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Kildin cod is a small landlocked population of Atlantic cod reproductively isolated from marine counterparts for around 1500-2000 years. The Kildin cod lives in a shallow meromictic lake in the five-meter intermediate layer of water with sharp gradients of oxygen and salinity. The cod had an effective population size of around one hundred individuals and evolved unique physiological, morphological and behavioral features. The marine Atlantic cod has two ecologically distinct forms: the stationary (coastal) and migratory (deep-water) ecotypes that differ in migratory behavior and habitat preferences (the depth, oxygen content, salinity and temperature). To understand the origin and genetic properties of Kildin cod, we scrutinized genomic regions associated with the cod ecotypes differentiation (LG1, LG2, and LG7) and found out that Kildin cod’s regions LG2 and LG7 were fixed with the migratory variants, whereas polymorphic LG1 had a higher frequency of the stationary variant, that could be explained by the possible strong genetic drift. The lake cod investigated had four times lesser genome diversity than marine population. Our finding suggests that Kildin cod originated from the migratory ecotype of the marine cod.
In this work we compared landlocked Kildin cod, a small isolated population of Gadus morhua from meromictic Lake Mogilnoe, with two described cod ecotypes - migratory and stationary. Perhaps it would be additional changes, and here attached raster small versions of images, then we going to sent it to the peer-reviewed journal.