Testing the acoustic adaptation hypothesis with vocalizations from three mongoose species

Abstract

Acoustic signals degrade and attenuate as they propagate through the environment, thus transmitting information with lower efficiency. The acoustic adaptation hypothesis (AAH) states that selection should shape the vocalizations of a species to maximize transmission through their habitat. A specific prediction of the AAH is that vocalizations will transmit better when emitted in their native habitat versus non-native habitats. We tested this prediction using vocalizations of three mongoose species that dwell in structurally different habitats: banded mongooses, Mungos mungo, dwarf mongooses, Helogale parvula, and meerkats, Suricata suricatta. Representative vocalizations of the three species were broadcast and rerecorded in each habitat at six distances from the source. Rerecorded vocalizations were compared to nondegraded calls through spectrogram correlation. Using generalized linear mixed models, we then quantified the differences in transmission fidelity of each species' vocalizations. Overall, we found partial support for the AAH within the mongoose family: habitat type strongly affected sound transmission, but depending on the species, vocalizations did not always transmit best in their native habitat, suggesting various degrees of acoustic adaptation. Vegetation cover within habitat type was also found to have a significant influence on the transmission properties of vocalizations. In addition, we found evidence that by changing their behaviour, either by producing vocalizations at different amplitudes or by choosing a specific calling location, mongooses can reduce sound degradation and attenuation over distance, thereby enhancing their communication efficiency. Our work highlights how habitat features may be key determinants of vocalization structure in mongooses, and is generalizable to other species living in similar conditions. It also suggests that, given a species and habitat, other selective pressures might prevail and limit acoustic adaptation in animal communication systems. Finally, our study provides insights into how mammals can adjust their vocal behaviour to compensate for environmental constraints on the transmission of their vocalizations.