Date: 17 Aug 2010

Molecular Phylogenetic and Population Genetic Structuring of Macrodon sp., a Coastal and Estuarine Fish of the Western Atlantic Ocean

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Abstract

The study on fish fauna of the Caeté estuary led to a large-scale phylogenetic analysis of one of its common fish species, Macrodon ancylodon. Phylogeographic patterns in M. ancylodon sampled from 16 locations in the subtropical and tropical western Atlantic Ocean were investigated using mitochondrial DNA 16S rRNA and cytochrome b sequences. The analysis shows two monophyletic and highly differentiated lineages of Macrodon populations in the western Atlantic Ocean, and there was no zone of overlap between the two groups, which were geographically separated in the region of South Bahia (Porto Seguro) and north Espirito Santo (Vitoria). Tropical and subtropical groups of Macrodon show nucleotide divergences for the 16S gene varying from 2.4 to 3.5%, a magnitude of genetic divergences usually observed between distinct species of Sciaenidae. The high values of divergence observed between the two groups, coupled with the clearly geographic isolation between them, strongly support our conclusions that these groups should be considered distinct species, M. ancylodon (Bloch and Schneider 1801) being the species of the tropical region (Venezuela to Bahia) and Macrodon sp. the new species of the subtropical region (Espirito Santo to Argentina). Curiously, assuming a constant rate of 1% of divergence per million years for the 16S rRNA, estimation obtained by the comparison of Panama trans-isthmian geminate species of Centropomus, we estimate that the separation between the tropical and subtropical groups of Macrodon have possibly occurred between 2.4 and 3.5 million years ago, during the late Pliocene. These genetic evidences strongly indicate a taxonomic revision of this estuarine-dependent group of fishes.