Lo, Eugenia , Stefanovic, Sasa , Dickinson, Timothy A. .
Reticulate history and population genetic structure of black-fruited hawthorns (Crataegus; Rosaceae) in the Pacific Northwest.
In North America, many hawthorn species are characterized by polyploidy and the ability to reproduce both sexually and apomictically. However, the origin(s) and population genetic structure of the polyploids are poorly understood. In western North America, Crataegus suksdorfii is known to include diploid sexuals and polyploid apomicts. We used maximum parsimony and statistical parsimony methods to construct trees and networks with nuclear and chloroplast gene regions for population samples of diploid and polyploid C. suksdorfii, and of the closely-related tetraploid C. douglasii. Microsatellite markers were then employed to investigate population structure and compare genetic variability across ploidy levels. Three different pathways of polyploid formation were identified. Triploid individuals of C. suksdorfii from the Cascades were derived independently, in one case, homogeneously by inheriting almost identical nuclear and chloroplast genomes from a diploid progenitor, and in the other case, heterogeneously by merging genomes from diploid C. suksdorfii and tetraploid C. douglasii. Within-population multilocus genotypic variation is the lowest in these triploid populations. Tetraploid individuals are formed via a triploid bridge, involving the backcross of allotriploid offspring with diploid C. suksdorfii parent, followed by gene introgression from sympatric C. douglasii. Within-population multilocus genotypic variation in these tetraploid populations is almost as high as that in the diploid samples. STRUCTURE and AMOVA analyses suggest high interpopulation differentiation and strong genetic structuring in C. suksdorfii as a result of gene flow being limited by ploidy level differences and distance. In contrast, in tetraploid C. douglasii, frequent gene flow among the Pacific Northwest individuals contributes to an appreciable level of genetic diversity within apomictic populations, and demonstrates successful colonization of C. douglasii. Our findings provide new insights into the reticulation history that characterize much of this taxonomically complicated genus and shed light on evolution of woody plants that show heterogeneous ploidy levels and reproductive systems.
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1 - Royal Ontario Museum, Natural History, 100 Queen\'s Park, Toronto, Ontario, M5S 2C6, Canada
2 - University of Toronto at Mississauga, Biology, 3359 Mississauga Rd N, Mississauga, Ontario, L5L1C6, Canada
3 - Royal Ontario Museum, Centre for Biodiversity and Conservation Biology, Royal Ontario Museum 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada
Presentation Type: Poster:Posters for Topics
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM