Individual variation in two types of advertisement calls of Pacific tree frogs, Hyliola (=Pseudacris) regilla, and the implications for sexual selection and species recognition

Anuran advertisement calls play a fundamental role in social interactions related to reproduction, like territory defence and mate attraction. As such, advertisement calls are often shaped by natural and sexual selection. Therefore, to understand the evolution, function, and mechanisms of signal production and perception, it is important to characterise sources and patterns of variation in call properties. We recorded and analysed the two types of advertisement calls produced by Pacific tree frogs, Hyliola regilla: diphasic and monophasic calls. Specifically, we examined (i) the relationship between call properties and both body size and physical condition, (ii) patterns of within- and among-individual variation in call properties, and (iii) acoustic differences between diphasic and monophasic calls. While only one property of diphasic calls correlates with physical condition, spectral properties of both types of calls correlate with body size. Patterns of within- and among-individual variation were similar between call types and, overall, consistent with patterns reported for closely related species. Monophasic calls have lower frequencies, are delivered faster, and have higher call effort and duty cycle than diphasic calls. We discuss our results in relation to sexual selection and formulate hypotheses about the evolution, function, and mechanisms of acoustic communication in Pacific tree frogs.