Mitochondrial DNA diversity, differentiation and phylogeography of the South American riverine and coastal dolphins Sotalia fluviatilis and Sotalia guianensis.

Here we consider the phylogeography and population structure of the South American coastal and riverine dolphins, Sotalia guianensis and Sotalia fluviatilis, based on samples (n = 76) collected across more than 9000km of the species distribution. Phylogenetic reconstruction of 31 distinct haplotypes based on a combined analysis of two mitochondrial gene fragments (1052bp) revealed clear genetic differences between riverine and coastal individuals consistent with species-level ranking. Within the coastal species, a spatial analysis of molecular variance of the control region sequences showed significant regional population differentiation (FST = 0.4; FST = 0.6; P<0.001). The highest mitochondrial diversity among costal population units was found along the Caribbean Coast of Colombia and Venezuela. The genetic distinctiveness of the Maracaibo Lake (Venezuela) population has conservation implications regarding the threats faced by the animals in this region, including oil exploitation. Brazilian populations of Sotalia showed the lowest mitochondrial diversity and differentiation among the coastal species warranting further investigation. The Amazonian populations showed the highest mitochondrial diversity overall, suggesting a surprisingly large effective population size (Nef) and relatively high female gene flow throughout the sampled regions of the main river and its tributaries. From our results, at least two different conservation strategies need to be developed for each of the proposed sister-species. For the coastal groups, characterized by restricted gene flow and very localized populations along the Caribbean and Atlantic Coast of South America, it is advisable to work at a local level in order to improve the fishing practices and prevent frequent dolphin entanglement in nets. For the Amazonian groups, priority must be given to maintain the connectivity detected between regions. Obstacles to connectivity, including hydroelectric and dam construction, as well as excessive boat traffic, could affect the future of these populations.