Chloroplast DNA Variation and Phylogeography of Pedunculate Oak Quercus robur L. in the Eastern Part of the Range

Abstract

Chloroplast DNA variation was investigated in 42 populations of pedunculate oak, Quercus robur L., in the European part of Russia, Belarus, Poland, Ukraine, the Urals, and the Caucasus. Restriction analysis and sequencing, as well as chloroplast DNA microsatellite loci (cpSSR), were used as genetic markers. For successful amplification and sequencing, new oak-specific primers were designed. For the first time for Q. robur, nucleotide sequences of three fragments (psaA-trnS, psbC-trnD, and trnT-trnF) were obtained with the determination of phylogenetic relationships among 13 identified haplotypes. In the eastern part of the range, several divergent chloroplast DNA lineages were identified. The haplotype groups were characterized by a nonrandom geographic distribution, which probably reflected the history of oak colonization in these regions. Sharp population differentiation in terms of haplotype composition and the level of variation was revealed. Specifically, in the eastern part of the Russian Plain and in the Urals, two haplotypes are widespread, which are disappearing in the west (Northwestern Russia, Belarus, Poland, and Western Ukraine), where nine haplotypes are found that are absent in east. Geographic structure of chloroplast DNA variation in pedunculate oak from Eastern Europe is similar to that in small-leaved lime (Semerikova et al., 2020), another representative of European temperate forests, in which, like in oak in this part of the range, sharp differences between western and eastern populations were observed. It seems likely that this is the result of postglacial colonization by both species from different, long isolated refugia, some of which were located in the east of the studied areas. In the Urals, parallel differentiation of oak and lime between the southern part (Ural River and Belaya River basins) and more northern regions (Ufa River basin and Middle Urals) was revealed, which can be explained by different historical colonization patterns of these regions by broad-leaved vegetation.