Abstract
The Caucasus region is one of the 25 global biodiversity hotspots and constitutes a shelter area for Neogene relict species as well as a center of ongoing radiation. In order to elucidate the taxonomic identity, divergence patterns, and evolutionary history of the largely widespread Georgian durmast oak (Quercus petraea subsp. iberica), we examined leaf morphology and chloroplast DNA (cpDNA) (trnH-psbA, trnK-matK) sequence variation across its South Caucasian range. Six other oak taxa distributed throughout Georgia were included in the dataset and used for comparison. Evidence for differentiation in both sets of traits was found. Populations represented by different taxa from ecologically equivalent areas showed common morphological features and genetic structures. Molecular analysis clearly indicated the presence of two major haplotype lineages (West Caucasian vs. East Caucasian zonation type) and suggested a maternal lineage diversification of Q. petraea subsp. iberica in the Late Miocene, as a likely result of complex patterns associated with major orogenic and climatic changes. The Quaternary glacial oscillations resulted in a number of less common, derived haplotypes. Based on mismatch distribution analysis and neutrality tests, we found no evidence of demographic expansion for the populations from the West and East Caucasian zonation types. The two Caucasian provinces therefore acted as important shelter/diversification areas and as a lineage crossroad for the Georgian oaks. Close intra- and interspecific cpDNA relationships shared with other oaks from bordering countries support the relevant role played by the Colchis region as a primary refugium for the European temperate forest species.
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Data archiving statement
All sequence data generated as part of this study are available on GenBank (http://www.ncbi.nlm.nih.gov/genbank/) under accession numbers LT718008–LT718100 and LT718101–LT718193. All other relevant information and data are included in the paper and its Supplementary Files.
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This work was supported by the Erasmus Mundus Action II ALRAKIS (Lot 7, No. 20112577).
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Fig. S1
Map of Georgia with distribution of seven Caucasian oak taxa according to herbarium data from Institute of Botany, Ilia State University, Tbilisi, Georgia. Protection of lowlands from the northern cold air masses (by the Greater Caucasus), from dry and hot southern air masses (by the Lesser Caucasus), and proximity to the Black Sea created suitable conditions for the development of thermophilous and humid subtropical forests in the western part of the country. In contrast, the more continental climate of middle- and high-mountain zones and protection from western humid air masses by the Likhi mountain chain allowed the distribution of more continental, moderately thermophilous and relatively more frost-resistant coniferous and broad-leaved deciduous forests in both zones. Blue triangles = Q. petraea subsp. iberica, light blue squares = Q. petraea subsp. dshorochensis, yellow circles = Q. macranthera, red triangles = Q. robur subsp. imeretina, green squares = Q. robur subsp. pedunculiflora, grey triangles = Q. hartwissiana, violet squares = Q. pontica. (GIF 2706 kb)
Table S2
Eigenvalues, percentages of explained variance, cumulative percentage of explained variance, contribution of the variables to the first three principal components and communality (extraction coefficient) values of each leaf character in 6 Caucasian oak taxa. (DOCX 14 kb)
Table S3
TrnK-matK and trnH-psbA sequences downloaded from NCBI and used in the molecular analysis. (DOCX 14 kb)
Table S4
Nucleotide variation and relative frequency of 13 cpDNA haplotypes of Georgian oak taxa combined with East European-West Asian oak samples (N = 108). (DOCX 14 kb)
File S5A
Goodness-of-fit test and additional information of the BEAST analysis. (XLSX 10325 kb)
File S5B
BEAST log file output. (PARTIAL 963 kb)
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Ekhvaia, J., Simeone, M.C., Silakadze, N. et al. Morphological diversity and phylogeography of the Georgian durmast oak (Q. petraea subsp. iberica) and related Caucasian oak species in Georgia (South Caucasus). Tree Genetics & Genomes 14, 17 (2018). https://doi.org/10.1007/s11295-018-1232-6
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DOI: https://doi.org/10.1007/s11295-018-1232-6