Weak Geographical Structure of Juniperus sabina (Cupressaceae) Morphology despite Its Discontinuous Range and Genetic Differentiation

Abstract

In Europe, Juniperus sabina L. is a mountainous, rare species that creates small, scattered populations, suggesting their refugial nature. Recently, a new variety of this juniper, J. sabina var. balkanensis R. P. Adams et A. N. Tashev was described based on genetic studies. We expected morphological differentiation among isolated parts of the species range and between varieties, as was the case with other Mediterranean junipers. Cones, seeds and fragments of shoots from a total of 506 individuals were collected from 24 populations in Europe and for comparisons from three populations from Tian Shan. Almost all of the 16 analysed features significantly differentiated among populations and geographical regions as well as between the varieties, although most groups differed from others only in terms of a single feature. The thickness of cones, the width of shoots and the length of seeds were the most important features for differentiation. The geographical structure of the variation of J. sabina was weak, and comparative populations from Tian Shan were clustered with European populations, similar to the findings of a previous study on essential oils. We found slightly different patterns of variation of the two varieties of the species. The little intra-species differentiation could be the result of the long period of contact between nowadays distinct populations and their relatively late separation in the early Holocene.

Soil Requirements, Genetic Diversity and Population History of the Juniperus sabina L. Varieties in Europe and Asia

“…Although the juniper varieties are distinct based on the cpDNA markers, the population structure inferred from the nuclear microsatellites was unclear, since some genetic clusters included geographically distant populations or populations with different ploidy levels. Nevertheless, this outcome was congruent with the previous population structure assessment based on the SNP and SilicoDArT markers [14] and morphological parameters [22]. We suppose that clonal propagation, inbreeding and limited gene flow between populations occupying different mountain ranges contribute to a moderate genetic variation of the J. sabina populations.…”

“…Morphological analyses showed a striking similarity between the KYR individuals and var. sabina from Europe [22]. The morphological differences among J. sabina populations across the vast region from Europe to Kyrgyzstan appear to be primarily shaped by geographical factors rather than taxonomic distinctions.…”

“…The sabina and balkanensis varieties are morphologically indistinguishable [22], but they are genetically distinct respecting chloroplast (cp) DNA and both SilicoDArT and SNP loci obtained by whole-genome sequencing [9,11,14]. The SilicoDArT-and SNPbased analyses revealed relatively low levels of genetic diversity of both varieties, but this investigation involved a small number of individuals per population [14].…”

“…The morphological differences among J. sabina populations across the vast region from Europe to Kyrgyzstan appear to be primarily shaped by geographical factors rather than taxonomic distinctions. Consequently, this leads to a relatively weak geographical pattern in the observed morphological variation [22].…”

“…balkanensis were greater than those found in var. sabina, but the classification of a population into one or another variety failed based on the individual features [22]. It would be worthwhile to study how var.…”