Relation of the Circadian System to the Photoperiodic Clock in Drosophila triauraria (Diptera: Drosophilidae) : An Approach from Analysis of Geographic Variation

Abstract

This paper investigated the relationship between the circadian system and photoperiodic time measurement in different geographic strains of Drosophila triauraria which enters reproductive diapause at short daylenggths. The critical daylength varied among the geographic strains, about 13 h in the ON (originated from Onuma, 42°N), 12 h in the OI (Oita, 33.2°°N) and 10 h in the YK (Yakushima, 30.3°N) strains at 15°C. All the strains exhibited a weak“circadian”oscillation pattern in diapause incidence on NANDA-HAMNER protocol. The dependence of photoperiodic time measurement on cycle lengths close to module τ was shown for the ON and OI strains by experiments using non-24 h light-dark cycles. Thus, no evidence was obtained for covariation between critical daylength and circadian oscillation pattern. The ON and OI strains showed similar patterns ofresponse in the night-interruption experiment, despite the one-hour difference in critical photoperiod.