Uncoupled Evolutionary Patterns in Spectral and Temporal Components of Acoustic Signals in Anurans Associated With Streams

The use of high-pitched auditory signals by species communicating alongside noisy streams has been often considered an adaptation, yet studies testing this hypothesis have yielded inconclusive results. The major challenge has been to quantify the proportion of across-species signal variation that could be attributed to either common history (phylogenetic load) or adaptation. We further advance in this approach by comparing the phylogenetic load between different components of anuran calls. Because stream noise allegedly represents a stronger selective pressure for call frequency than for call temporal traits, we predicted a weaker phylogenetic signal in call frequency, particularly in the taxa that breed alongside streams. We first built a phylogenetic hypothesis using four mitochondrial genes on each of three clades: the genus Hyloscirtus and the family Centrolenidae, which call alongside streams and the subfamily Phyllomedusinae, known to call at lentic water bodies. In parallel, we compiled data on the advertisement calls of 154 species and used them to calculate Blomberg's K values as a proxy for the phylogenetic load (signal) of the call traits. The phylogenetic signal was weaker in spectral than in temporal call traits within the Hyloscirtus calls and weak or absent in both spectral and temporal components of Phyllomedusine calls. Against our expectations, the phylogenetic signal was strong in call frequency, but absent in call temporal components of the centrolenid calls. Our results support uncoupled evolution between spectral and temporal components of anuran calls. They also indicate that the selective role of abiotic noise varies among taxa and that other factors must be invoked to fully understand among-species variation in advertisement calls.