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Auditory streaming involves perceptually assigning overlapping sound sequences to their respective sources. Although critical for acoustic communication, few studies have investigated the role of auditory streaming in nonhuman animals. This study used the rhythmic masking release paradigm to investigate auditory streaming in Cope's gray treefrog (Hyla chrysoscelis). In this paradigm, the temporal rhythm of a Target sequence is masked in the presence of a Distractor sequence. A release from masking can be induced by adding a Captor sequence that perceptually “captures” the Distractor into an auditory stream segregated from the Target. Here, the Target was a sequence of repeated pulses mimicking the rhythm of the species' advertisement call. Gravid females exhibited robust phonotaxis to the Target alone, but responses declined significantly when Target pulses were interleaved with those of a Distractor at the same frequency, indicating the Target's attractive temporal rhythm was masked. However, addition of a remote-frequency Captor resulted in a significant increase in responses to the Target, suggesting the Target could be segregated from a separate stream consisting of integrated Distractor and Captor sequences. This result sheds light on how auditory streaming may facilitate acoustic communication in frogs and other animals. 

ABSTRACT Sexual traits that promote species recognition are important drivers of reproductive isolation, especially among closely related species. Identifying neural processes that shape species differences in recognition is crucial for understanding the causal mechanisms of reproductive isolation. Temporal patterns are salient features of sexual signals that are widely used in species recognition by several taxa, including anurans. Recent advances in our understanding of temporal processing by the anuran auditory system provide an opportunity to investigate the neural basis of species-specific recognition. The anuran inferior colliculus consists of neurons that are selective for temporal features of calls. Of potential relevance are auditory neurons known as interval-counting neurons (ICNs) that are often selective for the pulse rate of conspecific advertisement calls. Here, we tested the hypothesis that ICNs mediate acoustic species recognition by exploiting the known differences in temporal selectivity in two cryptic species of gray treefrog (Hyla chrysoscelis and Hyla versicolor). We examined the extent to which the threshold number of pulses required to elicit behavioral responses from females and neural responses from ICNs was similar within each species but potentially different between the two species. In support of our hypothesis, we found that a species difference in behavioral pulse number thresholds closely matched the species difference in neural pulse number thresholds. However, this relationship held only for ICNs that exhibited band-pass tuning for conspecific pulse rates. Together, these findings suggest that differences in temporal processing of a subset of ICNs provide a mechanistic explanation for reproductive isolation between two cryptic treefrog species.