Wheeler, Erica J , Hawryzki, Allan R , Allen, Geraldine A. .
Evolution and phylogeography of polyploidy in the slim-leaf onion (Allium amplectens).
THE slim-leaf onion occurs from central California, where it is widespread and locally common, to British Columbia, where it is restricted to the south-east coast of Vancouver Island and is considered a species at risk. In 1940, Albert Levan reported mixed and homogenous populations of triploid and tetraploid plants inferred from comparative studies of pollen morphology; rare diploids were also inferred, but never confirmed. A preponderance of mixed populations suggests that polyploidization is a dynamic, ongoing process in this species. To investigate the distribution and evolution of chromosomal and genetic variation, we combined cytogenetic surveys with an intraspecific phylogenetic analysis based on the chloroplast trnT-L intergenic spacer in fifty populations of A. amplectens. We found that diploids were the rarest cytotype (10%), followed by triploids (40%) and tetraploids (50%). Mixed ploidy occurred in one third of CA populations but was not detected elsewhere. Chromosomal and genetic variation decreased with increasing latitude, reflecting patterns of post-glacial colonization found in many other North American plant taxa. In particular, the prevalence of genetically homogenous triploid populations in British Columbia implies strong founder effects and also suggests that asexual seed production may confer selective advantage at the northern range limit. We detected six transitions between ploidy levels including within clades, within haplotypes and within populations. We speculate that recurrent polyploidization in A. amplectens may be due to the viability, fitness and persistence of triploids, which provide a “triploid bridge” to tetraploid establishment.
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1 - University of Victoria, Department of Biology, P.O. Box 3020 STN CSC, Victoria, British Columbia, V8W 3N5, Canada
2 - Malaspina University College, Department of Biology, 900 Fifth Street, Nanaimo, British Columbia, V8R 5S5, Canada
western North America.
Presentation Type: Oral Paper:Papers for Topics
Location: 134/Performing Arts Center
Date: Wednesday, August 2nd, 2006
Time: 10:15 AM