Correlation Between Environmental Factors, a Life History Trait, Phenotypic Cohesion, and Gene Flow Levels in Natural Populations of Micropogonias furnieri: Is Salinity the Main Factor Driving Divergence?

Abstract

Marine fish are commonly considered to be characterized by limited population structure because of the absence of geographic barriers and the subsequent high levels of gene flow. In spite of this general observation, many cases of genetic geographical divergence have been observed, and natural selection has been suggested to be a causal factor. The white croaker, Micropogonias furnieri, constitutes an excellent model to test for adaptive hypotheses of population divergence, because of its wide geographic distribution along the southwestern Atlantic Ocean. The main objective of this study was to analyze the possible effect of natural selection at the genetic level, using microsatellite loci as molecular markers, and to evaluate the effect of environmental variables, trophic preferences, and phenotypic cohesion on the population structure of M. furnieri. The outlier loci analyses suggested that some of the microsatellites analyzed were under divergent selective regimens, and analyses of population genetic structure considering only these loci revealed a stronger differentiation pattern in almost cases than results compared to those obtained with the entire microsatellite data set. Results obtained also revealed a correlation between phenotypic cohesion, salinity, and temperature with genetic structure in white croakers. These results support previous works which proposed that white croakers inhabiting the Rio de la Plata estuary constitute a different evolutionary unit, maintained to some extent by selective processes.