Biodiversity Evolution of a Shrub Betula nana L. Populations in the Urals

Genetic polymorphism of B. nana along the Ural ridge is analyzed based on the variability of trn S -trn G, trn L -trn F, trn S -trn T, trn K1 -trn K2, and mat K1 cpDNA markers with the application of the RFLP method. Specimens of B. pubescens were additionally taken for comparative analysis. The research revealed 12 chlorotypes in B. nana and B. pubescens populations, among which chlorotypes A and B were the most frequent. The Polar Urals populations are characterized by prevailing chlorotype A, significantly decreased genetic polymorphism (He = 0.169), and low divergence (Fst = 0.000–0.050), which are possibly associated with the Pleistocene and Holocene migration processes, the edge effect, and specific ecological conditions of the arctic tundra. The populations of the Middle Urals show prevailing chlorotype B and higher genetic variability (He = 0.296). Reduced gene flow between bog populations of the Middle Urals results in high interpopulation divergence (Gst = 0.701, Nst = 0.764). Shared cpDNA haplotypes and low interspecific differentiation between B. nana and B. pubescens are indicated (Gct = 0.007, Nct = 0.064). Flow cytometry revealed homogeneous DNA content in B. nana and B. pubescens specimen populations (Serebryansky Kamen and Sredneuralsk) with a total 2C DNA content variation range of 0.91–1.09 pg for B. nana and 1.85–2.10 pg for B. pubescens and the absence of triploid hybrids among the studied samples, which suggests a low frequency of occurrence of the latter and, possibly, northern localization of these birch species hybridization zones.