How cricket frog females deal with a noisy world: habitat-related differences in auditory tuning

Abstract

Cricket frogs (Acris crepitans) occupy a variety of acoustically different habitats ranging from pine forest to open grassland. There is geographic variation in their calls and the tuning of their basilar papilla (BP) correlated with habitat. Here, we characterize the spectral content of environmental noise from two habitats, one a pine forest (Stengl) and one a grassland (Gill) habitat. We then used rounded exponential filter functions based on the mean tuning of auditory fibers in Stengl and Gill females to model the BP tuning characteristics of an average female from the two cricket frog populations occupying those habitats to compare their ability to filter out environmental noise. Noise recordings were made at both sites from 1800 to 2400 h on multiple nights throughout a breeding season (March through early August). Noise spectra were similar at both sites. Cross-correlation analyses of the sampled noise indicated that noise spectra were consistent throughout the night and varied little over the season other than during the month of May. The model auditory filter simulating an average Stengl female was significantly better than one simulating an average Gill female at filtering environmental noise at both sites. Previous work had shown that cricket frog calls suffered greater attenuation and degradation in the Stengl site than the Gill site but that the male calls from Stengl frogs suffered less attenuation and less degradation than Gill calls during transmission through both habitats. These new results demonstrate that frogs from the more acoustically challenging Stengl habitat have enhanced both the sender and receiver portions of their communication system, evolving calls that transmit better and auditory filters that better eliminate noise.