Aspen Genetics Lab

One of the unique science education opportunities with the Biodiversity Institute includes an aspen genetics lab.  This lab was created and conducted through a partnership between the Biodiversity Institute and Kim Parfitt, an AP Biology teacher at Central High School in Cheyenne.

This project synthesized:

• field observation, hypothesis development, and data collection,
• classroom study of molecular genetics,
• lab-based methods using high tech-facilities to test hypotheses,
• data analysis and scientific write-up of the methods, results and conclusions.

This project is replicable in other classrooms in Wyoming!  If you're interested in getting your class involved in a similar research program, contact Biodiversity Institute Associate Director Dorothy Tuthill (dtuthill@uwyo.edu, 307-766-6279) to coordinate.

Time requirement: This project involves one day of field work, one day of lab work at the Berry Center, one to two days of additional lab work in the classroom or at the Berry Center, and data analysis and write-up in the classroom.  It is appropriate for advanced high school biology students, and is most successful if integrated into a unit on molecular genetics.

Contact Dorothy Tuthill, dtuthill@uwyo.edu, 307-766-6279 for more information.

Above: Students use Berry Center facilities to extract DNA from their aspen leaf samples

Outdoor Education Case Study: Aspen Genetics

Quaking aspen (Populus tremuloides) is the most broadly distributed tree species in North America, extending from the mountains of Mexico, up the Rocky Mountains and into Canada, where it spreads across the continent from coast to coast. Aspens are well known for their clonal reproduction, which leads to large groves, or genets, of genetically identical trees, called ramets. Some investigators have claimed that aspens are the most massive organisms on the planet-clones in the western US can occupy as much as 200 acres. One well-studied clone in Utah, named Pando, covers 106 acres, has about 47,000 ramets, an estimated weight of 6,600 tons (greater than the weight of the largest sequoia), and an estimated age of 80,000 years.

However, aspens can also reproduce by seed, and frequently do. In the eastern part of its range, aspen clones tend to be quite small. Reasons for this could be that conditions for seedling establishment may be better there than in the west, or that conditions for clonal expansion are worse, perhaps because of competition from other tree species. Even in the west, the size of clones is highly variable across the landscape, determined by such factors as rate of root extension, rate of ramet production, extent of sexual reproduction, frequency of disturbance, and genet age.

Environmental conditions ultimately control genet size, by affecting the factors listed above. Those conditions that favor the growth of aspen may favor one reproductive strategy over the other, thus affecting the number and size of groves (discrete patches of aspens), as well as the size of genets. Conditions that are not favorable for aspen growth may cause reduction in the amount of land area covered by aspen, and lead to a distribution of groves that is not representative of clone distribution. In an area of relatively small groves, the association of groves and clones may provide information with which to make inferences about past and present environmental conditions.

This study was done in the Laramie Range of southeast Wyoming, near the regional boundary of aspen's range. Here, aspen is restricted to drainages and seepages where soils are moist, and forms groves that may be quite extensive in one direction (along the drainage), but are always narrow. Other, disjunct, groves are small. Our goal is to determine if the groves that are present on the landscape represent clones. Armed with this information, we will speculate on the reproductive mode of aspen in this area, past environmental conditions, and whether aspen is currently expanding or contracting.

Methods

We selected two groves at or very near Blair Picnic area (arial view shown right) in the Pole Mountain unit of Medicine Bow National Forest, approximately 21 km southeast of Laramie, WY, and 48 km west of Cheyenne, WY, elevation 2458 m. The larger of the two groves, named Bertha (B; 41°11'19.8"N 105°23'35.88"W) is located directly south of, and adjacent to, the picnic ground. The smaller grove (Grandmother's grove, G; 41°11'16.58"N 105°23'33.23"W) is southeast of Bertha, separated by approximately 13 m of open space. Both groves are located on the east side of the creek valley, and are bounded to the west by wet meadow and to the east by sagebrush and grass covered hills.

For each grove, the number of ramets was either counted (G) (shown below) or estimated (B), the size of the grove was determined, and three cores were taken. For coring, trees were selected to represent an age distribution, based on size, from old to young, though saplings were not included.

Leaf samples were collected by each student to represent the two groves and an "outlier." Each sample consisted of two healthy-looking, green leaves. One leaf was used for DNA extraction and the other stored at -20C for posterity. Four samples were made from Bertha, the larger grove, and three from Grandmother's Grove. The outlier sample was collected approximately 100 m NW of the nearest edge of Bertha (at 41°11'22.8"N 105°23'39.2"W), and separated from Bertha by a road and a meadow. However, aspen trees are present in a strip that is nearly continuous from Bertha to the outlier's location.

Results

The students extracted DNA from their samples (show in image below) using Berry Center facilities and  analyzed the data for genetic fingerprints.

Lab write up by K. Brenner (student)

Lab write up by K. Wilson (student)

Lab write up by M. Curry (student)

Lab write up by E. Robinette (student)

Aspen research poster by D. Tuthill and K. Parfitt (instructors)

Above: Kim Parfitt (Central High School, Cheyenne) and her AP Biology class extract DNA from their aspen leaf samples at the NAEF in the Berry Center.  Here they hold test tubes containing the DNA strands, later analyzed for DNA fingerprints.

REFERENCES

Grant, M. and J. Mitton. 2010. Case study: the glorious, golden, and gigantic quaking aspen. Nature Education Knowledge 1: 40 http://www.nature.com/scitable/knowledge/library/case-study-the-glorious-golden-and-gigantic-13261308

Kemperman, J.A. and B.V. Barnes. 1976. Clone size in American aspens. Canadian Journal of Botany 54: 2603-2607.

Mock, K.E., C.A. Rowe, M.B. Hooten, J. DeWoody and V.D. Hipkins. 2008. Clonal dynamics in western North American aspen (Populus tremuloides). Molecular Ecology 17: 4827-4844.

St. Clair, S.B., J. Guyon and J. Donaldson. 2010. Quaking aspen's current and future status in western North America: The role of succession, climate, biotic agents and its clonal nature. Progress in Botany 71: 371-400.