Abstract
BackgroundThe acoustic adaptation hypothesis (AAH) states that signals should evolve towards an optimal transmission of the intended information from senders to intended receivers given the environmental constraints of the medium that they traverse. To date, most AAH studies have focused on the effect of stratified vegetation on signal propagation. These studies, based on the AAH, predict that acoustic signals should experience less attenuation and degradation where habitats are less acoustically complex. Here, we explored this effect by including an environmental noise dimension to test some AAH predictions in two clades of widespread amphibians (Bufonidae and Ranidae) that actively use acoustic signals for communication. By using data from 106 species in these clades, we focused on the characterization of the differences in dominant frequency (DF) and frequency contour (i.e., frequency modulation [FM] and harmonic performances) of mating calls and compared them between species that inhabit flowing-water or still-water environments.ResultsAfter including temperature, body size, habitat type and phylogenetic relationships, we found that DF differences among species were explained mostly by body size and habitat structure. We also showed that species living in lentic habitats tend to have advertisement calls characterized by well-defined FM and harmonics. Likewise, our results suggest that flowing-water habitats can constrain the evolutionary trajectories of the frequency-contour traits of advertisement calls in these anurans.ConclusionsOur results may support AAH predictions in frogs that vocalize in noisy habitats because flowing-water environments often produce persistent ambient noise. For instance, these anurans tend to generate vocalizations with less well-defined FM and harmonic traits. These findings may help us understand how noise in the environment can influence natural selection as it shapes acoustic signals in affected species.
Highlights
The acoustic adaptation hypothesis (AAH) states that signals should evolve towards an optimal transmission of the intended information from senders to intended receivers given the environmental constraints of the medium that they traverse
Body size (SVL), and temperature on dominant frequency (DF) We found that flowing-water species (N = 45) had a mean snout-vent length (SVL) of 45.2 ± 24.5 cm and produced advertisement calls with a mean DF of 4.59 ± 3.99 kHz (0.72–19 kHz), while still-water species (N = 61) had an average SVL of 66.8 ± 21.7 cm (25.5–126 cm) and generated advertisement calls with an average DF of 1.69 ± 0.84 kHz (0.35–4.23 kHz)
I.e., Bufonidae and Ranidae, we found that both DF (N = 78, K = 0.32, Z variance = − 3.03, P < 0.001) and SVL (N = 78, K = 0.22, Z variance = − 2.81, P < 0.001) showed a strong phylogenetic signal
Summary
The acoustic adaptation hypothesis (AAH) states that signals should evolve towards an optimal transmission of the intended information from senders to intended receivers given the environmental constraints of the medium that they traverse. According to the acoustic adaptation hypothesis (AAH), natural selection shapes acoustic signals in a way that maximizes their transmission distance and content integrity within the environment in which they are produced [8] These predictions have been supported by evidence of sound signalling in birds and other vertebrates, where their vocalizations evolved to increase propagation and accurate information transmission in specific environments [8,9,10]. In this context, several principles are proposed according to the AAH that characterizes acoustic signals. Signals, when produced closer to the ground, tend to have a frequency range over 500–1000 Hz, which provides them with better propagation properties near the ground [8, 12]
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