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

Cricket frogs (Acris crepitans) occupy a variety of acousticallydifferent habitats ranging from pine forest to open grassland.There is geographic variation in their calls and the tuningof their basilar papilla (BP) correlated with habitat. Here,we characterize the spectral content of environmental noisefrom two habitats, one a pine forest (Stengl) and one a grassland(Gill) habitat. We then used rounded exponential filter functionsbased on the mean tuning of auditory fibers in Stengl and Gillfemales to model the BP tuning characteristics of an averagefemale from the two cricket frog populations occupying thosehabitats to compare their ability to filter out environmentalnoise. Noise recordings were made at both sites from 1800 to2400 h on multiple nights throughout a breeding season (Marchthrough early August). Noise spectra were similar at both sites.Cross-correlation analyses of the sampled noise indicated thatnoise spectra were consistent throughout the night and variedlittle over the season other than during the month of May. Themodel auditory filter simulating an average Stengl female wassignificantly better than one simulating an average Gill femaleat filtering environmental noise at both sites. Previous workhad shown that cricket frog calls suffered greater attenuationand degradation in the Stengl site than the Gill site but thatthe male calls from Stengl frogs suffered less attenuation andless degradation than Gill calls during transmission throughboth habitats. These new results demonstrate that frogs fromthe more acoustically challenging Stengl habitat have enhancedboth the sender and receiver portions of their communicationsystem, evolving calls that transmit better and auditory filtersthat better eliminate noise.