Type-II phase response dynamics facilitate synchronization in Photuris frontalis fireflies

The synchronization of many thousands of Photuris frontalis fireflies is a visually impressive spectacle naturally occurring in the southeastern United States. This is a rhythmically flashing species whose collective behavior results in continuous synchrony, resembling a silent metronome spreading throughout the darkened woods. To understand the oscillatory dynamics of individual fireflies within the collective, we performed a series of behavioral assays which introduced LED stimuli to isolated fireflies. Each assay measured the period of the firefly signal prior to and following exposure to the driving stimulus, as well as the phase of the driving signal with respect to the driven firefly and its effect on the induced periodic behavior. Through hundreds of such behavioral assays we construct a phase response curve (PRC) of Photuris frontalis oscillation behavior that reveals both excitatory and inhibitory effects, as these fireflies demonstrate flexible synchronization strategies akin to Type II neuronal oscillator networks. We explore these results through simulations of an integrate-and-fire model based on the PRC and nonlinear analysis of the fitted impulse function. This work provides a mechanistic link between microscopic phase responses and macroscopic synchronization, illuminating how collective rhythms emerge from individual dynamics.