Influence of stream geophony and social contexts on the communication of Hylodes perere (Anura: Hylodidae)

Abstract

Animal communication involves the emission and reception of signals among individuals in an environment. In anuran amphibians, acoustic signals are the main signal used in communication, which mediate social interactions in reproductive and aggressive contexts. In territorial species such as the torrent frogs of the genus Hylodes (Anura: Hylodidae), distinct signals and behavioral strategies are used in conditions in which individuals are exposed to stream background sounds (geophony). However, whether calling males maximize acoustic communication in this situation by adjusting their calls or by moving to quieter section is still uncertain. Hylodes perere is a torrent frog endemic from the highly endangered Atlantic Rainforest domain, southeastern Brazil, and individuals breed only in streams with rapids. The species is currently Not Categorized by the IUCN and Data Deficient by the ICMBio, which indicates that little is known about its calling repertoire and reproductive behavior. Using this species as a model, we investigated the influence of stream geophony on its calling behavior. We marked males and tested if they remain in their territories and thus adjust their advertisement calls to maximize their communication. We also described territorial calls with information on the territories, periods of the day, microhabitats and social contexts of emission. We recorded individuals in audio and video, measured spectral and temporal call parameters, sound pressure levels of calls and stream sounds, and body size and environmental temperatures. We ran mixed linear and generalized models to verify the relation between these variables. We found that males remained in the same location across time and increased call intensity in noisier situations, but did not reduce calling effort in these situations. Males also increased the dominant frequency of calls in response to stream noise. Territorial calls were formed by two types of notes that were emitted alone (simple territorial calls) or together in eight possible combinations (complex territorial calls) in all periods of the day and microhabitats, but varied depending on the social contexts. Conspecific males interacted by emitting advertisement and territorial calls in short and long distances, also preceding a physical combat. These calls were also emitted during a courtship. Taken together, our results indicate that territoriality is an important factor for males to the point where they change their advertisement calls to surpass stream noise but not move along the stream. However, the fact that they do not reduce call effort indicates that sexual selection mechanisms are key in this system. Territory defense, to which these calls largely contribute, is likely advantageous for H. perere for survival and especially reproduction. Our results confirm that communication in the species is complex, opening possibilities for behavioral studies with species of the genus Hylodes and aiding in research of the communication evolution within the family.