Distress calls of two species of Pithecopus (Anura, hylidae) in Northeastern Brazil

Bioacoustics is essential to understand patterns of vocalization in anuran amphibians, including their advertisement, aggressive, and distress calls. Aggressive and distress calls occur when the individuals are threatened and present a strong phylogenetic signal, being potential taxonomic markers, especially for cryptic species. The genus Pithecopus includes 12 species of arboreal frogs, including the cryptic species P. nordestinus and P. gonzagai, two sympatric species that can be differentiated based on genetic, morphological, and acoustic features. This study describes and compares the distress calls of P. gonzagai and P. nordestinus, analyzing acoustic differences and the relationship with their advertisement call. We conducted field work at the Tapacurá Ecological Station, Pernambuco, Brazil, where the distress calls of three males of P. gonzagai were recorded. We compared with data on P. nordestinus, obtained from the Fonoteca Netotropical Jacques Vielliard. The results show that distress calls are longer, with higher frequency, and are more complex than advertisement calls, for both species. Moreover, there is a marked contrast for both calls between the two species, especially when considering distress call duration, with P. nordestinus emitting longer calls. Distress calls are still an understudied type of vocalization, despite being observed in many species. These results suggest that both ecological and evolutionary factors may have a role in shaping the vocalization of anurans, reinforcing the importance of bioacoustics for the systematics and conservation of Neotropical amphibians.