Control of flashing in fireflies

Summary

Males of the fireflyPteroptyx cribellata of Papua New Guinea luminesce spontaneously in two principal modes: a regular one-per-second display flash (Fig. 1 A) and an irregular flicker of 3–10 peaks per second (Fig. 1B). In free run rhythmic display flashing by intact, restrained individuals, serial correlation analysis of interflash duration in successive cycles indicates that the variability of the brain-to-lantern excitation delay is negligible in comparison with the variability of the endogenous timing process (Figs. 6, 7). It is therefore possible to use the duration of the flash-to-flash interval of the intact firefly as a measure of endogenous pacemaker timing behavior. It is deduced that the cycling of the pacemaker is continuous, does not require that the animal see his own flash or even that he flash (Fig. 2 A), shows intercycle independence (Fig. 5) and may phase-shift its rhythm spontaneously upon occasion (Fig. 2C). Pacemaker period is normally distributed (Fig. 3), is not correlated with flash intensity, and appears to shorten slightly if a flash is skipped (Table 3). The occurrence of spontaneous flash skipping is taken to indicate that the timing process that measures pacemaker period can cycle independently of its usual triggering of the flash-excitation message to the lantern.