Physiological basis of convergent evolution in animal communication systems.

To humans, the diverse array of display behaviors that animals use for communication can easily seem peculiar or bizarre. While ample research delves into the evolutionary principles that shape these signals' effectiveness, little attention is paid to evolutionary patterning of signal design across taxa, particularly when it comes to the potential convergent evolution of many elaborate behavioral displays. By taking a mechanistic perspective, we explore the physiological and neurobiological mechanisms that likely influence the evolution of communication signals, emphasizing the utilization of pre-existing structures over novel adaptations. Central to this investigation are the concepts of perceptual bias and ritualization, which we propose contribute to the convergence of elaborate display designs across species. Perceptual bias explains a phenomenon where pre-existing perceptual systems of receivers, used for innate behaviors such as food and predator recognition, select for certain traits of a communication signal from a signaler. Ritualization occurs when traits with no functional role in communication are co-opted through selection and transformed into a new communicative signal. Importantly, susceptibility for ritualization can be brought about through physiological modifications that occurred early in evolutionary time. In this way, perceptual bias can be a selective force that causes the co-option of non-communicative traits into a new communication signal through ritualization involving pre-existing modifications to physiological systems. If the perceptual bias, non-communicative signal, and physiological modifications that increase susceptibility to ritualization are highly conserved, then we may see the convergent evolution of the new communication signal with unrelated taxa facing similar sensory constraints. We explore this idea here using the foot-flagging frog system as a theoretical case study.