O boto vermelho: há diferença bioacústica entre as espécies e subespécies do gênero INIA?

Abstract

The Amazon River Dolphin is a representative of the Iniidae family, which currently consists of three species: Inia geoffrensis, I. boliviensis and I. araguaiaensis, and the species I. geoffrensis has two subspecies: I. g. geoffrensis and I. g. humboldtiana. Molecular differences and small morphological characteristics define them as different species and subspecies of Amazon River Dolphin. The bioacoustics can be a tool for the study of species differentiation, particularly through the analyzes of the emitted signals of echolocation, since these are influenced by peculiarities of the morphological structures of the skull. Therefore, their echolocation clicks were analyzed with the aim of identify possible differences in acoustic emissions. The acoustic data collection occurred in the rivers Guaviare (I. g. humboldtiana); Madeira (I. boliviensis, I. g. geoffrensis and hybrids); Xingu (I.g.geoffrensis); and in the Cantão State Park (I. araguaiaensis). The sounds were captured by a Cetacean Research ™ C54XRS (+ 3 / - 20 dB, - 185 dB re: 1V / μPa) hydrophone, static passive pickup, and then the sounds were transferred to a Daq / 3000 Series digitizer board, with frequency of 200 kHz / 24 bits. An acoustic analysis was performed using the software Raven Pro. 1.5 and MatLab R2014A, and the statistical analysis with R program (R CORE TEAM, 2015). In total, 158 clicks were analyzed (5851 clicks) in 86 minutes of recording. In all places recorded, the clicks presented lower frequency averages when compared to previous studies. According to the Kruskal-Wallis test, there was a significant difference among species for all analyzed parameters (p-value <0.001). The Mann-Whitney test was performed to compare the clicks between two sampled sites, through the parameters of peak frequency, and bandwidth in 3 and 10 dB. Only the bandwidth in 3dB between Cantão and Madeira and the peak frequency between Guaviare and Madeira were not significant (p-value> 0.05). The acoustical differences reinforce the species and subspecies separations already described, being another indication that the Iniidae family actually has, at least, three distinct species.