MARSHALL, V.T.; SCHWARTZ, J.J.; GERHARDT, H.C.; University of Missouri-Columbia; Pace University; University of Missouri-Columbia: The influence of heterospecific acoustic interference on phonotaxis behavior in the gray treefrog Hyla versicolor

In a frog chorus, signalers and receivers face the problem of overlap between the advertisement calls of nearby neighbors. The influence of such overlap on the behavior of receivers is poorly understood, although acoustic interference has been suggested to proximally constrain the efficiency of communication, increase the difficulty for a receiver to find a mate and ultimately drive the evolution of signaling systems. In syntopic populations, males of the two sibling species of gray treefrogs (Hyla versicolor and H. chrysoscelis) form mixed-species choruses. We investigated how overlap between the signals of the two species influenced female phonotactic behavior and mate choice in Hyla versicolor. In two-speaker experiments, extensive overlap between the advertisement calls of the two species not only increased female response times, but also led them to make significant errors in their choice of stimulus (a significant proportion chose a speaker broadcasting H. chrysoscelis calls). With decreasing degrees of overlap, response times improved and error rates decreased. In general, these results predicted female behavior in a second set of experiments in which they were given a choice between overlapping and non-overlapping stimuli. Females preferred non-overlapping conspecific calls to those overlapped by H. chrysoscelis calls, and the intensity independence of this preference depended on the degree of overlap in the interfering alternative. The behavior of females suggests that H. chrysoscelis calls do not simply mask or degrade conspecific signal structure, but also influence where conspecific calls are localized by receivers.