Molecular phylogeny of Sporochnus pedunculatus (Sporochnaceae, Phaeophyceae) from Atlantic Patagonia based on cox3 and rbcL

Sporochnus is a conspicuous subtidal brown alga and the most speciose genus of the Sporochnaceae. Of the 14 species currently recognized, Sporochnus pedunculatus is the most widely distributed. This species was discovered in Atlantic Patagonia in the 90’s and reported as an introduced seaweed, given that it’s the only representative of the family in this region. Since then, no taxonomic studies have been carried out on these populations. In this study, we used cox3 and rbcL sequence data to evaluate the phylogenetic relationship of S. pedunculatus from Atlantic Patagonia and to determine the phylogeographic structure of the species. Five individuals were collected from a rocky beach in Atlantic Patagonia (40°50' S; 65°06' W) during the austral summer. Morpho-anatomic characteristics of the thalli were registered and their DNA was extracted and sequenced. One partial rbcL and five partial cox3 sequences were newly obtained and aligned with publicly available sequences of Sporochnus. Phylogenies were inferred for each dataset using Maximum Likelihood and Bayesian Inference. Haplotype networks were constructed based on cox3 data. Patagonian specimens reached up to 30 cm in length, with alternate, spiral or pinnated branching, axes were cylindrical or complanate, and receptacles were up to 2.5 mm long with basal or lateral zooidangia. Cox3 phylogeny showed that Patagonian specimens are included in the S. pedunculatus clade (BS = 72; PP = 1), confirming their earlier identification, whereas rbcL phylogeny revealed its close relationship with representatives from Europe, North America and Australia. Seven haplotypes were found (Hd= 0.80; π= 0.007; K2Pmax = 2.5%), none of them was shared between any of the countries included in the analyses. These results suggest a disjunct distribution of cox3 haplotypes of S. pedunculatus, however, given the wide distribution reported for this species, additional molecular data from other regions is needed to resolve its phylogeography.