Patterns of genetic variation in leading-edge populations of Quercus robur : genetic patchiness due to family clusters
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ORIGINAL ARTICLE
Patterns of genetic variation in leading-edge populations of Quercus robur: genetic patchiness due to family clusters Pekka Vakkari 1
&
Mari Rusanen 1 & Juha Heikkinen 1 & Tea Huotari 2 & Katri Kärkkäinen 3
Received: 13 January 2020 / Revised: 18 August 2020 / Accepted: 28 August 2020 / Published online: 14 September 2020 # The Author(s) 2020
Abstract The genetic structure of populations at the edge of species distribution is important for species adaptation to environmental changes. Small populations may experience non-random mating and differentiation due to genetic drift but larger populations, too, may have low effective size, e.g., due to the within-population structure. We studied spatial population structure of pedunculate oak, Quercus robur, at the northern edge of the species’ global distribution, where oak populations are experiencing rapid climatic and anthropogenic changes. Using 12 microsatellite markers, we analyzed genetic differentiation of seven small to medium size populations (census sizes 57–305 reproducing trees) and four populations for within-population genetic structures. Genetic differentiation among seven populations was low (Fst = 0.07). We found a strong spatial genetic structure in each of the four populations. Spatial autocorrelation was significant in all populations and its intensity (Sp) was higher than those reported in more southern oak populations. Significant genetic patchiness was revealed by Bayesian structuring and a high amount of spatially aggregated full and half sibs was detected by sibship reconstruction. Meta-analysis of isoenzyme and SSR data extracted from the (GD)2 database suggested northwards decreasing trend in the expected heterozygosity and an effective number of alleles, thus supporting the central-marginal hypothesis in oak populations. We suggest that the fragmented distribution and location of Finnish pedunculate oak populations at the species’ northern margin facilitate the formation of within-population genetic structures. Information on the existence of spatial genetic structures can help conservation managers to design gene conservation activities and to avoid too strong family structures in the sampling of seeds and cuttings for afforestation and tree improvement purposes. Keywords Spatial genetic structure . Relatedness . Kinship reconstruction . Marginal populations
Introduction Genetic variation within populations is crucial for their survival in the changing environment. Populations of forest trees Communicated by F. Gugerli Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11295-020-01465-9) contains supplementary material, which is available to authorized users. * Katri Kärkkäinen [email protected] 1
Natural Resources Institute Finland (Luke), P.O. Box 2, 00791 Helsinki, Finland
2
Department of Agricultural Sciences, University of Helsinki, PO Box 27, Latokartanonkaari 5, FI-00014 Helsinki, Finland
3
Natural Resources Institute Finland (Luke), University of Oulu, Paavo
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