In anurans, the complexity of courtship calls may effect female mate choice. The current study suggests that nonlinear phenomena (NLP) components can contribute to increasing complexity in courtship calls and attracting female attention. The results of a recent study showed that calls of large odorous frog (Odorrana graminea) contained NLP components. However, whether the nonlinear components of courtship calls in O. graminea improve male attractiveness remains unknown.

We hypothesized that female O. graminea would prefer males producing calls with a higher proportion of NLP components (P-NLP-C). To test this hypothesis, we recorded the advertisement calls of 28 males and confirmed that the P-NLP-C was significantly positively related to body size. We also measured the body size of natural amplectant males and non-amplectant males in the field, and found that amplectant males had larger body sizes than non-amplectant males, and the results of two-choice amplexus experiments similarly revealed a female preference for males with larger body sizes. Additionally, phonotaxis experiments also revealed that females preferred male calls with a high P-NLP-C.

The results suggest that a higher P-NLP-C in calls can enhance male attractiveness, and the P-NLP-C may provide key information about male body conditions for female O. graminea. Our study provides a new insight for better understanding the role of NLP in anuran mate selection.