Mitochondrial DNA variation, phylogenetic relationships, and evolution of four Mediterranean genera of soles (Soleidae, Pleuronectiformes)

To increase knowledge about the systematics and evolution of Mediterranean soles, we assessed mitochondrial DNA variation, molecular phylogeny, and ev olution in eight species from the genera Solen, Microchirus, Monochirus, an d Buglossidium by large ribosomal subunit (16S) and cytochrome b (cytb) seq uence analysis. Relevant molecular features are the great variation of base composition among species at the third codon in cytb and the heterogeneity of the nucleotide substitution rate. Phylogenies recovered using 16S nucle otide and cytb amino acid sequences agree with those based on morphology in assessing monophyly of Solea species and ancestry of Buglossidium luteum, but they are against the intergeneric differentiation of Microchirus and Mo nochirus. Conversely, phylogenetic trees based on cytb nucleotide sequences yielded relationships among taxa regardless of their evolutionary historie s. The incongruities between morphological and molecular issues suggest the need for reassessing the systematic value of some morphological characters . Approximate estimates of the divergence time of Mediterranean soleid line ages range from 40 to 13 Mya (Oligocene-Miocene), indicating an ancient ori gin for the group.