Abstract
The aim of this study is to determine the genetic variability and differentiation among populations of pedunculate oak (Quercus robur) at the eastern margin of the species distribution range. We applied new set of 95 geographically informative nuclear SNP (single nucleotide polymorphism) loci developed using Double Digest Restriction Site Associated DNA (ddRAD), a new generation DNA sequencing technology. The study area is located in the basins of the Volga River and its two main tributaries, Kama and Belaya. Despite the strong reduction and fragmentation of pedunculate oak forests over the last several centuries and comparatively small sizes of present stands, a relatively similar genetic diversity of seven populations was observed (on average, allelic diversity υа = 1.472–1.603, observed heterozygosity HO = 0.305–0.358, expected heterozygosity HE = 0.272–0.343). The genetic distances between populations vary between 0.102 and 0.170 (on average, d0 = 0.128). We have identified the absence of a spatial genetic structure and the existence of genetically peculiar populations in the territory studied. The genetic distances of Gregorius between populations vary between 0.102 and 0.170 (on average, d0 = 0.128). Genetic differentiation among populations was statistically significant with a mean of the fixation index FST of 0.075. Populations from the Privolzhye Upplands and from northern parts of the study area make the most contribution to overall inter-population differentiation (d0 = 0.137). No significant differences exist among the samples at lowlands along the Volga river (d0 = 0.110). It was concluded that the multiplicity and different ages of local populations and the complexity of migration routes of the pedunculate oak from Pleistocene refugia and secondary Holocene shelters can cause this phenomenon.
Highlights
The pedunculate oak (Quercus robur L.) is one of the most common European broad-leaved tree species and of considerable ecological and economic significance (Ducousso and Bordacs 2004)
This paper provides results on levels of genetic diversity and differentiation among populations of pedunculate oak on its eastern range using a new set of 95 SNP loci developed using Double Digest Restriction Site Associated DNA, a new generation DNA sequencing technology (Peterson et al 2012)
We considered two main questions: (1) How different are the levels of genetic diversity in populations of the species on its eastern range after long periods of reduction and fragmentation? (2) How does the spatial and genetic structure of pedunculate oak populations in this area correspond to available paleogeographic data and investigations of morphological traits?
Summary
The pedunculate oak (Quercus robur L.) is one of the most common European broad-leaved tree species and of considerable ecological and economic significance (Ducousso and Bordacs 2004). Population diversity and differentiation of the species, gene flow, mating system, the phylogeography and impact of postglacial re-colonization and human activities on the gene pool has been studied extensively over the western part of its range using various modern gene markers (König et al 2002; Petit et al 2002a; Lepoittevin et al 2015; Leroy et al 2020). Genetic studies can be useful for estimating the effect of forest fragmentation on the genetic pool of pedunculate oak populations in changed landscapes
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