Environmental factors influencing call propagation in Pithecopus nordestinus: testing the Acoustic Adaptation Hypothesis

The acoustic adaptation hypothesis (AAH) states that the acoustic signal of a species must propagate better in its native habitat. Studies have shown that certain anuran species modify acoustic parameters according to the environment where they are calling. However, these studies did not verify if these modifications improved the call’s transmission. We investigated whether advertisement calls of Pithecopus nordestinus (Phyllomedusidade) propagated more efficiently in two habitats where the species has evolved over generations (Caatinga and Atlantic Forest) and, according to the predictions of the AAH, whether specific acoustic parameters (number of pulses, interval between pulses and dominant frequency) maximise transmission. We measured the efficiency of the transmitted signal (natural and synthesised calls) in different environments. Our results showed that natural calls from Caatinga habitats were less degraded. We found that synthetised calls with shorter intervals between pulses propagated just as well in both the Caatinga and the Atlantic Forests. Finally, the dominant frequency was influenced by the propagation environment and, synthetised calls with higher frequencies showed less degradation when propagated in the Caatinga. Our results indicate that not all differences found in the acoustic parameters of anuran calls in distinct environments can be attributed to the acoustic adaptation hypothesis.