The grayling genome reveals selection on gene expression regulation after whole genome duplication

Genome doubling events have played a significant role in the evolution of vertebrate genomes as the resulting functional redundancy is believed to provide a raw material for evolutionary innovation. Early vertebrates are known to have undergone at least two rounds of whole genome duplications (WGD), with an additional third round in the teleost ancestor ~320 million years ago (MYA). A more recent fourth round of WGD occurred in the ancestor of salmonids ~80-100 MYA, following which speciation preceded complete cytological rediploidization (progressive return to the diploid state), making salmonids an exemplary system to investigate the evolutionary consequences of WGD. We assembled a 1.48 Gb draft assembly of European grayling (Thymallus thymallus), a member of the earliest diverging salmonid lineage, and used this novel genome resource to understand the importance of selective forces on the evolution of genome regulation following WGD.