Widespread Triploidy in Western North American Aspen (Populus tremuloides)

• Published in: PloS one Vol. 7; no. 10; p. e48406
• Main Authors: Mock, Karen E, Callahan, Colin M, Islam-Faridi, M. Nurul, Shaw, John D, Rai, Hardeep S, Sanderson, Stewart C, Rowe, Carol A, Ryel, Ronald J, Madritch, Michael D, Gardner, Richard S, Wolf, Paul G, Niedz, Randall P
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 31-10-2012; Public Library of Science (PLoS)
• Subjects: Agriculture; Aneuploidy; Biology; Cavitation; Chromosomes; climate; Cytology; Cytometry; cytotypes; Drought; Ecological effects; Ecological monitoring; Ecological studies; Ecology; Fertility; Flow cytometry; Gene expression; Genomes; Genotyping; Glacial periods; Incidence; Laboratories; Landscape; landscapes; latitude; loci; microsatellite repeats; Microsatellite Repeats - genetics; Microsatellites; mortality; North America; perennials; Physiological effects; Physiology; Polyploidy; Populus - genetics; Populus nigra; Populus tremuloides; Regional climates; Speciation; Species; Tetraploidy; Triploidy; variance; North America; United States > US; Utah
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0048406

We document high rates of triploidy in aspen (Populus tremuloides) across the western USA (up to 69% of genets), and ask whether the incidence of triploidy across the species range corresponds with latitude, glacial history (as has been documented in other species), climate, or regional variance in clone size. Using a combination of microsatellite genotyping, flow cytometry, and cytology, we demonstrate that triploidy is highest in unglaciated, drought-prone regions of North America, where the largest clone sizes have been reported for this species. While we cannot completely rule out a low incidence of undetected aneuploidy, tetraploidy or duplicated loci, our evidence suggests that these phenomena are unlikely to be significant contributors to our observed patterns. We suggest that the distribution of triploid aspen is due to a positive synergy between triploidy and ecological factors driving clonality. Although triploids are expected to have low fertility, they are hypothesized to be an evolutionary link to sexual tetraploidy. Thus, interactions between clonality and polyploidy may be a broadly important component of geographic speciation patterns in perennial plants. Further, cytotypes are expected to show physiological and structural differences which may influence susceptibility to ecological factors such as drought, and we suggest that cytotype may be a significant and previously overlooked factor in recent patterns of high aspen mortality in the southwestern portion of the species range. Finally, triploidy should be carefully considered as a source of variance in genomic and ecological studies of aspen, particularly in western U.S. landscapes.