Phylogeny ofPopulus(Salicaceae) based on nucleotide sequences of chloroplast TRNT‐TRNF region and nuclear rDNA

Abstract

The species of the genus Populus, collectively known as poplars, are widely distributed over the northern hemisphere and well known for their ecological, economical, and evolutionary importance. The extensive interspecific hybridization and high morphological diversity in this group pose difficulties in identifying taxonomic units for comparative evolutionary studies and systematics. To understand the evolutionary relationships among poplars and to provide a framework for biosystematic classification, we reconstructed a phylogeny of the genus Populus based on nucleotide sequences of three noncoding regions of the chloroplast DNA (intron of trnL and intergenic regions of trnT-trnL and trnL-trnF) and ITS1 and ITS2 of the nuclear rDNA. The resulting phylogenetic trees showed polyphyletic relationships among species in the sections Tacamahaca and Aigeiros. Based on chloroplast DNA sequence data, P. nigra had a close affinity to species of section Populus, whereas nuclear DNA sequence data suggested a close relationship between P. nigra and species of the section Aigeiros, suggesting a possible hybrid origin for P. nigra. Similarly, the chloroplast DNA sequences of P. tristis and P. szechuanica were similar to that of the species of section Aigeiros, while the nuclear sequences revealed a close affinity to species of the section Tacamahaca, suggesting a hybrid origin for these two Asiatic balsam poplars. The incongruence between phylogenetic trees based on nuclear- and chloroplast-DNA sequence data suggests a reticulate evolution in the genus Populus.

Genomic Admixture Analysis in European Populus spp. Reveals Unexpected Patterns of Reproductive Isolation and Mating

“…Ancestral polymorphism is an unlikely explanation for allele sharing at the weakly differentiated loci seen in Figure 2. These species diverged at least several million years ago (Stettler et al 1996), and P. alba and P. tremula are not even sister species in most molecular phylogenetic analyses of the genus (Hamzeh and Dayanandan 2004). Accordingly, allele frequency differentials between these taxa often reach values of 0.90 or higher (Table 2; Table S3).…”

Mapping shape quantitative trait loci using a radius-centroid-contour model

“…tibetica. Belonging to the Tacamahaca section, P. szechuanica is naturally distributed throughout the Tibet Plateau, growing in mountains at an altitude of 1100 À4600 m, over a wide range of regions in Gansu, Shaanxi, Sichuan, Xizang and Yunnan Provinces of China (Hamzeh and Dayanandan, 2004). The wide ecological adaptation of this species, along with its pronounced variation in leaf size and shape (Figure 1), makes this species ideal to study the genetic variation of leaf morphology using molecular markers.…”

“…southwestern China (Hamzeh and Dayanandan, 2004), providing an ideal model system to study the genetics of leaf morphology and its relationship with ecological adaptations. Interestingly, we detected a number of shape QTLs associated with microsatellite markers by shape mapping.…”

Local Selection Across a Latitudinal Gradient Shapes Nucleotide Diversity in Balsam Poplar, Populus balsamifera L

“…In contrast, the phytochromes in P. balsamifera (this study) show low nucleotide diversity and little evidence of positive selection (Table S4 and Figure 2), nor do phytochrome genes cosegregate with bud set QTL in Populus trichocarpa · P. deltoides mapping populations (Chen et al 2002;Rohde et al 2010). Although congenerics, P. balsamifera and P. tremula, are geographically isolated and estimated to have last shared a common ancestor 40 million years ago (Hamzeh and Dayanandan 2004); thus they have presumably migrated and adapted to northern latitude environments independently. The difference in selection on phenology genes suggests that despite showing convergent phenotypic clines in bud set with latitude, these two poplar species differ in the genetic basis of local adaptation.…”