Phylogeographic characterization of the ribbon worm Lineus sanguineus populations from the Southwestern Atlantic (Heteronemertea: Lineidae): a true case of cosmopolitanism

Abstract Lineus sanguineus (Rathke, 1799) is a cosmopolitan species commonly found on fouling fauna along rocky shores. Along with the larval capability of the pilidium larvae in heteronemerteans, this species can reproduce asexually by fissiparity. The present study utilized a phylogeographic approach combined with Ecological Niche Modeling analysis to evaluate L. sanguineus populations along the Brazilian coast. We used sequences from two mtDNA regions, 16S ribosomal RNA (16SrRNA) and cytochrome c oxidase subunit 1 (COI), and one nuclear region, Internal Transcribed Spacer 1 (ITS-1), of 85 specimens sampled in nine locations. Genetic diversity analysis showed more ITS-1 marker diversity, evidenced by augmented intrapopulation diversity values. There was no clear geographic pattern, and the AMOVA analysis revealed low to moderate genetic structuring and high connectivity between localities, with most of the genetic variation contained within populations (mtDNA AMOVA, FST=0.18, ITS FST=0.33). The pairwise FST results indicate high genetic structuring between the Northeast and localities in the South and Southeast of Atlantic costal zone. This pattern suggests that Brazilian oceanic currents play an important role in species connectivity. The paleodistribution pattern demonstrated that probably the colonization occured from the South to the Northeast of the continent. These results reinforce that sexual reproduction and larval dispersion play a vital role in the connectivity of these Southwest Atlantic populations and that oceanographic currents facilitate these processes.