Variação ambiental e geográfica nos assobios de Tucuxi (Sotalia fluviatilis)

Abstract

The tucuxi (Sotalia fluviatilis) is the only species of the Delphinidae family to live exclusively in freshwater environments and is widely distributed throughout the Amazon basin. Delphinidae use sound signals as their main resource in social interactions. Identifying how tucuxi use these communication signals in different environments and different regions throughout their distribution, helps us understand the patterns in habitat use of the species, as well as variation levels of their population. The main goal of this study is to examine the variations of physical parameters in S. fluviatilis whistling behavior in different types of water and in different regions of their distribution. Variations between water types were tested using recordings conducted at two river junctions: black and white water rivers in Manaus – Amazonas and clear and white water rivers in Santarém – Pará. To verify population variation, recordings were conducted at four geographically distant regions (Beruri, Manacapuru and Manaus – in the state of Amazonas; and Santarém – in the state of Pará). Ten acoustic parameters of the fundamental frequency of whistles were extracted for analysis: initial, final, minimum, maximum, ½, ¼, and ¾ frequencies, delta frequency, signal duration, and number of inflection points. PERMANOVA was used as test and post hoc. The post hoc was performed using exclusion and re-inclusion of acoustic variables. Whistles had significantly higher frequencies in blackwater than in whitewater. Whistles emitted in clearwater were higher pitched than those in whitewater, but depended on specific acoustic parameters to produce significant differences. In the geographic variation analysis, the population of Santarém was significantly different from the other regions. Manaus and Beruri demonstrated significant differences; however, Manaus and Manacapuru, as well as Manacapuru and Beruri, did not demonstrate significant differences. In this study we observed that tucuxi adapt their signals to optimize social communication and avoid sound degradation depending on the environment. The variations between populations can be a result of genetic or environmental factors.