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

S Caballero,M C O Santos,M R Rossi-Santos,F Trujillo,M G Montiel,H Barrios-Garrido,C S Baker,F R Santos,J A Vianna,M Marmontel,S Beltrán-Pedreros

doi:10.5597/lajam00155

Abstract

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. RESUMEN: En este trabajo consideramos aspectos filogeograficos y estructura poblacional de los delfines Sudamericanos Sotalia guianensis

Highlights

IntroductionReconstrucciones filogenéticas de 31 haplotipos únicos basados en el análisis de fragmentos de dos genes mitocondriales (1052 pb) revelaron diferencia genéticas claras entre individuos costeros y de río, consistentes con diferenciación a nivel de especies
RESUMEN: En este trabajo consideramos aspectos filogeográficos y estructura poblacional de los delfines Sudamericanos Sotalia guianensis y Sotalia fluviatilis, utilizando muestras (n = 76) colectadas a lo largo de 9000km de la distribución de dichas especies
Our analysis of molecular variance (AMOVA) results seems to suggest that the Maracaibo Lake population originated from a founder event of individuals from the Colombian Caribbean or that these two populations have differentiated recently, as can be deduced from the significant FST values but the non-significant ΦST values

Summary

Introduction

Reconstrucciones filogenéticas de 31 haplotipos únicos basados en el análisis de fragmentos de dos genes mitocondriales (1052 pb) revelaron diferencia genéticas claras entre individuos costeros y de río, consistentes con diferenciación a nivel de especies. Las poblaciones Amazónicas presentaron la mayor diversidad mitochondrial, sugiriendo un tamaño efectivo (Nef) para esta población sorprendentemente grande y sugiriendo flujo genético actual mediado por hembras entre diversas poblaciones a lo largo del río Amazonas y varios de sus tributarios. The main anthropogenic threat that affects this species is gillnet entanglement, mainly in the Amazonian Estuary (da Silva and Best, 1996a; Beltrán-Pedreros, 1998; Trujillo et al, 2000) In other areas they are killed for shark bait and their eyes and genital organs sold as magical charms (Siciliano, 1994; Meirelles et al, 2010 this volume). We present the first comprehensive description of the phylogeography of Sotalia; investigating the genetic relationships between sister-species and among various populations along the Caribbean and Atlantic Coast of South America and in the Amazonian region based on the analysis of two regions of mitochondrial DNA, the control region (CR) and the cytochrome b (Cyt-b) gene

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