AOBPreview originally published online on February 19, 2008
Annals of Botany 2008 101(7):909-918; doi:10.1093/aob/mcn023
Karyotype Diversification and Evolution in Diploid and Polyploid South American Hypochaeris (Asteraceae) Inferred from rDNA Localization and Genetic Fingerprint Data
1 Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
2 Departamento de Biología Vegetal y Ecología (Botánica), Facultad de Biología, Universidad de Sevilla, Avenida Reina Mercedes, 41080 Sevilla, Spain
3 Department of Biogeography and Botanical Garden, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
4 Department of Plant Sciences, Cambridge University, Downing Street, Cambridge CB2 3EA, UK
* For correspondence. E-mail hanna.schneeweiss{at}univie.ac.at
Received: 20 November 2007 Returned for revision: 11 January 2008 Accepted: 21 January 2008 Published electronically: 19 February 2008
Background and Aims: Changes in chromosome structure and number play an important role in plant evolution. A system well-suited to studying different modes of chromosome evolution is the genus Hypochaeris (Asteraceae) with its centre of species' diversity in South America. All South American species uniformly have a chromosome base number of x = 4 combined with variation in rDNA number and distribution, and a high frequency of polyploidy. The aim of this paper is to assess directions and mechanisms of karyotype evolution in South American species by interpreting both newly obtained and previous data concerning rDNA localization in a phylogenetic context.
Methods: Eleven Hypochaeris species from 18 populations were studied using fluorescence in situ hybridization (FISH) with 35S and 5S rDNA probes. A phylogenetic framework was established from neighbour-net analysis of amplified fragment length polymorphism (AFLP) fingerprint data.
Key Results: A single 5S rDNA locus is invariably found on the short arm of chromosome 2. Using 35S rDNA loci, based on number (one or two) and localization (interstitial on the long arm of chromosome 2, but sometimes lacking, and terminal or interstitial on the short arm of chromosome 3, only very rarely lacking), seven karyotype groups can be distinguished; five of these include polyploids. Karyotype groups with more than one species do not form monophyletic groups.
Conclusions: Early evolution of Hypochaeris in South America was characterized by considerable karyotype differentiation resulting from independent derivations from an ancestral karyotype. There was marked diversification with respect to the position and evolution of the 35S rDNA locus on chromosome 3, probably involving inversions and/or transpositions, and on chromosome 2 (rarely 3) concerning inactivation and loss. Among these different karyotype assemblages, the apargioides group and its derivatives constitute by far the majority of species.
Key words: Asteraceae, fluorescence in situ hybridization, Hypochaeris, karyotype evolution, polyploidy, rDNA, South America
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