Dynamic response of a cricadian pacemaker

Abstract

The stability of the Culex circadian oscillation in darkness was tested by perturbing it with bright light pulses. (1) In the absence of perturbation the overt circadian rhythm persists in darkness for at least 2 weeks (Fig. 5). (2) The circadian pacemaker, as perceived by the response to a standard phaseresetting signal, also follows a regular cycle in the absence of perturbation (Fig. 4). (3) Almost all light pulse perturbations quickly shift the phase of both overt rhythm and pacemaker, and the system resumes normal oscillation within 24 h (Figs. 6, 7, 8, and 9). (4) By contrast, perturbations driving the pacemaker near its phase singularity cause unpredictable phase shifts and/or disrupt individuals' overt rhythms for many cucles (Figs. 12, 13, and 14). Such pulses also sharply reduce the perceived amplitude of the pacemaker's oscillation (Figs. 10, 11, and 15). Most mosquitoes resume normal oscillation within a week but in some cases abnormalities persist for at least 2 weeks. The results re-emphasize the analogy between the circadian pacemaker and a simple limit cycle oscillator. The lasting anomalous behaviour of some mosquitoes after some pulses can either be explained by invoking a weakly unstable singularity, or simply treated as a minor, and perhaps revealing, deviation from prediction.