Concordant geographic distribution and extensive hybridization within Nothofagus (subgenus Nothofagus) are reflected in the chloroplast genome

ACOSTA, M.C. & A.C. PREMOLI

CLADISTICS (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 p. 202 - 203

0748-3007

Nothofagus is an important component in discussions of the biogeographical history of the Southern Hemisphere because of its disjunct distribution in Gondwana. The phylogeny of the genus has been investigated using morphology and sequences of chloroplast and nuclear DNA. Nevertheless, the interrelationships among their species remain poorly understood. The objective of this study is to analyze interspecific relationships within of the South American subgenus Nothofagus. We used a spatially explicit sampling design to analyze the extent of hybridization between their species. Leaf material was collected from 32 populations of N. antarctica, N. betuloides, N. dombeyi, N. nitida and N. pumilio (all in the subgenus Nothofagus). Hybrids among most of these species have been described at a local scale. Four populations of N. obliqua and N. nervosa (subgenus Lophozonia) were used as outgroups. The complete internal transcribed spacer (ITS) region, including the 5.8S rRNA gene, and three regions of the chloroplast genome (psbB–psbH, trnL– trnF, trnH–psbA) were amplified. Parsimony analysis was conducted using WINCLADA and NONA, and Bayesian inference was done in MrBayes, both on the separate nuclear and chloroplast datasets. A model of sequence evolution was selected using MrModeltest. Parsimony analyses of the aligned ITS data returned only one most parsimonious tree (MPT; L = 70, CI = 0.943, RI = 0.935) and the DNA chloroplast matrix generated 6 MPTs (L = 69, CI = 0.957, RI = 0.965). The nuclear and chloroplast DNA dataset contained 52 and 58 parsimony informative characters, respectively. The parsimony and Bayesian analyses yielded trees with the same topology. Incongruent nuclear and plastid DNA phylogenetic analyses were observed within the subgenus Nothofagus. ITS ribotypes showed relationships with the delimited species. Therefore, phylogenetic analysis of ITS sequences is assumed to show the true phylogeny. The monophyly of the subgenus Nothofagus is well supported. The evergreen species N. dombeyi and N. betuloides have been recently differentiated, which together with N. nitida are sister to the deciduous N. antarctica. Nothofagus pumilio had an early and distinct evolutionary history. In contrast, chloroplast haplotypes had no obvious relationship to species, but with geographic location instead. Not only do all species share several DNAcp haplotypes, but most haplotypes occur in all species within the same area. This is probably due to hybridization, introgression, and chloroplast capture events throughout the evolutionary history of such ancient taxa. In order to avoid erroneous phylogenetic conclusions both nuclear and chloroplast DNA based studies and comprehensive sampling methods are needed.