Genetic variation in the mitochondrial DNA control region among horse mackerel (Trachurus trachurus) from the Atlantic and Mediterranean areas

The horse mackerel Trachurus trachurus is a pelagic fish from the Carangidae family that is distributed in waters of Nororiental Atlantic, including the Mediterranean Sea. This species is of special interest due to its Atlantic–Mediterranean distribution and because of the possible effect of past and present day restrictions to gene flow between these seas. Although pelagic marine fishes generally show little geographical genetic differentiation, some species (and other marine organisms as molluscs and crustaceans) show genetic variation between Atlantic and Mediterranean populations. To study this possible genetic differentiation, 359 individuals belonging to five Atlantic and four Mediterranean samples (eight along the coast of the Iberian Peninsula and one from the Gulf of Cagliari—south of Sardinia) were sequenced for 363 bp of the 5′-end of the mtDNA control region. From those individuals, 143 different haplotypes were identified. Only three of 143 haplotypes were present in all the samples, but with low frequencies (between 0.02 and 0.21), and each sample was almost exclusively represented by a unique group of haplotypes. Estimates of the degree of interpopulational genetic variation were low and not significant which indicates an absence of genetic variation between samples. The analysis of molecular variance (AMOVA) and the nested clade analysis also showed no genetic differentiation between samples and between Atlantic and Mediterranean populations. The genetic homogeneity of the Atlantic and Mediterranean horse mackerel populations is discussed in comparison with previous studies of genetic variation in Trachurus and with regard to their life cycle and migratory capacity.