EFFECTS OF TEMPERATURE ON WEAK CIRCADIAN ECLOSION RHYTHMICITY IN CHYMOMYZA-COSTATA (DIPTERA, DROSOPHILIDAE)

The adult eclosion rhythms of two Japanese strains of Chymomyza costat a were studied in diel thermoperiods of different duration and at diff erent average temperatures, One of the strains had the 'wild-type' pho toperiodic larval diapause and the other was a mutant strain lacking t he photoperiodic response. At constant temperatures the wild-type stra in had weakly rhythmic eclosion in diel photoperiods while the mutant strain was arrhythmic, Free-running rhythms could scarcely be observed at all, The amplitude of the rhythm of both strains was much higher i n diel temperature cycles than in corresponding light-dark cycles, and generally higher in continuous darkness than in continuous light, Whe n the average temperature under entraining conditions was lowered, the rhythmicity increased and the median of the eclosion peak was displac ed to later hours in the entraining cycle. Both strains were rhythmic at the lowest temperatures, i.e. near 10 degrees C. At low temperature s the majority of the eclosions occurred during the high temperature p hase or light phase of the entraining cycle, Although the rhythm start ed well in the entraining temperature cycles, the subsequent free-runn ing rhythm in constant conditions lasted for only 2-3 days. We conclud ed that the exceptionally weak rhythmicity of eclosions and the relati ve importance of temperature cues are adaptive traits which make it po ssible for this northern species to respond directly to favourable but unpredictable changes in its environment. (C) 1997 Published by Elsev ier Science Ltd.