Effects of Temperature on Weak Circadian Eclosion Rhythmicity in Chymomyza costata (Diptera: Drosophilidae)

The adult eclosion rhythms of two Japanese strains of Chymomyza costata were studied in diel thermoperiods of different duration and at different average temperatures. One of the strains had the 'wild-type' photoperiodic larval diapause and the other was a mutant strain lacking the photoperiodic response. At constant temperatures the wild-type strain 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 in diel temperature cycles than in corresponding light-dark cycles, and generally higher in continuous darkness than in continuous light. When the average temperature under entraining conditions was lowered, the rhythmicity increased and the median of the eclosion peak was displaced to later hours in the entraining cycle. Both strains were rhythmic at the lowest temperatures, i.e. near 10 degrees C. At low temperatures the majority of the eclosions occurred during the high temperature phase or light phase of the entraining cycle. Although the rhythm started well in the entraining temperature cycles, the subsequent free-running rhythm in constant conditions lasted for only 2-3 days. We concluded that the exceptionally weak rhythmicity of eclosions and the relative importance of temperature cues are adaptive traits which make it possible for this northern species to respond directly to favourable but unpredictable changes in its environment. Copyright 1997 Published by Elsevier Science Ltd. All rights reserved