Population-level variation in vocalizations of Rana boylii, the foothill yellow-legged frog

Vocalizations are the main form of communication between anurans, and each species can have an array of calls that can range from simple to complex. Local dialects from different populations of the same species can inhibit intraspecific communication, especially when females prefer a specific range of spectral and temporal properties in their mates' calls. Vocal sacs are anatomical features used for communication in anurans and their structure and size are variable among anuran species. Rana boylii, a candidate species under the California Endangered Species Act and the focus of this study, primarily call underwater using small, paired subgular vocal sacs. Most studies of frog vocalizations have focused on aerial calls, partly due to the ease of recording vocalizations above water. Consequently, characterization of R. boylii's call spectrum, as with other taxa that vocalize under water, has proven challenging. One previous study distinguished five R. boylii calls, but did not characterize variation among populations. This study examined variation in spectral (dominant frequency and high frequency) and temporal properties (call duration, pulse number, pulse rate, pulse duration, note number, and note duration) of call types among three disjunct populations of R. boylii. Rana boylii had a substantial amount of variation among populations not only in the spectral and temporal properties of calls, but also in the call types they emit. Two novel call types were described: the chuckle and the warble. Two locations had call types with frequency ranges that peaked above 20 kHz (ultrasonic), which could be a direct effect of the distinct environmental conditions at these sites. Rana boylii's diverse array of calls showed previously undocumented significant differences between populations. The results of this study highlight that different populations of the same species might not possess the same communication strategies.