Population structure of the Common Snook: Evidence of genetic isolation in the Gulf of Mexico and connectivity across the western Atlantic

ABSTRACT Objective The Common Snook Centropomus undecimalis is a species widely distributed throughout the western Atlantic, playing a key ecological role in coastal and estuarine ecosystems. Despite its broad distribution from Florida to southeastern Brazil, little is known about the genetic patterns underlying its population connectivity. This study aimed to characterize the genetic structure of this species and to infer patterns of genetic diversity and connectivity across its range. Methods A total of 100 individuals collected from Florida to southeastern Brazil were genotyped at 11 microsatellite loci. Genetic structure was assessed using Bayesian clustering analysis, discriminant analysis of principal components, and analysis of molecular variance. Genetic differentiation among populations was estimated by pairwise FST, and recent gene flow was inferred from migration proportions among the identified genetic profiles. Results Three distinct genetic profiles were identified: one exclusive to the southern Gulf of Mexico (Gulf Profile) and two along the Atlantic coast (Northern and Southern profiles), both contributing to a central mixed zone in northern South America. Analysis of molecular variance revealed greater variation within populations (68.8%). When admixed individuals (<80% assignment) were excluded, the variation among groups increased to 27.2%, while within-group variation remained high (68.4%). The Gulf Profile showed strong differentiation from the others (FST = 0.33–0.39), whereas differentiation between the Northern and Southern profiles was lower but significant (FST = 0.038). Recent migration analysis indicated high genetic self-recruitment within each profile (68–99%) and limited gene flow among them, except for significant migration from the Southern Profile to the Northern Profile (migration rate = 0.301). Genetic diversity was high across all profiles, with greater allelic richness and heterozygosity in the Gulf Profile and lower values in the Southern Profile; 90 private alleles were identified, most of them in the Gulf Profile. Conclusions The Common Snook exhibits an isolated stock in the southern Gulf of Mexico, likely maintained by historical processes and local oceanographic dynamics, such as the Loop Current and cyclonic vortices. Along the Atlantic coast, two distinct genetic profiles (Northern and Southern) are connected by a transitional zone in northern South America characterized by extensive genetic admixture. Atlantic connectivity appears to be facilitated by ocean currents and the species’ broad ecological plasticity, including tolerance to salinity variation and diadromous migrations. These findings provide valuable insights for conservation and fisheries management strategies throughout the distributional range of this species.