Call divergence in three sympatric Rattus species.

To reduce errors in species recognition and the probability of interbreeding that lowers fitness, individuals within sympatric zones shift the signals to differentiate from those of other species. In the present study, the differences of the acoustic features of ultrasounds (courtship calls during heterosexual encounters) and audible calls (distress calls during tail-clamp stress) are compared among three sympatric Rattus species (Rattus andamanensis, R. norvegicus, and R. losea). Results showed that the three species have significantly different call parameters, including call duration, peak frequency, bandwidth, pitch, goodness of pitch, frequency modulation, and Wiener entropy. This study provides quantitative evidence for character displacement in the acoustic signals of closely related sympatric Rattus species. Results indicate that the divergence of acoustic signal has arrived at the quite meticulous degree of evolution. Therefore, the acoustic signal trait is likely involved in the evolution of species diversity in rodents.