Nonlinear Phenomena Conveying Body Size Information and Improving Attractiveness of the Courtship Calls in the Males of Odorrana tormota

Nonlinear phenomena are commonly shown in the vocalization of animals and exerts different adaptive functions. Although some studies have pointed out that nonlinear phenomena can enhance the individual identification of male Odorrana tormota, whether the nonlinear phenomena play a specific role in the sexual selection of O. tormota remain unclear. Here we presented evidence that there was a significant negative correlation (Pearson: n = 30, r = 0.65, P < 0.001) between the nonlinear phenomena content and snout-vent length in the male O. tormota, and two-choice amplexus experiments showed that female O. tormota preferred male with smaller body size containing higher nonlinear phenomena content in its calls. Phonotaxis experiments also revealed that females preferred calls with higher nonlinear phenomena content. Additionally, compared to the calls with lower nonlinear phenomena content and higher fundamental frequency, there was shorter response time in phonotactic behaviour of female induced by the calls with higher nonlinear phenomena content and lower fundamental frequency. We argue that the nonlinear phenomena content in the calls of male O. tormota can convey its body size information and may provide important clues for female frogs in darkened surroundings to identify males' body size during mate choice, meanwhile, higher nonlinear phenomena content in males' calls may increase the attractiveness of males to females. The results of this study provide confirmation that, for O. tormota, nonlinear phenomena have specific function in mate choice.

Automated summary

Nonlinear phenomena in the vocalization of male Odorrana tormota are negatively correlated with body size, with females preferring smaller males with higher nonlinear content. Females also show a preference for calls with higher nonlinear content, indicating a role for nonlinear phenomena in mate choice and attractiveness. These findings suggest that nonlinear phenomena play a specific function in sexual selection in O. tormota.