Persistent nuclear ribosomal DNA sequence polymorphism in the <i>Amelanchier</i> agamic complex (Rosaceae)

TitlePersistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae)
Publication TypeJournal Article
Year of Publication1997
AuthorsCampbell CS, Wojciechowski MF, Baldwin BG, Alice LA, Donoghue MJ
JournalMolecular Biology and Evolution
Pagination81 - 90
KeywordsBase Sequence, Cloning, Crosses, DNA, Evolution, Genetic, hybridization, Molecular, Molecular Sequence Data, phylogeny, Plant/*genetics, Plants/*genetics, Plants/classification, Polymorphism, Polyploidy, Ribosomal/*genetics, Species Specificity

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa