Why Are Most Fish Populations Genetically Homogeneous Along the Southwestern Atlantic Coast? The Role of Life History Traits in Shaping Genetic Patterns

Abstract

Aim Investigate patterns of population genetic structure in Southwestern Atlantic marine fishes and evaluate how geographic range, habitat diversity, and evolutionary history shape population connectivity. Location Southwestern Atlantic, including the Caribbean, Brazilian coast, and Patagonian region, between 0°59′ N and 40°16′ S. Period Studies published between 1980 and 2023. Main Taxa Studied With 84 species of marine, reef‐associated, and estuarine fishes either resident or transiently associated. Methods A systematic review and synthesis were conducted using a predefined Boolean search across several bibliographic databases, which initially retrieved 47 scientific papers. Based on the available literature, we categorized the species identified in these articles according to their biological, ecological, and evolutionary traits. Subsequently, a Generalized Additive Model (GAM) was employed to model species distribution and evaluate the effects of genetic breaks on fish populations. Results Most species exhibited high genetic homogeneity among populations from the Caribbean, Brazilian coast, Patagonia, and northern and northeastern Brazil, indicating extensive connectivity; however, a recurrent interruption in gene flow near 20° S, adjacent to Espírito Santo State, suggests the presence of biogeographic barriers, while differential use of reef and estuarine habitats and speciation timing were key determinants of genetic structuring; high connectivity was largely associated with pelagic egg production, the influence of major coastal currents such as the Brazil Current, benthopelagic behaviour, and rafting‐mediated larval dispersal. Main Conclusions Oceanographic processes and species‐specific biological traits jointly shape the genetic responses of marine fishes and maintain broad‐scale connectivity in the Western Atlantic, although localized disruptions in gene flow persist and require further investigation to support effective conservation and management strategies.

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