Multispecies genetic approach reveals divergent connectivity patterns in marine fish from Western Atlantic

Traditionally, the apparent paucity of biogeographic barriers in marine environments when compared to terrestrial and freshwater habitats has been associated with high gene flow rates among geographically distant populations. However, physical traits such as tide currents, temperature, and salinity levels may serve as ecological boundaries thus leading to restricted-range phylogeographic patterns (e.g., the outflow plume from the Amazonas-Orinoco rivers between the Caribbean and the Brazilian Province) according to adaptive features of coastal organisms. To assess the degree of cohesiveness among populations and species of marine and estuarine fishes along a latitudinal gradient from Western South Atlantic, we carried out comparative phylogenetic and species delimitation analyses based on Cytochrome C Oxidase I (COI) sequences of 34 fish taxa from the Caribbean and Brazilian coasts. Distinct values of genetic diversity were revealed for both Provinces, ranging from moderate (1 to 2%) to high (≥ 2%) in 11.76% and 20.59% of the analyzed taxa, respectively. Furthermore, a significant genetic differentiation was observed within the nominal taxa Diapterus auratus, Citharichthys spilopterus, and Scorpaena plumieri from the Caribbean, as well as for Haemulon plumierii between the Caribbean and Brazilian Provinces. Such divergence is likely to result from temporal isolation among local populations during sea-level fluctuations during the Pliocene-Pleistocene period. The present findings demonstrate that similar biogeographic boundaries may result in species-specific patterns of genetic connectivity, possibly associated with ecological constraints. Since molecular operational taxonomic units (MOTUs) were identified in certain formal taxa from both Provinces, a systematic revision of these groups is highly recommended. At last, multispecies COI data proved to be helpful to phylogeographic inferences and to support appropriate policies for the conservation of natural resources.