Calling Phenology and Call Structure of Sympatric Treefrogs in Eastern Texas

Abstract

Anurans often call in acoustically complex choruses, which can consist of multiple closely related species. Closely related sympatric species often differ in phenology and the acoustic properties of male advertisement calls, which, in some species, are phenotypically plastic. The tetraploid Eastern Gray Treefrog (Hyla versicolor) originates from multiple, separate hybridization events of the diploid Cope's Gray Treefrog (Hyla chrysoscelis) with now-extinct diploid anurans. The two species are visually indistinguishable, exhibit highly similar ecology and behavior, and co-occur frequently across their range. Males of these species can be distinguished from each other by the structure of their advertisement calls. Daily audio recordings and weather data were collected for five consecutive years from eight breeding sites of sympatric H. versicolor and H. chrysoscelis. We examined spatial and temporal patterns in calling phenology and responses of both species to environmental cues. Additionally, we measured three advertisement call properties to evaluate differences in call structure based on community composition. The phenologies of the two gray treefrog species were nearly identical, and the presence of the other species did not significantly affect call pulse rate or dominant frequency in either species. Chorus composition affected call duration in both species, but in H. chrysoscelis, this effect was temperature dependent. Our results indicate that while calling phenology does not contribute to reproductive isolation in sympatric gray treefrogs, modulation of phenotypically plastic call properties could affect male mating success and prezygotic reproductive isolation.