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Induction and Inhibition of Diapause by the Same Photoperiod: Experimental Evidence for a "Double Circadian Oscillator Clock"

Department of Animal Ecology, University of Bielefeld, Morgenbreede 45, D-33615 Bielefeld, Germanyhubert.spieth{at}uni-bielefeld.de

Fangsen Xue

Institute of Entomology, Jiangxi Agricultural University, Nanchang, China

Katharina Strau

Department of Animal Ecology, University of Bielefeld, Bielefeld, Germany

On the southern Iberian Peninsula, the seasonal life history of the large white butterfly, Pieris brassicae, comprises 2 different photoperiodically induced developmental arrests: a hibernation diapause at photophases < 11 h and an estivation diapause at photophases > 14 h. At intermediate photophases (12 h to 13 h), the butterfly responds with a nondiapause. Combined with the experimental setup to determine photosensitivity in insects, the different photoperiodic responses at long-, intermediate-, and short-night conditions were examined to gain more insight into the time measurement mechanism in P. brassicae. The study reveals evidence for a "double circadian oscillator clock" mechanism that is based on 2 submechanisms, a "short-night determining system" and a separate "long-night determining system." This conclusion was drawn from the facts that an LD 9:15 long-night induces a hibernation diapause but inhibits an estivation diapause and, conversely, that an LD 16:8 short-night inhibits a hibernation diapause but induces an estivation diapause. This opposite effect of the same photoperiod supports the argument for the existence of 2 independent targets for light-dark cycles, interpreted as 2 antagonistic time measurement systems. The existence and independence of 2 systems was further shown by differences in long-night versus short-night responses regarding photosensitivity, temperature dependence, and heritable factors. The long-night measurement system is most effective in the 5th larval stage, is highly affected by temperature, and is easy to manipulate by selective inbreeding. The short-night measurement system is most effective in the 4th larval stage, is largely temperature compensated, and is not affected by experimental manipulation of the longnight measurement system.

Key Words: clock mechanism • time measurement • photosensitivity • Pieris brassicae • photoperiodic response • estivation • hibernation

Journal of Biological Rhythms, Vol. 19, No. 6, 483-492 (2004)
DOI: 10.1177/0748730404270388


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