Quantitative studies on the elicitation of the electrodermal response by calls and synthetic acoustical stimuli in Rana Lessonae camerano, Rana R. Ridibunda pallas and the hybrid Rana “Esculenta” L. (Anura, Amphibia)

Abstract

The thresholds of the electrodermal response (EDR) were determined for the European water frogs Rana lessonae, Rana ridibunda ridibunda, and their hybrid, Rana “esculenta”. Both males and females were tested, during and outside the calling period. The stimuli used were the mating, territorial and release calls of all three phenotypes, as well as synthetic acoustical stimuli having the same impulse pattern but differing in frequency. The EDR could be elicited by all the calls tested, and by the synthetic acoustical stimuli at frequencies between 100 and 4000 Hz. Below ca. 1000 Hz the thresholds of the smaller Rana lessonae were higher than those of the bigger Rana ridibunda, while the relations were reversed above 1000 Hz. During the calling period the highest thresholds, in all three phenotypes, were those to the conspecific mating call. The synthetic stimulus at the dominant frequency of the mating call elicited the EDR only at sound pressures considerably higher than those of an effective synthetic stimulus at the dominant frequency of the territorial call. The thresholds to the territorial and release calls during the calling period were only slightly different from those at other times. Those to the mating call and to the synthetic stimulus at the dominant frequency of the mating call, however, were significantly lower than during the calling period. For each phenotype, the stimulus exhibiting the greatest seasonal fluctuation in threshold was the conspecific mating call.