Complexidade acústica na comunicação animal e sua influência na ecologia dos cetáceos

Abstract

Biological signals in animal communication are subjected to evolutionary pressures and often can affect the survivorship and reproduction of senders and receivers. The communication via sound production is spread among animals and it has been considered an efficient way to change information. Both the environment and the social context are important forces regulating the properties of acoustic signals. The hypothesis of sociability in communication postulates that with increasing social complexity, animals will present greater complexity in their signals. However, little is known about how the relationships involved in acoustic communication with sociability occur. Animals which have sound as their main sense use a wide variety of signals in all their vital activities, especially in social behaviors, and the link between sociability and acoustic diversity may be related to the evolution of tonal sounds. Thus, the overall objective of the study was to analyze the relationships involved in acoustic communication by evaluating the direct and indirect effects of social complexity on acoustic complexity, mediated by tonal signals, using cetaceans as a model for testing. The statistical technique of Structural Equation Modeling (SEM) was applied, using the variables of group size, group type, and number of calves to measure social complexity; the variables of tonality (dB), amplitude (dB) of the fundamental frequency, maximum frequency (Hz), minimum frequency (Hz), and duration (s) to describe the tonal signals; and the variables of number of inflection points and number of notes to measure acoustic complexity. According to the SEM results, the variables describing the tonal sounds mediated all the effects of the social complexity variables. The significant effects of greatest magnitude came from, mainly, group size and number of calves. The SEM showed that the number of notes had most of its variance (R² = 0.94) explained, receiving effects of greater magnitude from the group size and number of calves. The number of inflection points, on the other hand, had the lowest coefficient of determination (R² = 0.35), which received no significant direct effect from any of the social complexity variables, receiving influence only from the tonal signal descriptor variables. The present study provided a greater understanding of the nature of animal communication, with the communication signals of cetaceans presenting functions for the interactions that predominate in their societies, with a clear relationship between social structures and tonal signals acoustic diversity seen in the most different groups of this taxon, demonstrating a possible modeling framework to be applied to communicative systems.