AJP - Regulatory, Integrative and Comparative Physiology, Vol 241, Issue 5 322-R329, Copyright © 1981 by American Physiological Society
A critical examination of the dual system theory in Ostrinia nubilalis
S. D. Skopik, M. Takeda and C. W. Holyoke
Beck's dual system theory (DST) is examined theoretically and
experimentally by investigating the oviposition rhythm of Ostrinia
nubilalis and its entrainment by light cycles. Several well-known circadian
phenomena are not accounted for by the DST. 1) It does not generate
transient cycles when light pulses fall during the advance portion of the
circadian cycle. This is also reflected in DST-predicted phase-response
curves (PRC's) for both Drosophila pseudoobscura and O. nubilalis.
Steady-state phase advances are predicted to occur on day 1 after the light
pulses by the DST, not several cycles later as has been observed in many
cases. 2) It does not account for the observation that the magnitude of a
phase shift (delta phi) is often a function of pulse duration of both
delays and advances. The DST predicts the same + delta phi, for example,
for a 0.5-h and a 6.0-h light pulse beginning 5.0 h after dusk. 3) The DST
does not accurately predict steady-state phase relationships between the
light cycle and the gating oscillation (P-system) in non-24-h light cycles.
4) The driver (S-system) is given the property of being temperature
sensitive whereas the driven rhythm (P-system) is temperature compensated.
This is contrary to accumulated data suggesting that the circadian
pacemaker is temperature compensated.
