Mechanisms and evolution of synchronous chorusing: emergent properties and adaptive functions in Neoconocephalus...

Synchronous interactions arise in various animal species that rhythmically broadcast acoustic, vibratory, and visual signals. These interactions are characterized by a coincidence in both rate and phase of the rhythms of neighboring signalers. Theory predicts several ways in which synchronized rhythms may specifically benefit the interacting signalers. However, synchrony may also arise as an emergent property, a default phenomenon that is neither preferred by conspecific receivers evaluating the signals nor advantageous to the signalers themselves. Here, we examine several well-studied cases of acoustic synchrony in Neoconocephalus katydids (Orthoptera: Tettigoniidae), a New World genus wherein males broadcast loud advertisement songs. We report that call synchrony found in N. spiza and N. nebrascensis results from two rather different mechanisms of rhythm adjustment. Moreover, synchrony in the former species appears to represent an incidental byproduct of signal competition between evenly matched males, whereas in the latter species synchrony functions as a specific adaptation in which cooperating males ensure that critical call features can be perceived by females. We discuss the separate evolutionary trajectories that may have led to similar outcomes, synchronous chorusing by advertising males, in these closely related species.