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AOBPreview originally published online on November 10, 2007
Annals of Botany 2008 101(1):145-152; doi:10.1093/aob/mcm271
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Origins and Widespread Distribution of Co-existing Polyploids in Arnica cordifolia (Asteraceae)

Rebecca Hufft Kao*

University of California Santa Cruz, EE Biology, EMS A316, 1156 High St, Santa Cruz, CA 95064, USA

* For correspondence. Present address: Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177, USA. E-mail rhkao{at}lamar.colostate.edu

Received: 4 February 2007    Returned for revision: 15 May 2007    Accepted: 10 September 2007    Published electronically: 12 November 2007

Background and Aims: Polyploidy is a central force structuring genetic diversity in angiosperms, but its ecological significance and modes of origin are not fully understood. This work investigated the patterns of coexistence and molecular relatedness of polyploids in the perennial herb, Arnica cordifolia.

Methods: The local- and broad-scale distributions of cytotypes were analysed using flow cytometry. Samples were collected from both roadside and understorey habitats to test the hypothesis of niche separation between triploids and tetraploids. The nuclear rDNA internal transcribed spacer (ITS) and plastid rpl16 spacer, trnL intron plus trnL-trnF spacer and trnK 3' intron regions were sequenced.

Key Results: Broad-scale sampling established that both triploids and tetraploids were common throughout the range of the species, pentaploids were rare, and diploids were not found. Local-scale sampling revealed coexistence of both triploids and tetraploids within the majority of sites. Triploids and tetraploids were equally represented in the understorey and roadside habitat. Triploids were more variable than tetraploids, but both cytotypes shared polymorphisms in ITS.

Conclusions: Coexistence of cytotypes appears to be the norm in A. cordifolia, but habitat differentiation (roadside vs. understorey) is not supported as a coexistence mechanism. Molecular analyses supported multiple events creating triploids but revealed a lack of variation in the tetraploids. Additionally, sequence polymorphisms in ITS suggested a hybridization event prior to polyploidization.

Key words: Apomixis, Arnica cordifolia, flow cytometry, habitat differentiation, minority cytotype exclusion theory, polyploidy


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