Burgess, Michael , Cushman, Kevin , Doucette, EricThomas , Frye, Christopher , Nelson, Gretchen , Campbell, Christopher .
Pattern and process in Amelanchier (Rosaceae) polyploids.
Polyploidy in Amelanchier, which is coincident with apomixis, creates significant taxonomic complexity. Understanding the pattern and process of polyploidy establishes a foundation for a pragmatic classification. Using flow cytometry, we have detected 430 tetraploids and 58 triploids across a broad taxonomic and geographic sample.Despite extensive sampling, we have only detected two triploid plants in western North America. Preliminary data suggest the occurrence of a pentaploid plant growing with diploids and tetraploids in eastern Pennsylvania. If confirmed this would represent the first report of pentaploidy in the genus. In eastern North America, triploids and tetraploids appear more abundant in northern latitudes but they do extend southward to the 36th parallel north. Using sequence data from ETS, ITS, and a LEAFY gene, allopolyploidy has been detected in 95% of sampled polyploid taxa. The remaining samples, which include A. pallida and A. bartramiana are autopolyploids, the first to be documented in the genus. Polyploids range from recurrently forming allotetraploids, such as A. xNeglecta, to ancient polyploids, such as A. alnifolia and A. cusickii of western North America. The latter harbor sequences from a LEAFY gene that attach to branches deep within the genus. Several such sequences from strongly supported, geographically widespread clades, were presumably retained through apomixis. Polyploids formed via allopolyploidy or hybridization between polyploids can be morphologically indistinguishable from a diploid species. This pattern, which is expected for autoplolyploids, typifies the challenges of interpreting and classifying polyploid diversity in Amelanchier. Flow cytometric screening of seeds from allotetraploids has confirmed earlier findings that apomixis is nearly obligate. This contrasts with diploid species that are nearly obligate sexuals. Apomixis was documented in 83% of triploid seeds, with the remaining being sexual. Analysis of triploid seeds also uncovered four unique pathways for the triploid bridge. Despite expected constraints of 'triploid block', triploids in Amelanchier appear to be important intermediate steps in the formation of tetraploids.
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Systematics and Evolution of Amelanchier (Rosaceae)
1 - University of Pennsylvania, Botany, 100 E. Northwestern Avenue, Philadelphia, PA, 19118
2 - P.O. Box 143, Levant, ME, 04456, USA
3 - University of Maine, Ecology and Environmental Science, Orono, ME, 04469
4 - Maryland Wildlife And Heritage Service, 909 Wye Mills Road, PO Box 68, Wye Mills, MD, 21679, USA
5 - 269 French Street, Apt C, Bangor, ME, 04401, USA
6 - University Of Maine, Department Of Biological Sciences, 261 HITCHNER HALL, ORONO, ME, 04469-5735, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Delaware D/Hyatt
Date: Wednesday, July 11th, 2012
Time: 9:00 AM