Cattails and contamination: marshy stalks hold DNA clues on pollution

October 24, 1999

A team of researchers at the University of Cincinnati has detected significant differences in the genetic diversity of common cattails in areas heavily impacted by pollution, providing evidence that cattails might be an effective indicator of environmental stress.

Cattails were selected for study because they have a wide geographic distribution, from the Arctic circle to the tropics, and thus, could be used widely for stress monitoring. The research team, led by University of Cincinnati biologist Steven Rogstad, and involving UC mathematician Stephan Pelikan, Oak Ridge postdoctoral researcher Brian Keane, and U.S. Environmental Protection Agency scientists M. Kate Smith and Greg Toth, sampled dozens of cattail populations along a 320-kilometer stretch from Louisville, Kentucky, to Circleville, Ohio (south of Columbus).

In addition, five sites were sampled on the Wurtsmith Air Force Base in northeastern Michigan, because some of the sites were known to be contaminated with fuels, solvents, and other organic chemicals, while adjacent sites were unpolluted.

Leaf samples from the various sites were returned to UC labs and extracted for the DNA comparisons. The biologists focused on variable-number-tandem-repeat (VNTR) sequences, a type of DNA fingerprinting modified after similar techniques used with humans. By sampling a wide area in the Midwest and a site known to be polluted, the researches hoped to get a better picture of VNTR genetic diversity in cattails and to determine if changes in genetic diversity could be an indicator of environmental stress.

The team found two surprises. First, previous studies indicated that, although cattails are extremely variable in morphology and ecological tolerance, protein (allozyme) analyses had shown an almost complete lack of genetic variation across North America. With the more powerful VNTR analyses, the researchers found more variation in 30-foot by 30-foot plots than previously identified across the entire continent. Although this variation was high enough to permit the identification of different intermingling clones within plots, the amount of variation was the lowest yet found for natural plant stands using DNA fingerprinting.

Second, Rogstad notes that "several previous studies with animals found that genetic diversity is often reduced with increasing levels of chemical pollution." The researchers were surprised to find that the cattails growing in the most polluted sites had the greatest genetic diversity in their VNTR sequences.

Possible explanations for this increased diversity include increased mutation rates or higher mortality driving the establishment of a more diverse set of individuals at a site.

Rogstad's lab is continuing its work in this area and examining diversity in a number of common plants from dandelions to honeysuckles and wild raspberries. The work is supported by the EPA.

University of Cincinnati

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