SummaryDespite the large body of research devoted to understanding the role of Quaternary glacial cycles in the genetic divergence of European trees, the differential contribution of geographic isolation and/or environmental adaptation in creating population genetic divergence remains unexplored. In this study, we used a long-lived tree (Taxus baccata) as a model species to investigate the impact of Quaternary climatic changes on genetic diversity via neutral (isolation-by-distance) and selective (isolation-by-adaptation) processes.We applied approximate Bayesian computation to genetic data to infer its demographic history, and combined this information with past and present climatic data to assess the role of environment and geography in the observed patterns of genetic structure.We found evidence that yew colonized Europe from the East, and that European samples diverged into two groups (Western, Eastern) at the beginning of the Quaternary glaciations, c. 2.2 Myr before present. Apart from the expected effects of geographical isolation during glacials, we discovered a significant role of environmental adaptation during interglacials at the origin of genetic divergence between both groups. This process may be common in other organisms, providing new research lines to explore the effect of Quaternary climatic factors on present-day patterns of genetic diversity.

Genetic exchange between divergent lineages of silver fir (Abies alba Mill.) was studied in the Ukrainian Carpathians where two expanding populations originating from different glacial refugia meet. The study included 33 silver fir populations from Ukraine, Romania and Slovakia which were investigated using the maternally inherited mitochondrial nad5-4 marker and biparentally inherited nuclear microsatellites. The boundary between mitochondrial lineages is very sharp; only six populations containing a mixture of different haplotypes were found. Bayesian analysis of population structure based on seven nSSR loci revealed the existence of two clusters which coincided fairly well with mitochondrial lineages. Both haplotype frequencies and proportions of clusters identified by the Bayesian analysis exhibited a clinal transition over the contact zone, with cline widths of 17.6 km for mitochondrial haplotype frequencies (reflecting gene flow by seeds) and 119.6 km for Bayesian clusters based on nSSR (reflecting gene flow by pollen). Allelic richness and gene diversity differ significantly between mitochondrial lineages, the Balkan group being more variable, but an increase in gene diversity towards the boundary between lineages was observed only within the Balkan lineage. The observed patterns are suggested to reflect the postglacial colonization and historical gene flow. They demonstrated that in silver fir as a wind-dispersed species, the colonization front is quite continuous, and the survival of migrant seeds in already established populations is low. The relative contribution of pollen-mediated gene flow to genetic exchange between divergent lineages associated with glacial refugia is much higher than in the case of seeds, but pollen dispersal distance is lower than suggested by earlier studies.

No abstract

Responses of Norway spruce populations to climatic transfer, in terms of growth and survival, were analyzed on the basis of a provenance experiment derived from the international provenance test IUFRO 1964IUFRO /1968. The experiment comprises a series of five trial plots situated at contrasting elevations ranging from 484 to 1,275 m a.s.l., with 11 provenances represented at all trial plots that were used for the analysis. Transfer rates were defined as differences in altitudes or climatic variables between the site of plantation and the site of origin. Optimal transfer rates and optimal climates for individual provenances were derived from quadratic response functions. Spruce provenances generally responded positively by height and volume growth to transfer into lower altitudes, i.e., warmer conditions with less precipitations. The analysis at the level of provenances showed that optimal transfer rates were consistently negatively correlated with the underlying environmental variables and optimal climates were consequently nearly the same for all provenances irrespective of the response traits and ecodistance variables. Stability indices based on joint regression analysis indicate that provenances from higher altitudes, colder and wetter climates tend to be more stable, whereas provenances from lower altitudes, drier and warmer sites are more responsive to site quality. However, the differences in the stability are small and stability indices were generally close to 1. The results indicate that populations in different climates remain adapted to a common optimum and the extent of local adaptation is quite limited. Possible explanations of this observation are briefly discussed.

The eastern‐Mediterranean Abies taxa, which include both widely distributed species and taxa with minuscule ranges, represent a good model to study the impacts of range size and fragmentation on the levels of genetic diversity and differentiation. To assess the patterns of genetic diversity and phylogenetic relationships among eastern‐Mediterranean Abies taxa, genetic variation was assessed by eight nuclear microsatellite loci in 52 populations of Abies taxa with a focus on those distributed in Turkey and the Caucasus. Both at the population and the taxon level, the subspecies or regional populations of Abies nordmanniana s.l. exhibited generally higher allelic richness, private allelic richness, and expected heterozygosity compared with Abies cilicica s.l. Results of both the structure analysis and distance‐based approaches showed a strong differentiation of the two A. cilicica subspecies from the rest as well as from each other, whereas the subspecies of A. nordmanniana were distinct but less differentiated. ABC simulations were run for a set of scenarios of phylogeny and past demographic changes. For A. ×olcayana, the simulation gave a poor support for the hypothesis of being a taxon resulting from a past hybridization, the same is true for Abies equi‐trojani: both they represent evolutionary branches of Abies bornmuelleriana.