Staying ahead of the game—plasticity in chorusing behavior allows males to remain attractive in different social environments

Abstract

The dynamic nature of many breeding aggregations, where the composition and attractiveness of a male’s competitors are ever changing, places extreme pressure on advertising males to remain competitive. In response to this challenge, males may adjust the properties of their calls or change when they signal relative to their nearest neighbors, which are likely their strongest competitors. We used two playback experiments—one simulating a conspecific environment and the other simulating a mixed-species environment—to test the hypothesis that males use social plasticity in signal features, signal timing, or both, to remain attractive. Further, we examined whether this plasticity is mediated by selective attention, through which males change calling behavior in response to the most relevant competitors, while disregarding less relevant rivals. We find that males change some temporal call features, but rely strongly on signal timing to remain attractive relative to rivals. Simultaneous assessment of both types of calling plasticity allowed us to makes sense of counterintuitive responses of male calling behavior that would otherwise appear non-adaptive. We further show that this plasticity is most pronounced in response to attractive/conspecific males. We discuss how sexual selection by female choice may influence the trade-off between call feature and call timing plasticity, as well as how competitive interactions on a local scale may affect the overall acoustic environment in the chorus. Males of group-signaling species face intense pressure to stand out from the crowd to attract mates—not only must they produce attractive signals, those signals must also be perceived clearly above the din. As signaling is a costly endeavor, it would be adaptive for males to recognize the relative attractiveness of their competitors and to adjust signaling behavior as the social environment changes. Using playback experiments, we show that male treefrogs modify call features and call timing in response to more attractive rivals. Our study also highlights that when studying chorusing species, the dual demands of producing attractive calls and placing them in attractive positions require simultaneous attention to both aspects of calling behavior. Only then is it possible to appreciate the potential trade-offs involved: males lengthening their call period when interacting with attractive rivals would appear maladaptive without the knowledge that this behavior results in reduced call overlap.