The oaks of western Eurasia: Traditional classifications and evidence from two nuclear markers

Abstract

Phylogenetic relationships among species of Quercus (oaks) from western Eurasia including the western part of the Himalayas are examined for the first time. Based on ITS and 5S–IGS data three major infrageneric groups are recognized for western Eurasia: the cerroid, iliciod, and roburoid oaks. While individuals of the cerroid and ilicoid groups cluster according to their species, particularly in the 5S–IGS analyses, individuals of species of roburoid oaks do not cluster with exception of Quercus pontica. The Cypriot endemic Quercus alnifolia belongs to the ilicoid oaks, in contrast to traditional views placing it within the cerroid oaks. Based on all ITS data available, the groups identified for western Eurasia can be integrated into a global infrageneric framework for Quercus. The Ilex group is resurrected as a well–defined group that comprises taxa traditionally placed into six subsections of Q. sects. Cerris and Lepidobalanus (white oaks) sensu Camus. Phylogenetic reconstructions suggest two major lineages within Quercus, each consisting of three infrageneric groups. Within the first lineage, the Quercus group (roburoid oaks in western Eurasia) and the Lobatae group evolved by “budding” as is reflected by incomplete lineage sorting, high variability within groups, and low differentiation among groups. The groups of the second lineage, including the Cyclobalanopsis, Cerris (cerroid oaks in western Eurasia), and Ilex (ilicoid oaks in western Eurasia) groups, evolved in a more tree–like fashion.

Evolution of rDNA FISH patterns in the Fagaceae

“…We hypothesize that some of these divergences can be correlated with the different number of rDNA loci present in this group, where different FISH patterns are found: either the same, as in all species of subgenus Quercus and other Cyclobalanopsis species (Chokchaichamnankit et al 2008), or different with a high number of paralogous sites. Moreover, Denk and Grimm (2010), based on ITS and 5S-IGS data, concluded that the Cyclobalanopsis group shares a common ancestor with the Cerris and Ilex groups, and at the same time is closer to other Fagaceae than to the remainder of species of the Quercus genus. Interestingly, these phylogenetic patterns indicate that the Cyclobalanopsis group was isolated, and possibly radiated soon after the initial divergence, separating the two major clades within oaks.…”

An improved method for chloroplast genome sequencing in non-model forest tree species

“…The Fagaceae species are considered as keystone species in forest ecosystem and are important drivers of terrestrial biodiversity. Quercus L., the largest genus in Fagaceae family, comprises ∼400 species; most of the diversity of the genus lies in Central America and Southeast Asia (Denk and Grimm 2010). However, till now, extensive genetic and genomic studies are conducted mainly on less species-rich European oaks (e.g., Kremer and Petit 1993;Kremer et al 2010;Plomion et al 2015).…”

Molecular Organization of the 25S–18S rDNA IGS of Fagus sylvatica and Quercus suber: A Comparative Analysis

“…covering three of the five or six major intrageneric lineages ( Q. faginea, Q. pyrenaica, Q. rubra and Q. suber ) [17], [19], [55], in two Castanea spp. ( C. sativa and C. mollissima ) from different geographic origins, and in Fagus sylvatica .…”

“…More gene types than the number of 35S rDNA loci suggest that different variants occur in the same locus indicating an insufficient homogenization of the IGS. Moreover, in Q. petraea and Q. robur three divergent rDNA clusters have been isolated [30], and intra-individual variability was found in ITS and 5S-IGS [17]. Differences in the number of length variants have been correlated with several traits in wild and cultivated plants and seem to have ecological significance that can respond to selection pressure (revision in [2]).…”

“…Various studies in this family used the variation in the internal transcribed spacers (ITS1 and ITS2) of the 18-5.8-25S rDNA and the 5S rDNA intergenic spacers (5S-IGS) mainly for systematic and phylogenetic purposes [17]–[20]. However, the sequence structure of the NTS and ETSs have only been studied in two very closely related sympatric species: Quercus petraea and Q. robur [8].…”