An Analysis of the Mechanisms of Mating Call Discrimination in the Frogs Hyla regilla and H. cadaverina

Abstract

Evaluation of the role of frequency spectrum, duration, temporal pattern of pulses and pulse form components in call discrimination behavior of H. regilla and H. cadaverina showed that pulse repetition rate is the only necessary component for effective discrimination. In each species the frequency of best hearing matches the dominant frequency of the call which optimizes detection of the calls but does not effect discrimination. MANY species of Anura maintain genetic integrity through ethological premating reproductive isolating mechanisms. This is largely accomplished by the ability of females to discriminate between mating calls of homospecific males and those of other sympatric species. Thus, encoding of species specific information in such calls and its analysis by the auditory system is essential. Straughan (1973) indicated that call discrimination by females was well established in some groups of frogs (i.e. Hylidae), but that the mechanisms of discriminatory behavior were not fully understood. Evidence from studies on neurophysiology and evoked vocal behavior of males of Rana catesbeiana indicated that the important component of the call was the dual peak power spectrum which was matched by a dual band pass frequency filter in the ear involving the amphibian and basillar papillae. Simultaneous stimulation of both papillae produced neurophysiological perception to correct vocal stimulus (Capranica, 1965). However, trials of female discrimination (Loftus-Hills and Littlejohn, 1971) indicated that the most important component for Litoria ewingi and L. verreauxi was pulse repetition rate. They argued that temporal components other than pulse repetition could not be encoded species specific information but they did not deal experimentally with each component. Generalization from these results are thus restricted to calls of the same basic structure.