Behavioral context shapes vocal sequences in two anuran species with different repertoire sizes

Abstract

Acoustic signals in animals serve to convey context-dependent information to receivers. Birds and mammals combine diverse sounds into complex sequences to communicate, but these sequences largely remain understudied in other taxa. Anuran vocalizations are a prominent feature of their life history, and function in defense of territories and to attract mates. However, despite the spectacular diversity of anurans in tropical regions of the world, vocal diversity and communication strategies remain relatively poorly studied. Specifically, studies of vocal sequences and context-dependent vocal patterns in frogs remain few. Here, we investigated the context-dependent vocal repertoire and the use of vocal sequences by two anuran species belonging to different lineages, both endemic to the hyper-diverse Western Ghats of India. By recording vocal sequences both when frogs were alone and in the presence of a territorial rival, we present evidence that both species modify their vocal repertoire according to context. Specifically, one species appends notes to generate more complex sequences, whereas the other shifts to different note types, resulting in different sequences for different contexts. Thus, despite differences in repertoire size, both frog species are capable of adjusting the temporal sequence of vocalizations to communicate in different contexts. This study highlights the need for further studies of insular frogs, to understand how diversification across these continental islands has influenced the evolution of vocal repertoires, vocal sequence patterns and communication systems. Lay SummaryAnimals employ complex sequences of acoustic signals to communicate in diverse behavioral contexts. Here, we demonstrate that two frog species with different vocal repertoires both modify the sequence of note emissions in the presence of a territorial rival. These patterns demonstrate that anurans are capable of complex shifts in the patterns of their vocalization, to communicate different messages to different receivers. Our findings demonstrate the value of studying behavioral diversity in tropical regions.