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Introduction of the Baikal Seal (Pusa sibirica Gm.) to Lake Baikal and Current Threats to the Population due to Climate Change: A Review. 1. Introduction of the Baikal Seal in the Lake Baikal: Family Ties, Time and Migration

In communication 1, an attempt was made to link the literature data available today on the phylogenetic position of the Baikal seal (Pusa sibirica Gm.) Among the true northern seals (Phocina), the place and time of the origin of its ancestors. Hypotheses about possible ways of penetration of the ancestral form into the lake are critically discussed. Baikal from different sea basins and at different geological times. It is concluded that there is no unequivocal answer to the question about the roots of the Baikal seal (and, therefore, about the ways and time of penetration of its ancestor into Baikal). The ancestral form of the Baikal seal could live in the seas of the Arctic Ocean (Ringed seal Pusa hispida), and in the reservoirs of Paratethys (Caspian seal Pusa caspica), and in the seas of the Far East (Pusa hispida/akiba or Phoca largha). The hypothesis about the relationship of the seal with the ringed seal (Pusa hispida Schreber) is supported and a conclusion is made about the greater probability of the migration of the seal ancestors to Lake Baikal from the Arctic Seas (not earlier than the Pleistocene) using periglacial lakes as intermediate refugia from the advancing ice. The ancestors of the Baikal seal must have had ready-made adaptation mechanisms to the ice conditions of their habitat, which it retained even when living in intermediate reservoirs along the migration routes. It is assumed that the initial number of animals that ended up in Baikal was small (several thousand individuals), and the further evolution of the species took place in an allopatric way. By the time the ancestors of the Baikal seal settled in Baikal, the lake was already a deep-water and cold-water vast reservoir, which it became not earlier than the Pleistocene. The invasion directly into Baikal could have occurred either through the Angara-Yenisei system (subject to an "early" scenario for the emergence of the modern drain), or through the system of the Lena River on glacial lakes in the Vitim River basin and along the Barguzin depression (along the river or bay).