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Abstract

An invasive lineage of sculpins was recently found to spread in major rivers in the Europe. It is assumed to have originated during the last 250 years from hybridization between Cottus rhenanus and Cottus perifretum, and has adapted to big river habitats that are not accessible for parental species, whose habitats are limited to headwaters and small streams. Previous studies have found transgressive gene expression patterns in the invasive sculpins compared to parental species, but the genetic basis remains unknown. In this study we employed the Depth of Coverage (DOC) approach, which estimate copy numbers of a target by analyzing relative sequencing depth signal in the next generation sequencing (NGS) datasets, to evaluate the genome sizes of individuals and to test if hybrid specific de novo mutational processes besides recombination of standing genetic variations of the parental species contributed to the evolution of the invasive sculpin genome. We observed a 10% genome size expansion, proliferations of several retrotransposons, and copy number increase of the set of candidate adaptive genes. The results suggest hybrid specific mutations especially copy number variations (CNVs) of multi-copy genes may play important roles in the fast adaptive evolution of invasive sculpins and may lead to hybrid speciation, and raises new questions on the complex origin of the invasive lineage.