antioxidant Circadian System of Two Species of Crayfish from Different Latitudes: Procambarus clarkii and P. digueti ¶

This work was carried out to study the antioxidant circadian system of two species of crayfish of different latitude origin. We investigated ( 1 ) whether both species possess glutathione circadian rhythms and ( 2 ) whether both species' rhythms differ in their ability to synchronize to 24 h cycles. Two batches of Procambarus clarkii and P. digueti were kept in ( 1 ) light–dark (LD) 12:12 low irradiance (LI) cycles and then exposed to ( 2 ) 72 h of complete darkness, ( 3 ) LD 12:12 high irradiance (HI), ( 4 ) LD 20:4 LI and ( 5 ) LD 20:4 HI for 2 weeks. The midgut and hemolymph were sampled and reduced and oxidized glutathione as well as glutathione reductase and glutathione peroxidase were assayed. Cosinor and analysis of variance revealed differences between both species. Procambarus clarkii robust antioxidant circadian rhythms are able to entrain to all conditions resetting to lights on or off. However, the P. digueti weak circadian glutathione system did not entrain to the LD cycles, showing a random distribution of phases. In this species, LD 12:12 and 20:4 HI evidenced significant daily rhythms indicating a damped circadian antioxidative system that is enhanced by the effect of light. This suggests that each species' photoperiodic history determines the adaptive abilities of the circadian antioxidative mechanisms.