Meeting Abstract

P2.11  Wednesday, Jan. 5  Can frogs turn it up to 11? A test of voice amplitude regulation in Cope’s gray treefrog LOVE, E.K.*; BEE, M.A.; University of Minnesota, Twin Cities; University of Minnesota, Twin Cities love0251@umn.edu

Animals that communicate acoustically must cope with problems posed by environmental background noise. One method for doing so is to increase signal amplitude as noise amplitude increases, a phenomenon known as the Lombard Effect. Voice amplitude regulation is prevalent among many birds and mammals, including humans, and has been suggested as a general vertebrate mechanism for coping with background noise. However, there is limited support for this evolutionary hypothesis due to a lack of studies of animals other than birds and mammals. We tested the hypothesis that male Cope’s gray treefrogs (Hyla chrysoscelis) increase the amplitude of their advertisement calls in response to increasing levels of noise simulating a breeding chorus. We recorded spontaneously produced calls in both quiet and in the presence of noise broadcast at sound pressure levels between 40 and 70 dB. Increases in noise level induced predictable changes in call duration and call rate, but failed to induce changes in call amplitude. Thus, our results do not support the hypothesis that noise-dependent voice amplitude regulation is a general vertebrate mechanism. Instead, we suggest that strong sexual selection and competition for mates favors males that signal as loudly as possible all the time.