Evolution, invasion, admixture and introgression among the Gadids. The Arctic and Polar cod are an outgroup of the Gadids, which are marine fish supporting most important fisheries in the North Atlantic and Pacific. A few millions years ago, an ancestral lineage of Atlantic cod invaded the Pacific Ocean and evolved to become Pacific cod. Slightly later, another invasion of an ancestral Atlantic cod into the Pacific Ocean, evolved to become the walleye pollock shifting its niche by getting genes for adaptation through admixture and introgression from other species. Much later Pacific cod re-invaded the Atlantic Ocean at Western Greenland evolving into Greenland cod, also acquiring genes through introgression. These fish are ecological success stories and their ecological success in turn translates into their ability to support important commercial fisheries. Their ability to invade and expand into new habitats and become ecologically successful may depend on genes acquired through adaptive introgression or hybrid speciation. The ongoing climate warming, Northern hemisphere ice melting, and the opening of the Arctic predict species interchange between the North Pacific and the North Atlantic. This study shows that the potential exists for further hybridization of Pacific, Arctic, and Atlantic species, with unknown consequences for biodiversity. This material relates to a paper that appeared in the March 20th, 2019, issue of Science Advances, published by AAAS. The paper, by E. Árnason at University of Iceland in Reykjavík, Iceland, and colleagues was titled, "Codweb: Whole-genome sequencing uncovers extensive reticulations fueling adaptation among Atlantic, Arctic, and Pacific Gadids."
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