Genomic analysis of anadromous brown trout (Salmo trutta) reveals new insights into connectivity patterns and population divergence

Abstract

A large body of studies on brown trout genetics currently exists. However, fewer of these studies have been conducted on anadromous brown trout (sea trout) and have been limited to only a few genetic markers like allozymes, mtDNA or microsatellites. Here we analyzed population structure and connectivity in sea trout applying a modern genomic approach, analyzing 503 single nucleotide polymorphic variants (SNP’s) by next generation sequencing. We studied four streams along the Skagerrak coast and found an overall significant population structure (FST = 0.0161; P<0.01) which further seemed to constitute of three genetically distinct sea trout populations which may constitute separate management units. Pair-wise multi locus FST estimates increased with geographical distance, revealed a weak non-significant trend of isolation by distance (Mantel test: r = 0.4823 ,P = 0.1978). The sea trout populations along this coastal stretch showed some variation in genetic diversity, but did not deviate from Hardy-Weinberg equilibrium. One population, Mørfjærbekken, displayed differences in some phenotypic traits i.e., length and k-factor, which may possibly be a result of different selection pressure than the other streams. Finally we discuss our findings in relation to conservation and management implications for sea trout.