NORTH SOUTH DIFFERENCES IN CIRCADIAN ECLOSION RHYTHM IN EUROPEAN POPULATIONS OF DROSOPHILA-SUBOBSCURA

The circadian pupal eclosion rhythm was studied in 12 strains of Drosophila subobscura originating from two regions: Scandinavia (56-63-degrees-N), and the Canary Islands (28-degrees-N), In most parameters of the rhythm, ample variability was found both within and between the regions. Among the strains the phase of the eclosion median in an entraining diel light-dark cycle varied by 8.1 h, and the period of the free-running rhythm (tau) 2.2 h. In the comparison between the two regions, the Scandinavian entrained rhythm had on average a 2.8 h earlier phase, tau was 0.9 h shorter, and the amplitude of the rhythm was lower. Of the rhythm parameters, early phase was correlated with short tau (r = 0.76), and the amplitude of the entrained rhythm was correlated with the amplitude of the free-running rhythm (r = 0.98). In addition to the geographical variation, a putative arhythmic recessive autosomal mutant was found to segregate in one Scandinavian strain. The lack of photoperiodic adult diapause was confirmed in D. subobscura. The results show that the circadian eclosion rhythm in a non-photoperiodic species can vary latitudinally in a fashion similar to that of photoperiodic species.