Polytopic speciation of the plague microbe Yersinia pestis as the cause of the triсhotomy in the geographic populations of Mongolian marmot-tarbagan (Marmota sibirica)
Modern phylogeny of the plague pathogen (<i>Yersinia pestis</i>), built on using molecular-genetic (MG) methods, postulates the emergence in the Middle Ages, between the first (6–8<sup>th</sup> century) and the second (14–18<sup>th</sup> century) pandemics, of a unique polytomy (trichotomy) – simultaneous “explosive” (“Big Bang”) formation in Central Asia in the populations of Mongolian marmot-tarbagan (<i>Marmota sibirica</i>) of three new phylogenetic lines of <i>Y. pestis</i> (genovariants 2.ANT3, 3.ANT2, and 4.ANT1), emanating from the basal hypothetical branch 0. These genovariants founded numerous natural plague foci in populations of Mongolian marmot during very short historical time, about 1000 ± 400 y.a. The MG approach does not offer an adequate explanation of this declared questionable natural retro-phenomenon. As an alternative, environmental data show the formation of the specified polytomy in the process of the origin of polytopic genovariants 2.ANT3, 3.ANT2 and 4.ANT1 at the turn of the Pleistocene and the Holocene in the three geographical populations of the Mongolian marmot. Further adaptive radiation and microevolution of the genovariants followed separate paths and were accompanied by the parallel formation of numerous derivative genovariants, characterizing the modern natural plague foci in Asia. The dilemma of the emergence of polytomy on the phylogenetic tree of <i>Y. pestis</i> requires studying based on both approaches, MG and environmental.