The Neural Basis of Dip Listening in Treefrogs

Abstract

Each breeding season, frogs face the challenge of effectively communicating in noisy social environments, known as the cocktail party problem. In acoustically dense breeding choruses, different species produce advertisement calls that potentially overlap in time or frequency, interfering with the females’ perception of the calls. Natural fluctuations in the amplitude of the interfering noise may allow females to catch acoustic glimpses of the males’ calls. Females can take advantage of these dips to assess call characteristics like frequency, or separation of calls or pulses. By listening in the dips, females achieve a release from the masking and can detect and distinguish the call of an appropriate mate. While these results are grounded in behavioral studies, more research is needed in order to elucidate the neurophysiological bases of these mechanisms among Anurans, specifically in green treefrogs, Hyla cinerea, and Cope’s gray treefrogs, Hyla chrysoscelis. Here we show both species and the modulation rate of SAM maskers significantly affect the amount of masking release experienced by female frogs. On average, females of H. chrysoscelis detected calls at lower thresholds than females of H. cinerea. As in behavioral studies, calls coupled with noise of slower modulation rates tended to be detected at lower thresholds than those paired with higher frequency maskers. While species and masker modulation rates proved significant, the placement of calls in the peak or dip of the maskers did not. Though some of our results align with previous behavioral studies, other critical aspects are inconsistent with the dip listening hypothesis. These discrepancies may be due to the effects of seasonal plasticity.