Evaluating the boundaries of marine biogeographic regions of the Southwestern Atlantic using halacarid mites (Halacaridae), meiobenthic organisms with a low dispersal potential

Aim We evaluated traditional biogeographic boundaries of coastal marine
regions in SW Atlantic using DNA sequence data from common, rocky-shore
inhabiting, marine mites of the genera Agauopsis and Rhombognathus, family
Halacaridae. Methods We investigated geographic population genetic
structure using CO1 gene sequences, estimated divergence times using a
multigene dataset and absolute time-calibrated molecular clock analyses,
and performed environmental niche modeling (ENM) of common marine mite
species. Results Agauopsis legionium has a shallow history (2.01 Ma) with
four geographically differentiated groups. Two of them corresponded to the
traditional Amazonian and Northeastern ecoregions, but the boundary
between the two other groups was inferred at the Abrolhos Plateau, not
Cabo Frio. Rhombognathus levigatoides s. lat. was represented by two
cryptic species that diverged 7.22 (multilocus data) or 10.01 Ma (CO1-only
analyses), with their boundary, again at the Abrolhos Plateau. ENM showed
that A. legionium has suitable habitats scattered along the coast, while
the two R. levigatoides cryptic species differ considerably in their
niches, especially in parameters related to upwelling. This indicates that
genetic isolation associated with the Abrolhos Plateau occurred in both
lineages, but for the R. levigatoides species complex, ecological niche
specialization was also an important factor. Main conclusions Our study
suggests that the major biogeographic boundary in the Southwestern
Atlantic lies not at Cabo Frio but at the Abrolhos Plateau. There, two
biogeographically relevant factors meet: (i) changes in current directions
(which limit dispersal) and (ii) abrupt changes in environmental
parameters associated with the South Atlantic Central Waters (SACW)
upwelling (offering distinct ecological niches). We suggest that our
result represents a general biogeographic pattern because a barrier at the
Abrolhos Plateau was found previously for the fish genus Macrodon
(phylogeographic data), prosobranch mollusks, ascidians, and reef fishes
(community-level data).