Gabriel Melo-Santos, Sam Froman Walmsley, Volker B. Deecke, Heloíse Pavanato, Braulio Leon-Lopez, Alexandre F. Azevedo, Diogo Destro Barcellos, Hector Barrios-Garrido, Amandine Bordin, Camila Carvalho de Carvalho, Marta J. Cremer, Kareen De Turris-Morales, Maria Claudia Diazgranados, Camila Domit, Nínive Espinoza-Rodríguez, José Lailson-Brito Jr, Miriam Marmontel, Dalila Teles Leão Martins, Angélica Lúcia Figueiredo Rodrigues, Israel Maciel, Marcos César de Oliveira Santos, Natacha Aguilar de Soto, Rodrigo Hipólito Tardin, Marie Trone, Luz Helena Rodriguez-Vargas, Maria Alice dos Santos Alves, Maria Luisa da Silva, Laura J. May-Collado, Vincent Janik

1. While cetaceans are known to produce large and complex acoustic repertoires, the challenges of exhaustively sampling sounds at sea and counting relevant signals has precluded an understanding of their true repertoire diversity.
2. Here we quantify and compare the whistle repertoires of 16 populations in the genus Sotalia, belonging to two sister species, the Guiana dolphin (Sotalia guianensis) and the tucuxi (Sotalia fluviatilis), both endemic to Latin America. We used an adaptive resonance theory neural network combined with dynamic time-warping (ARTwarp) to categorize whistles into types. Applying recent methods from community ecology, we then determined the size of each population’s repertoire and estimated β-diversity between sites while accounting for differences in sampling effort.
3. Our analysis included a total of 1,817 whistles from 16 populations along the Atlantic coast of Latin America and six in the Amazon Basin, distributed throughout the range of the genus Sotalia. Contrary to previous studies comparing acoustic parameters alone, this whistle contour type based analysis reveals significant differences in the composition of each population’s repertoire, with 21% of types being unique to a single population. We also identified surprisingly large variation in repertoire size, estimating some populations to have up to 20-times more whistle types than others.
4. Our findings reveal substantial intraspecific variation in the whistle repertoires of two sister delphinid species. This suggests that repertoire diversity and size are strongly influenced by population-specific processes, rather than being constant within species. Further application of these methods for comparison across unevenly sampled populations will open the door for new insights into the evolutionary and ecological drivers of odontocete repertoires, and can also be applied to other animal groups.