Tuesday, November 27, 2007

Fountain grass: Darwin-defying super-weed?

Fountain grass is among the really problem weeds of Hawai'i, but globally, it may be more than a problem weed.

It may, in fact, be a global superweed, violating understood standards of plant behavior.

(Photo: Big Island fountain grass. U.S. Fish and Wildlife Service photo by Marie Bruegmann.)

A team of scientists from the University of Hawai'i suggest the grass constitutes a “super-genotype.” They are Johannes Le Roux, Ania Wieczorek and Carol Tran of the university's Department of Tropical Plant and Soil Sciences, and Mark Wright of the Department of Plant and Environmental Sciences.

Their paper, “Super-Genotype: Global Monoclonality Defies the Odds of Nature,” was published this summer on the Public Library of Science's peer-reviewed online journal PLoS ONE.

Fountain grass is a problem in Hawai'i not only because it expands quickly and competes aggressively. It's also a fire fuel and is fire tolerant. That means it helps a fire sweep across the landscape by being readily ignited, and it recovers quickly from fire—often much faster than native plants.

It can be attractive in a garden setting, and has accomplished some of its expansion through escaping from cultivation. It is native to northern Africa. The paper's authors say it is now found, in addition to Hawai'i and the Mainland United States, in Australia, Democratic Republic of Congo, Fiji, Namibia, South Africa, Swaziland, Zambia and Zimbabwe.

But it is not equally invasive in each environment. As an example, they say, while it readily invades native forest areas in Hawai'i, it primarily goes into disturbed areas in South Africa and appears to be mainly along roadsides in Namibia.

The authors conducted genetic studies on the grasses, and found that there is amazingly little variability among them. Samples from “South Africa, Namibia, Egypt, Hawaii, Arizona and California share a single genotype.”

And yet, the grasses are growing in remarkably different environments. Highlands and lowlands, wet and dry, and some areas with significant limits on the amount of nitrogen available.

Most plants don't do well when you move them from one environment to a dramatically different one, although if they survive, their offspring after a few generations may evolve the capability to do well in the new situation.

The suggestion of the authors is that the fountain grass has a dramatic inherent ability to respond immediately to new environments, rather than needing to evolve to adapt to new circumstances.

Why would this be the case? They suggest that at some point in its past, in their native terrain, these fountain grass types “were exposed to constant environmental conditions that were extremely hostile” and rapidly fluctuating between dry and wet.

The researchers call this kind of flexible adaptiveness “plasticity,” and they suggest that fountain grass gave up for its plasticity some of its ability to evolve genetically. That's why, in widely separated parts of the world, fountain grass looks essentially the same genetically.

This is a pretty new idea in conservation biology. The standard story of the progression of life in places like Hawai'i and the Galapagos has been that of species—whether birds, plants or insects—that settle into new environmental niches, and then evolve to best take advantage of those niches.

Fountain grass represents another view: that some species carry a bag of tricks that lets them survive anywhere.

“In contrast to typical Darwinian evolution, the single super-genotype identified here persists and survives exposure under most environmental conditions. Further examination of other species may reveal further super-genotypes, and it may be found that this is a more common, significant but hitherto overlooked mechanism driving survival and local fitness of plant populations.”

© 2007 Jan W. TenBruggencate

See the article: www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0000590

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