Evidence of escalated aggressive calling behavior in a male agonistic interaction of the reticulated leaf frog Pithecopus ayeaye

Vocalizations are the most prominent signals in the communication of anuran amphibians. Frog calls can serve different roles depending on the social context. There are three categories of vocal signals (calls) based on social context. One of these is the aggressive call, which generally mediates interactions between conspecific males and conveys information about the level of aggression. In this study, we describe fighting calls elicited during physical combat between two males of Pithecopus ayeaye. We also analyzed aggressive calls not associated with physical combat, which were emitted by resident males from an established calling site toward approaching males, and discussed the variation related to different levels of aggression. The fighting call consists of one multi-pulsed note with an increment in sound amplitude throughout the note and amplitude peak by 96% of note duration. In general, fighting calls and aggressive calls have the same temporal envelope and spectral features. However, fighting calls exhibit a greater number of pulses, a higher pulse repetition rate, and a longer duration. The differences between aggressive calls of P. ayeaye produced in distinct contexts could indicate a graded signaling system in the aggressive calling behavior of the species. Our data match the pattern of escalated aggressive behavior occurring in other vocal anurans by modulating spectral and/or temporal features of their calls.