Murky mysteries: population structure and gene flow of the estuarine darter goby (Ctenogobius boleosoma)

Abstract The darter goby ( Ctenogobius boleosoma ) is a small species of fish that is part of the order Gobiiformes, whose taxonomy and description are regularly the subject of debate. Ctenogobius boleosoma is a euryhaline species with a large estuarine distribution within the western Atlantic Ocean, spanning from southern Brazil to as far as New Jersey, USA, in the Northwestern Atlantic. Members of the genus Ctenogobius as a whole are understudied, with some members considered imperiled or threatened. Despite their wide range, lack of data, and potential interest to conservation, no population genetic study has focused on any member of Ctenogobius . With this in mind, we collected 55 C. boleosoma from across their range and sequenced 1333 single nucleotide polymorphisms to study patterns of potential population structure within the Gulf of Mexico and western Atlantic Ocean. Because they lay demersal eggs and are distributed across multiple river outflows, we expected high levels of population structure within the Gulf of Mexico. Instead, we found that structure was very clear at a large scale in the Atlantic Ocean, but admixed at a smaller scale, like within the Gulf of Mexico. Using discriminant analysis of principal components, ADMIXTURE, and measures of fixation index, we found evidence of population structure between the samples we collected between the Northwestern Atlantic samples and those we included from the Caribbean and Southern Atlantic.