AOBPreview originally published online on January 5, 2004
Annals of Botany 93: 189-200, 2004
© 2004 Annals of Botany Company
Fine-scale Geographical Structure, Intra-individual Polymorphism and Recombination in Nuclear Ribosomal Internal Transcribed Spacers in Armeria (Plumbaginaceae)
1 Real Jardín Botánico (CSIC), Plaza de Murillo 2, E-28014 Madrid, Spain
* For correspondence. E-mail nieto{at}ma-rjb.csic.es
Received: 24 June 2003;; Returned for revision: 6 October 2003; Accepted: 29 October 2003: Published electronically: 5 January 2004
• Background and Aims Isolation and drift are the main causes for geographic structure of molecular variation. In contrast, the one found in a previous survey in Armeria (Plumbaginaceae) for nuclear ribosomal ITS multicopy regions was species-independent and has been hypothesized to be due to extensive gene-flow and biased concerted evolution. Since this was inferred from a genus-level phylogenetic analysis, the aim of this study was to check for the occurrence of such structure and the validity of the proposed model at a local scale, in a southern Spanish massif (Sierra Nevada), as well as to examine the evolutionary implications at the organism level.
• Methods In addition to 117 sequences of direct PCR products from genomic DNA, 50 sequences of PCR products from cloned DNA were obtained to analyse cases of intragenomic polymorphisms for the ITS regions.
• Key Results Sequence data confirm the occurrence of a species-independent structure at a local scale and reveal insights through the analysis of contact areas between different ITS copies (ribotypes). A comparison between cloned and direct sequences (a) confirms that, within these contact areas, ITS copies co-occur both in different individuals and within single genomes; and (b) reveals recombination between different copies.
• Conclusions This study supports the utility of direct sequences for detecting intra-individual polymorphism and for partially inferring the ITS copies involved, given previous knowledge of the variability. The main evolutionary implication at the organism level is that gene-flow and concerted evolution shape the geographic structure of ITS variation.
Key words: Armeria, nuclear ribosomal ITS, intragenomic polymorphism, recombination, geographical structure, gene-flow, biased concerted evolution.
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