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

ACOSTA M.C. & A.C. PREMOLI

San Javier, Tucumán

Congreso; XXVII International Meeting of the Willi Hennig Society y VIII Reunión Argentina de Cladística y Biogeografía; 2008

Nothofagus is an important component in discussions of the biogeography 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 interespecific 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 of subgenus Nothofagus. Hybrids among most of these species have been described at a local scale. Four populations of N. obliqua and N. nervosa from 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 (MP) tree (L=70, CI=0.943, RI=0.935) and the DNA chloroplast matrix generated 6 MP trees (L=69, CI=0.957, RI=0.965). Nuclear and chloroplast DNA dataset contained 52 and 58 parsimony informative characters, respectively. Parsimony analyses and Bayesian inference yielded trees with same topologies. Incongruent nuclear and plastid DNA phylogenetic analyses were observed within subgenus Nothofagus. ITS rybotypes showed relationships with the delimited species. Therefore, phylogenetic analysis of ITS sequences is assumed to show the true phylogeny. The monophyly of 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. antartica. Nothofagus pumilio had an early and distinct evolutionary history. In contrast, no relation between chloroplast haplotypes and species were found, but with geographic location instead. Not only do all species share several DNAcp haplotypes, but also that most haplotypes occur in all species within the same area. This is probably due to hybridization and/or introgression due to chloroplast capture events througout 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.