Entrainment of the Circadian Clock Gating Prothoracicotropic Hormone (PTTH) Secretion in the Swallowtail, Papilio xuthus L. (Lepidoptera : Papilionidae) : I. Complete Photoperiods

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In 4th instar Papilio xuthus larvae, PTTH was secreted in a rhythmic manner even in continuous darkness (DD) following both 8L-16D and 16L-8D. The PTTH secretion rhythm was phase-shifted by exposing larvae to a light pulse (1 hr) in DD. The phase-shift produced in the rhythm represents a typical phase-response. The onset, acrophase and offset of the PTTH-secretion occurred parallel to the mid-points of light (or dark) periods. The rhythm free-ran in continuous darkness (DD) following various LD cycles in which light periods were changed at 2 hr intervals. Coefficients of regression lines (RC-values) for the onset, acrophase and offset of PTTH-secretion were calculated against the lights-on in free-running rhythms were examined in DD and LL (continuous light), and were far smaller in the latter. The RC-values, however, for the 3 phase reference points (∅r's) of PTTH-secretion rhythm increased from one ∅r to the next in DD following LD cycles. The results suggest that PTTH secretion in P. xuthus is gated by a circadian clock which is set twice a day, at dawn and dusk. At dawn the circadian clock may be reset at CT 0 : 00,and again set at dusk to give the same time (CT 18 : 00) amid the dark period of LD cycles.
日本応用動物昆虫学会の論文
1990-02-25