Synchronous Flashing in Southeast Asian Fireflies
Biology 342 Fall 08 - Matt Hagen and Laurel Oldach
What is an Oscillator?
Neural oscillation is periodic rhythmic activation of a neuron. This activity can be demonstrated in fireflies by electrically stimulating certain brain regions: electrical input elicits rhythmic behavior, even if they inputs are arrhythmic. A neural pacemaker is a network of oscillating neurons that controls some rhythmic behavior by cycling through levels of activity. In a flash cycle the "level of the pacemaker gradually ascends, then descends to its lowest (basal) level and initiates another cycle. (Greenfield 1994).
How do oscillators interact?: Entrainment and inhibitory resetting
Two males at the proper distance from each other will begin to flash in synchrony within one flash cycle, and deviate from one another by less than sixteen milliseconds per 560 millisecond cycle (Buck and Buck 1978). Females do not synchronize with males but rather enter a regular pattern of flashes timed slightly after the synchronized males'.
Synchrony relies on entrainment, the re-adjusting of one male's neural oscillator to match the flash pattern of another male. When two males are introduced, whichever male flashes first maintains his characteristic pattern while the latter male adopts the pattern of the former, maintaining it even when the first male is no longer within view (Buck 1988). This influence of one male's flash on another's pacemaker cycle is called inhibitory resetting. See the figure below.
Figure1: Inhibitory resetting. Thick lines above oscillator levels show focal male's flashes (occuring slightly after oscillator peak due to effector delay). Light lines below show external stimuli. If interfering signal occurs during ascent (first T' cycle), oscillator level drops and restarts cycle, delaying flashing to avoid an unattractive later-flash. If interfering signal occurs during descent, current flash is unaffected but ascent to trigger is more rapid. (Credit: Greenfield '96)