Cut through the noise: vocal signals and auditory processing vary along an urbanization gradient in Pacific treefrogs

From dense assemblages of vocalizing organisms in neotropical rainforests, to fast-flowing streams and waterfalls in the Old World, Peter Narins' work has been instrumental to our understanding of how animals, particularly frogs, communicate in noisy environments. With increasing levels of human-generated noise, there has been an explosion of studies on how vocal signals and signaling behaviors change in urban soundscapes. Surprisingly, we know little about changes in sensory-processing mechanisms of receivers. We asked whether vocal signals, hearing sensitivity, and the ability to extract signals from noise of Pacific treefrogs (Pseudacris regilla) vary in ways that facilitate communication among sites with different levels of urbanization and noise. We show that males from sites with high levels of urbanization and noise produce calls at higher rates and lower frequencies. Auditory brainstem responses obtained in the presence and absence of noise reveal that, at frequencies present in the vocalizations, subjects from urbanized and noisy sites are less sensitive and experience reduced masking. Our results suggest that lower auditory sensitivity may function as a gain-reduction mechanism that improves the signal-to-noise ratio in sites with high levels of ambient noise. We discuss our results considering Narins' contributions to anuran auditory neuroethology.