Abstract
Gilthead sea bream is an important target for both recreational and commercial fishing in Europe, where it is also one of the most important cultured fish. Its distribution ranges from the Mediterranean to the African and European coasts of the North-East Atlantic. Until now, the population genetic structure of this species in the wild has largely been studied using microsatellite DNA markers, with minimal genetic differentiation being detected. In this geographically widespread study, 958 wild gilthead sea bream from 23 locations within the Mediterranean Sea and Atlantic Ocean were genotyped at 1159 genome-wide SNP markers by RAD sequencing. Outlier analyses identified 18 loci potentially under selection. Neutral marker analyses identified weak subdivision into three genetic clusters: Atlantic, West, and East Mediterranean. The latter group could be further subdivided into an Ionian/Adriatic and an Aegean group using the outlier markers alone. Seascape analysis suggested that this differentiation was mainly due to difference in salinity, this being also supported by preliminary genomic functional analysis. These results are of fundamental importance for the development of proper management of this species in the wild and are a first step toward the study of the potential genetic impact of the sea bream aquaculture industry.
Highlights
Seen from a “terrestrial” perspective, the marine environment looks like a vast space with no barriers to limit the movements of the organism that inhabit it
While the marine environment appears to be a continuous space with no barrier to gene flow, increasing data support the hypothesis that marine animal populations are structured by oceanographic, historical and other environmental factors
We employed a genome wide single nucleotide polymorphisms (SNPs) based analysis to more clearly describe the genetic structure of wild gilthead sea bream populations from the Mediterranean Sea and Atlantic Ocean
Summary
Seen from a “terrestrial” perspective, the marine environment looks like a vast space with no barriers to limit the movements of the organism that inhabit it. The greater number of informative markers that that are detectable by these new approaches increases the chances of detecting genomic regions under selective pressure [2, 7, 8] allowing the investigation of demographic vs environmental causes of genetic differentiation among populations Such molecular markers can be exploited for the geographical traceability of wild samples, applicable in actions against illegal, unreported and unregulated (IUU) fishing as well addressing the increased interest of customers regarding food origin. The results are discussed in context of the life history of the species and previous knowledge of sea bream’s population genetics to Population genetic structure of gilthead sea bream provide a valuable baseline for the future management of wild stocks and for the assessment of potential impacts of aquaculture on the genetics of the species
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