Shifts in the Ratio of Nonlinear Phenomena Between Advertisement and Aggressive Calls are Influenced by Temperature in the Free-Toed Frog Eleutherodactylus interorbitalis

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Abstract Acoustic communication in anurans exhibits considerable plasticity, yet the role of nonlinear phenomena (NLP) and their environmental modulation remain poorly understood. We investigated the acoustic structure of advertisement and aggressive calls in a free-toed frog from Sinaloa , Mexico. Calls from 24 males were recorded under natural conditions and during playback experiments to test whether vocalizations change in response to conspecific acoustic stimulation, with particular emphasis on NLP. Differences between spontaneous and post-stimulus calls revealed strong contextual modulation, after which relationships between acoustic variables, body size, and ambient temperature were evaluated. Advertisement and aggressive calls differed significantly in temporal and spectral characteristics, with aggressive calls showing greater duration, lower dominant frequency, and increased structural complexity. Dominant frequency in advertisement calls was negatively correlated with body size. NLP were common in both call types; however, aggressive calls showed lower proportion of chaos and shorter frequency jumps. In advertisement calls, several nonlinear components were significantly associated with temperature: chaos, subharmonics, and frequency jumps decreased with increasing temperature, whereas the proportion of harmonics increased. In contrast, aggressive calls did not exhibit significant thermal relationships. This study provides evidence that environmental temperature modulates multiple nonlinear acoustic components in anuran vocalizations. Our findings highlight the bioacoustics flexibility of Eleutherodactylus interorbitalis and suggest that NLP may serve as sensitive indicators of physiological and environmental conditions, contributing to a broader understanding of spectral encoding in amphibian communication.

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