How Toxic Grass Puts Animals to Sleep

Microbes called fungal endophytes turn needle grass toxic. The plant is known as "sleepy grass" for its sedating effects on animals. Researchers are studying these endophytes because of their impact on livestock grazing and native grasslands restoration. Here, Graduate student Andrea Jani collects arthropods from sleepygrass (Achnatherum robustum) in the Lincoln National Forest, New Mexico, with the Burkhard Vortis suction sampler. (Image credit: Stan Faeth, Department of Biology, University of North Carolina Greensboro)

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

Legend  has it that five railroad surveyors killed by Indians in 1854 in New Mexico lost their lives because they unwittingly allowed their horses to graze on "sleepy grass" the night before.  The next morning, under attack, they jumped on their horses to escape — but the animals were frozen in place. Without the means for a quick getaway, they were doomed.

Whether true or apocryphal — the story is unverified — it could have happened, considering the toxic effects of  sleepy grass, also known as robust needle grass, which commonly grows in many western states and causes animals who eat it to turn into living statues — or, if they consume too much of it, even die. 

"Native Americans are said to have fed a single seed to colicky babies to quiet them, and they — and ranchers — have fed small amounts to cattle to make them more sedate and easily managed when moving them from summer to winter ranges in the mountains," said Stan Faeth, professor of biology and head of the biology department at the University of North Carolina, Greensboro. 

Moreover, in a book called "Horse Tradin," by Ben K.  Green, the author recounts "how he bought a horse from the Mescalero Apaches in the 1920's which seemed tame and broken, but later found it was unbroken and wild — but had been fed a small amount of sleepy grass," Faeth added.  

Sleepy grass has this effect because, like all plant species, it harbors microbial "partners," that is, microbes such as bacteria or fungi that "infect" the plant and live within plant tissues. They can dramatically change plant growth and performance, frequently to the plant's benefit. Also, like plant and animal species, microbes also can hybridize and create new genetic species and variants. 

Fungal endophytes, which are found in many types of grasses, make alkaloids which fight against drought and insects. But, as is the case with sleepy grass, these alkaloids also can be poisonous to animals — including humans. 

"If ingested, infected sleepy grass — but only from a few selected populations — has the same effects on humans as in livestock," Faeth said. "One main alkaloid is lysergic acid amide — very closely related to LSD, but apparently without the hallucinogenic effects."

Faeth and his colleagues, which include Nadja Cech, associate professor in the university's department of chemistry and biochemistry, are trying to better understand the workings of fungal endophytes. Because their research could have broad implications for the multi-billion dollar livestock industry, as well as for the restoration of native grasslands and the management of forage grasses, the National Science Foundation is funding the program as part of the American Recovery and Reinvestment Act of 2009.

In replenishing native grasses, for example, it would help to know whether seeds were infected before planting them. The knowledge also could help the turf grass industry in the planning and maintenance of recreation areas. 

"You can plant grass with high endophytes in places where nothing is grazing — golf courses, for example," Faeth said. "The grass uses less water and resists insects. It's good for golf courses, but you don't want to plant it in pastures where it will make livestock sick."

Faeth's team has been conducting field experiments in Arizona on two native grasses — "sleepy grass," and Arizona fescue. The endophytes within Arizona fescue also make alkaloids but they are harmless to livestock.

The research team has created "common garden experiments" to understand how the endophytes work within the plant, and whether changing certain conditions can increase the grass's ability to survive and compete better in harsh environmental conditions.

"We take plants with different strains of endophytes and grow them," he said. "Then we alter the factors that can change the endophyte effect on the host — such as water, nutrients and competition. The alkaloid production stays the same. We are looking at the plant's response in terms of growth and reproduction — how does the plant respond to these variants? We want to better understand how [endophytes] work." Endophytes sometimes are not beneficial to the plants, depending on the strain. "We are studying this as well," Faeth said. Although generally thought to be positive to plants, "most of our research is showing you can get highly variable effects," he said. Also, one section of land can have mixed strains containing areas with toxic-producing endophytes — or not. There's no way to tell without testing — although livestock, once sickened, will not eat there again.

Faeth and his colleagues also have been collecting native grasses in very remote mountainous areas of New Mexico — Lincoln National Forest, near Cloudcroft, for example — as well as insects from the plants. They want to test the effects of endophytes and their alkaloids on herbivores. "Just like livestock, endophytes may protect grasses from insect consumers," he said. 

They gather the bugs using a machine that suctions them out of the plant, called a Burkhard Vortis Insect Sampling device. "It makes a lot of noise — it runs on a gas leaf blower engine —and looks like some type of weapon," he said. 

These field trips may seem relatively benign, but sometimes the unexpected happens. "On more than one occasion, we've had the local ranchers approach us, gun-in-hand, wondering 'what the hell are you doing out here?'" he said. 

Another time, a rancher and his wife — who happily gave permission for the researchers to work on his land — often enjoyed chatting with the three young undergraduate and graduate students Faeth brought along — all of them women, and all raised in the city. 

"The rancher would take us in his pickup truck to a remote location on his property, where there was a stand of sleepy grass," Faeth recalled. "On one trip, without saying a word, he stopped abruptly, jumped out, retrieved a shotgun from the bed of the pickup truck, and blasted off two deafening rounds, startling my students."

To their horror, the rancher walked about ten meters, picked up a dead wild turkey, returned to the truck, threw it in the bed, and got in. Then, to the amazement of the wide-eyed students, he uttered but a single word before driving off: "Dinner."

Editor's Note: This research was supported by the National Science Foundation (NSF), the federal agency charged with funding basic research and education across all fields of science and engineering. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. See the Behind the Scenes Archive.

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