Testing bioregionalization hypotheses of the Brazilian coast using phylogeography of marine mites

Biogeographic division of the Brazilian coast has been the subject of debates, with alternative hypotheses proposing different borders between provinces or ecoregions. To test these hypotheses, we used halacarid mites, a common component of marine meiofauna, well-suited for this task due to their lack of a planktonic dispersal stage. We sequenced one mitochondrial and two nuclear markers from 427 individuals belonging to three OTUs (Agauopsis bilophus, A. legionium and Rhombognathus levigatoides) from 47 localities. Our data confirmed the main partition of the Brazilian coast into theTropical and Subtropical provinces at the Abrolhos Plateau (~15-20°S), an area that also serves as a transitional zone between the two provinces, with its southern limit where the Vitória-Trindade ridge meets the continent (~20S), deflecting surface currents and thereby serving as a biogeographic barrier. The A. bilophus and R. levigatoides OTUs each formed species-level sister clades, which are distributed according to this division, with the former allopatric, while the later were sympatric at the Abrolhos plateau. We confirmed the following subregions: Amazonian from 4°N to ~2.5°S; Northeast from ~2.5°S to ~7-13°S; East from this point to Abrolhos Plateau (~15°S); the Abrolhos from ~15°S to ~20°S; and the Southeast/South from ~20°S southward.