Control of flashing in fireflies

SummaryThe restrained male of the fireflyPteroptyx cribellata of Papua New Guinea responds to exogenous light signals with a latency of about one second, which equals the period of the natural spontaneous rhythm of flashing and includes about 800 ms of central nervous delay. The response is cycle-by-cycle and all-or-none and the duration of the response time is independent of the phasing of the driver in relation to the free run rhythm (Figs. 1, 2). The firefly can be entrained to rhythms over a period range of 800 ms to 1,600 ms, during which it leads or lags the concurrent signal by an amount equal to the difference between the driving period and the animal's period (Figs. 3, 4). The phase-response line is nearly straight and is inclined 45 ° (Figs. 2, 5). Normally an exogenous signal dictates interflash timing but occasionally may fail to entrain the firefly (Figs. 7B, E) or may fail to evoke a flash (Figs. 7F, G). Persistence of endogenous control of timing period duration even during driving is occasionally seen as spontaneous drift in response time (Fig. 9). It is proposed that during entrainment each exogenous signal resets the pacemaker immediately to the start of its endogenous cycle, from which point it then begins a new series of free run periods. Thus each flash is timed in relation to the signal of the preceding cycle (Fig. 3). We devised a model of the endogenous timing cycle which fits the empirical data and achieves entrainment by a single mechanism involving phase advance or delay rather than change in actual rate of endogenous timing (Fig. 12). The proposed mechanism by which single males entrain to light signals seems compatible also with the mass synchronous flashing which is the characteristic behavior of field congregations.