Molecular evidence of the presence of Dictyota dichotoma (Dictyotales: Phaeophyceae)in Argentina based on sequences from mtDNA and cpDNA and a discussion of its possible origin

Dictyota is a brown algae genus inhabiting tropical to warm temperate environments where it is an important food source, shelter and substrate to several species of invertebrates and other algae. The taxonomy of this genus is troublesome, with por species delimitation and doubtful records in the literature. Dictyota dichotoma, the type species of the genus, was commonly accepted as a cosmopolitan species because of the inaccurate geographical distributional range as a consequence of misidentification in several parts of the world. Recent studies with molecular data revealed new species and a new understanding of the evolution and biogeography of the genus Dictyota. These studies confined natural populations of D. dichotoma to Europe (Atlantic and Mediterranean coasts)and Macaronesian islands (Azores, Madeira and Canary archipelagos). Also, they confirmed its presence in South Africa, but whether the species was native or introduced in South Africa could not be verified. In the present study two regions of cpDNA (psbA, rbcL)and one región of mtDNA (nad1)from Argentinian samples, identified morphologically as D. dichotoma, were analysed and compared to other Dictyota species. The identity of these samples as D. dichotoma was confirmed. A haplotype network analysis using all available psbA sequences distinguished seven haplotypes divided into two geographic groups: Atlantic-Mediterranean and Canarian. In Argentina and South Africa only the most common haplotype of the Atlantic-Mediterranean group was observed. According to the paleoceanographic currents and the presence of a European haplotype, the introduced nature of D. dichotoma is indicated.