Correct discrimination between courtship signals could help maintain genetic integrity between closely related species. However, asymmetric usage of signals might cause asymmetric magnitude of gene flow across the contact zone. Buergeria japonica and B. otai are sibling species with parapatric distribution pattern in Taiwan, forming two narrow contact zones in eastern and western sides of the island. Both species use a shared acoustic signal of calls (Type 1a/1b), whereas B. otai presents another unique call type (Type 2) which never appears in B. japonica. Combining behavioral experiments with genome-wide RAD-seq analyses, we aim to test whether the ability of signal recognition influences genetic introgression across their species boundary. The playback experiments showed that the western population of B. otai has evolved a stronger level of reproductive character displacement by showing the inclusive usage of their unique Type 2 signal. In contrast, the eastern population used both unique and shared signals and has a stronger preference for the latter. Consistent with behavioral difference, genetic introgression across the contact zone was detected only in the eastern boundary but not in the western one. Furthermore, the gene flow in this contact zone tends to be unidirectional from B. japonica toward B. otai. Our results support the prediction that a more specialized signal user might have a higher probability to maintain their genetic integrity compared to a generalized signal user.