Molecular phylogeography of the Andean alpine plant, Gunnera magellanica

Abstract:

To clarify the evolutionary history of Gunnera magellanica (Gunneraceae), an alpine plant of the Andes mountains, we performed molecular phylogeographic analyses based on the sequences of an internal transcribed spacer (ITS) of nuclear ribosomal DNA and four non-coding regions (trnH-psbA, trnL-trnF, atpB-rbcL, rpl16 intron) of chloroplast DNA. We investigated 3, 4, 4 and 11 populations in, Ecuador, Bolivia, Argentina, and Chile, respectively, and detected six ITS genotypes (Types A–F) in G. magellanica. Five genotypes (Types A–E) were observed in the northern Andes population (Ecuador and Bolivia); only one ITS genotype (Type F) was observed in the southern Andes population (Chile and Argentina). Phylogenetic analyses showed that the ITS genotypes of the northern and southern Andes populations form different clades with high bootstrap probability. Furthermore, network analysis, analysis of molecular variance, and spatial analysis of molecular variance showed that there were two major clusters (the northern and southern Andes populations) in this species. Furthermore, in chloroplast DNA analysis, three major clades (northern Andes, Chillan, and southern Andes) were inferred from phylogenetic analyses using four non-coding regions, a finding that was supported by the above three types of analysis. The Chillan clade is the northernmost population in the southern Andes populations. With the exception of the Chillan clade (Chillan population), results of nuclear DNA and chloroplast DNA analyses were consistent. Both markers showed that the northern and southern Andes populations of G. magellanica were genetically different from each other. This type of clear phylogeographical structure was supported by PERMUT analysis according to Pons & Petit (1995, 1996). Moreover, based on our preliminary estimation that is based on the ITS sequences, the northern and southern Andes clades diverged ~0.63–3 million years ago, during a period of upheaval in the Andes. This suggests that the populations of G. magellanica that were distributed along the Andes have been divided into the two local populations of the northern and southern Andes during the uplift of the Andes.