Environmental influences on acoustic communication in frogs

Abstract

Many species of animals, including man, face the formidable task of communicating in naturally noisy environments. The effects of noise on both the calling behavior of frogs and the temporal, and spectral filtering ability of the amphibian auditory pathway are discussed. Moreover, the role of spectral, temporal, and spatial separation in minimizing background noise masking will be examined. Behavioral evidence is presented suggesting that environmental noise may act as a strong selective force in sculpting the communication systems of two species of Old World frogs. One torrent frog (Odorrana tormota) calls frequently from vegetation along fast-flowing mountain streams in Central China. These streams produce high-level, broadband noise spanning the human hearing spectrum. In addition to the high-pitched audible components, the males' calls contain prominent ultrasonic harmonics. Another frog, Huia cavitympanum, lives in a very similar habitat in Borneo. Unlike O. tormota, Huia can modulate its call spectrum to produce purely ultrasonic calls. It is thought that the upward shift of the call frequencies and the upper limit of sensitivity of both O. tormota and H. cavitympanum are responses to the selection pressures from their noisy habitats. [Work supported by NIDCD DC-00222, Paul S. Veneklasen Research Foundation, UCLA Academic Senate (3501).]