Genetic Issues and Pando

Genetic identity of the Pando clone

GenoTypes

In 2008, scientists from the USDA National Forest Genetics Laboratory and Utah State University used a DNA fingerprinting technique to confirm that the Pando clone, originally identified based on morphological traits2, was indeed a single genetic entity1. In other words, this enormous clone at some point in history emerged from a single seed about the size of a flea.

Aspen Seeds

How old is Pando?

It is tempting to use estimates of clonal spread and climate history to estimate the age of Pando (i.e. when the original seed germinated). However, these methods require too many assumptions to make a reasonable data-based estimate. Based simply on size, most scientists guess that Pando may be thousands of years old. Some scientists have explored the use of mutation accumulation (genetic) data to improve age estimates, but to date these data have not led to an age estimate for Pando. Given the rapid turnover of aspen tissue both above- and below-ground, it is unlikely that any tissue remains from the original seedling that established the Pando clone.

Genetic diversity in the stand containing the Pando clone

The Pando clone exists within a larger aspen stand. Although Pando completely dominates this stand spatially, there are other clones within the stand2. In the process of genotyping the Pando clone, USDA and USU scientists discovered that 52 additional clones were identified, most of which were very small (<165 ft/50 m across)5. This very high level of clonal richness was unexpected. Most of these clones were clustered at the edges of the Pando clone, suggesting that they may have arisen from a relatively recent seeding event. This finding, along with a similar pattern found in several other aspen plots in the western U.S.5, was surprising to western forest managers, who previously did not consider seed reproduction to be a significant factor in western aspen regeneration3.

Triploidy

Based on recent genetic work, Pando and many other clones in the western U.S. are triploid, meaning that they have three copies of their genome instead of the usual two copies (diploid)4. Interestingly, the larger clones have a strong tendency to be triploid5, suggesting that triploids have some advantage over diploids. However, triploids may also have particular physiological vulnerabilities (e.g. water stress). Understanding physiological differences between diploid and triploid aspen is a focus of current research at the University of Wisconsin (Lindroth) and Utah State University (Mock).

1DeWoody J, Rowe CA, Hipkins VD, Mock KE (2008) “Pando” lives: molecular genetic evidence of a giant aspen clone in central Utah. Western North American Naturalist, 68, 493-497.

2Kemperman JA, Barnes BV (1976) Clone size in American aspens. Canadian Journal of Botany, 54, 2603-2607.

3Long J, Mock KE (2012) Changing perspectives on regeneration ecology and genetic diversity in western aspen: implications for silviculture. Canadian Journal of Forest Research 42, 2011-2021.

4Mock KE, Callahan CM, Islam-Faridi MN, Rai HS, Sanderson SC, Rowe CA, Ryel RJ, Shaw JD, Madritch MD, Gardner RS, Wolf PG (2012) Widespread triploidy in trembling aspen (Populus tremuloides). PLoS ONE 7(10): e48406.

5Mock KE, Rowe CA, Hooten MB, DeWoody J, Hipkins VD (2008) Clonal dynamics in western North American aspen (Populus tremuloides). Molecular Ecology 17, 4827-4844.

For additional information about this research please contact Dr. Karen Mock, Department of Wildland Resources, Utah State University

karen.mock@usu.edu