Assessment of the acoustic adaptation hypothesis in frogs using large‐scale citizen science data

Acoustic communication is vital to the survival and fitness of many vertebrates. While successful communication is reliant on acoustic signals reaching an intended receiver and maintaining content fidelity, propagating signals are attenuated by environmental factors such as habitat type. The acoustic adaptation hypothesis (AAH) predicts that the acoustic properties of signals are selected for optimal transmission in the habitats in which they propagate. To date, consistent evidence to support the theory is lacking, but studies have typically been primarily based on localized datasets with small sample sizes. Citizen science is emerging as a potential means to overcome the challenges associated with broad‐scale sampling, allowing us to assess the validity of the AAH in frogs on a continental scale. We analysed the male advertisement calls of 674 individual banjo frogs (Limnodynastes dorsalis, L. dumerilii, L. interioris and L. terraereginae) from across their range, pairing these citizen science data with remotely sensed measures of habitat complexity. While we detected considerable variation in acoustic structure within and among banjo frog species, this was not strongly correlated with habitat complexity. Thus, we found no support for the AAH. However, with our study spanning an area of over 1.7 million km2, we conducted the largest‐scale test of the AAH in frogs to date, contributing to the global understanding of acoustic signal evolution. Acoustic communication in animals is integral for individual survival and fitness, but successful communication can be impacted by a range of abiotic and biotic factors, including the physical structure of the environment. We test the validity of the acoustic adaptation hypothesis (AAH), that the acoustic properties of signals are selected for optimal transmission in the habitats in which they propagate, using large‐scale citizen science data and remote satellite imagery. In the largest‐scale test of the AAH in frogs to date, we find no support for the AAH.