Como a densidade de árvores e o tamanho do corpo influenciam os sinais acústicos no gênero Allobates?

Abstract

Vegetation reflects and absorbs sound waves, creating noise in the acoustic communication between animals that use sound to communicate. Vegetation density can modify air turbulence and has been considered a crucial factor in advertisement calls adaptation. Sound is critical for anuran reproduction, and that is why it must be accurately received by the receiver. The Acoustic Adaptation Hypothesis (AAH) predicts that acoustic signals that are emitted in places with a greater amount of vegetation would be adapted to improve signal transmission, differentiating its spectral and temporal characteristics to try to increase the signal’s effectiveness. In addition, body size can also influence acoustic characteristics. Allobates is a genus of leaf litter frogs, with species that occur in different forest types, which vary in tree density. Here we used two classes of rainforest (dense and open) as a proxy for vegetation density, as the 10 sites studied fell into these two forest categories. We evaluate the hypothesis that tree density affects the evolution of acoustic parameters of 21 species of Allobates from Amazonia. We analyzed 238 advertisement calls of 21 Allobates species from 10 locations on Amazon. Furthermore, we compared the temporal and spectral characteristics between dense and open rainforests using a t-test. We used simple linear regressions to test the influence of size on advertisement calls. Through PGLS we evaluated the effect of the environment on acoustic signals without the phylogenetic effect. Body size correlated 75% with dominant frequency, but contrary to what was expected by the HAA, we did not find an effect of tree density on the evolution of dominant frequency. However, the dominant frequency of denser forest species is lower when compared to more open forests. We found no evidence for the effect of tree density on the evolution of note rate, but rather on body size, a relationship not yet registered for anurans. Our results show strong evidence of the effect of tree density on note duration. Note duration was shorter in denser forests than in open forests, contrary to what was expected by the HAA. In addition, we recorded an unprecedented quadratic relationship between species size and note duration in denser forests, possibly due to the environment. We demonstrate that body size influences both spectral and temporal characteristics of call, and that subtle differences between tropical forests lead to diversification in acoustic parameters in an Amazonian anuran genus. We suggest that further studies should be conducted so that the subtle influence of the environment and body size on acoustic signals is better understood.