The Ecological Evolution of Salmoniformes

The ecological evolution of the order Salmoniformes is analyzed for the first time using the method of historical biogeography and considering the formation of the ecology and reproductive biology of these species in the process of their evolution under planetary climatic and geological changes. As follows from the analysis, the climate cooling in the Cenozoic and the associated change in food supply for Salmoniformes mainly influenced the evolution of their ecology. This process at the Asian coast of the North Pacific began much earlier than at the American coast and was much more intense there. Salmoniformes occupied marine and oceanic feeding grounds, which led to a multifold increase in the abundance of species and to its significant imbalance with the available amount of food in freshwaters. In the Oncorhynchus species, this was manifested as the irreversible reduction in organs and functions and the total mortality of spawners. Because of the timing of reproduction to the spring peak of the food supply for larvae and the increase in the time of egg development in redds during climate cooling, anadromous and semi-anadromous salmoniforms were forced to begin the originally spring spawning earlier and it gradually shifted to winter and then to autumn. Consequently, the onset of the spawning run in rivers also shifted to earlier dates. An analysis of the formation of Atlantic salmon and brown trout ecology has shown that there is no reason to consider fish of autumn and spring–summer runs in the north of their range and fish of winter–spring and autumn runs in the south as seasonal races. These are a single spawning run temporarily interrupted by winter cooling or summer heating of near-shore sea waters and lower reaches of rivers. In the late Pliocene, northern and southern populations of Salmoniformes in the Pacific Ocean were widely and permanently separated by cold. As a result of isolation, these populations have diverged so greatly that they should be considered as separate taxa rather than seasonal races.