Evolutionary and neurobiological implications of selective phonotaxis in the green treefrog, Hyla cinerea

Abstract

An extensive series of two-speaker and four-speaker playback experiments using synthetic advertisement calls identified acoustic criteria that may be used by females of the green treefrog, Hyla cinerea, in choosing a mate. At a sound pressure level (SPL) of 75 dB (decibels re 20 μPa) females preferred signals which had a low-frequency spectral peak in the range 0·8–1·0 kHz and a high-frequency spectral peak in the range 2·4–3·6 kHz. Some frequency preferences were reduced or abolished by changing the absolute or relative SPLs of the experimental stimuli. Frequency selectivity in the low-frequency range decreased with playback level; selectivity in the high-frequency range increased with playback level. Females were less selective with respect to variation of the low-frequency peak in four-speaker experiments than in two-speaker experiments. Frequency preferences were independent of female body size. Females responded selectively to signals that differed in call duration and relative SPL; some preferences depended on absolute SPL. Females preferred signals with higher (15–100%) than average repetition rates to those with average rates, but did not respond at all to calls repeated at about four times the normal rate. These results are discussed in terms of current knowledge on auditory physiology and recent data on patterns of call variation and mating success among male green treefrogs.