Research Stories

by Margaret Coulombe

Stan Faeth has spent the past 27 years as a professor of life sciences at Arizona State University. He was hired as a professor straight out of graduate school. But despite interests in geology and paleontology, a career as a professor was not in his plans while growing up in Kentucky. It all began a bit differently for Faeth.

Was he a budding Jacques Cousteau wannabe? No way. Faeth was always more of an outdoorsy Jack Kerouac, the confessional-style poet of the Beat Generation who traveled aimlessly across the United States. Faeth hitched his way across the U.S. and Canada after earning his undergraduate degree. He traveled where fate or the road led him.

Fortunately, the road led to professor Thomas Kane at the University of Cincinnati in Ohio. Kane became Faeth's master's degree mentor.

Kane was a well-loved and respected evolutionary ecologist who studied cave invertebrates. He passed away in 2007. Faeth was Kane's first graduate student, and he credits the UC professor with setting him on his path to ASU.

"I wasn't particularly focused," Faeth says. "I was interested in microbial ecology, but I was young, green, and naive. He helped rein me in and introduced me to insects. I would never have survived without Thomas Kane."

Kane directed Faith's budding environmental interests toward the pursuit of understanding a tier of intertwined ecological relationships. What exactly are the interactions between microbial symbionts, plants, herbivores, and predators? The work has led Faeth in directions ranging from birds to cancer cures.

Symbionts and ecosystems
Microbial symbionts include small fungi, bacteria, and viruses. Faeth says they are found in nearly all organisms. They exist in the guts of animals, the interiors of corals, and the roots of plants.

One example is the mycorrhizae that live in the belowground parts of corn and other. The symbionts enhance nutrient uptake. Another example is the bacteria that live in the guts of termites and cows. The bacteria actually break down cellulose from the wood or plant material eaten by the insects or animals. In these cases, both the host animal and the bacteria mutually benefit.

The results are not always beneficial. Faeth says that the effects of symbionts on the host can run the gamut from mutualistic to pathogenic. He points to the imported fungus responsible for chestnut blight.

"Chestnuts were once a dominant tree in the eastern deciduous forest," Faeth explains. "The trees were an important food source for insects, animals, and Native American populations." The fungus eliminated chestnut trees from North America.

Faeth is fascinated by the range of effects that fungal symbionts can potentially have on their hosts, and how those relationships evolved. He has a particular interest in the grasses native to Arizona.

Fungal symbionts are called endophytes. They are found in many different plants. Endophytes can live on bark, leaves, stems, and roots. They are primarily found in the aboveground parts of grasses.

Some symbiotic bacteria are well understood. They fix nitrogen in legumes and mycorrhizae in the roots of many plants that increase nutrient uptake. As a result, they provide a nice a source of fertilizer. But endophytes in grasses produce some unusual chemicals. The effects of these chemicals are less clearly understood. Scientists call these chemicals "secondary metabolites."

In many systems, Faeth says these metabolites have been found to be detrimental to plant-eating animals. The relationship between the endophyte and the plant grass is a benefit to both. Distasteful leaves mean fewer animals chomping away and better plant survival, right? However, as with all relationships, Faeth is proving that things are much more complicated than previously believed. The effects are far-reaching.

"Endophyte infections in grasses can cause shifts in the diversity, abundance, and species compositions of entire communities," Faeth says. They can affect the plant eaters, the predators, the parasites, and the scavengers.

Sleepy grass, LSD, and cancer cures
Ergot alkaloids provide a great example. The alkaloids are chemicals produced by fungus on plants. These chemicals are better known as lysergic acid diethylamide, or LSD for short.

The hippy-era fascination with LSD spawned a bevy of human social byproducts: acid rock, Haight Ashbury, and the Summer of Love in 1967.

Ergonovine is another potent alkaloid produced by the fungal endophyte Neotyphodium. Both have played a role the evolution of grasses, their herbivores, and their predator communities.

Faeth was one of the first researchers to ask these questions about native grasses. His group studies two grasses native to Arizona. Arizona fescue (Festuca arizonica) is one. The other is robust needle grass (Achnatherum robustum), also known as sleepy grass. The plant gets its name for its sometimes narcotizing effect on grazing cattle and horses. It is not hallucinogenic. In fact, in early South American cultures, mothers would calm their infants by giving them a single grass seed to eat.

So would Old Paint benefit from a trip to this field of greens? Faeth says that vertebrates avoid sleepy grass. But what about insects and other arthropods?

Faeth's experimental fescue plot has red cones placed to permit aeration of the soil in treatments designed to restrict water availability. Some plants are also caged to exclude herbivores.

Faeth has a study site at the Arboretum in Flagstaff. A trip there helps tell the tale. At first glance, the abundance of red inverted funnels and wire cages weighted with rocks looks artfully indecipherable. However, four different genotypes of plants are laid out in a carefully planned grid. In each year-long study, a total of 240 experimental and 30 control plants are examined. Tufts, with and without fungal endophytes, are tested to determine the effects of rainfall, irrigation, drought, and herbivores (or lack of herbivores). Faeth's findings have been surprising.

"These endophytes are usually considered evolutionary dead ends," Faeth explains. "They are asexual and they attract arthropod herbivores, rather than repel them. This effect can vary with environmental factors like fire, drought, nutrients, etc. This might regulate the endophyte-plant-herbivore-predator community structures from site to site."

Such findings go against those found in other systems and studies. But Faeth has a theory about that, too.

Lots of people prune their trees and cut their grass. The ASU scientist says that cutting creates more reproductive structures and grass seeds.

"In native grasses, we believe that endophytes may be encouraging herbivory, or the eating of the plants. This helps to produce more seeds and more opportunity for endophyte-infected seeds to be distributed—even at the long-term expense of the plant," Faeth says.

The enemy of my friend is my friend? It's an evolutionary twist that yields more seeds, more grass, more endophytes, more herbivores, more predators, and more overall abundance in a community—all manipulated by a microscopic organism.

Faeth's work on these tiny microbes, their chemicals and desert plant hosts has led to other discoveries: anti-cancer agents. Leslie Gunatilaka is a natural products chemist at the University of Arizona. She and Faeth have screened a range of native plants and shrubs for endophytes. They've also analyzed their associated metabolites.

The scientists found potent anti-cancer agents in two plants. Extracts from the stick-like Mormon Tea and the cholla Christmas cactus yielded beauvericin, bikaverin, and other anti-cancer compounds.

Faeth is quick to point out that this is not an entirely unknown phenomenon. The yew tree contains the anti-cancer agent taxol. Scientists now think that the chemical comes from endophytes in the bark of the yew, rather than from the plant itself.

The findings by Gunatilaka and Faeth mean that Arizona native plants and their microbial partners may represent an untapped treasure trove of compounds. These chemicals may have the potential to impact human health and control disease. But first, the plants must be conserved.

Urban ecology and conservation
Urban areas in the Southwest are expanding rapidly. Growth in the Phoenix metropolitan area is faster than most regions in the world. Urban sprawl puts tremendous pressure on surrounding desert landscapes and animals. Still, little is understood about urbanization's potential long-term effects on the environment and how best to assess its conservation. Faeth's work is about understanding basic patterns of biodiversity and food webs in urban habitats.

The ASU scientist's research and that of his colleagues are busting myths. The findings offer novel ways to assess and understand our urban environments and their impact on Arizona's wild areas.

Faeth says that things are often not what they seem in urban areas. For example, some landscapes look like deserts or desert remnants. These are areas that we preserve. Other yards are built to look like deserts. But these areas don't really function like desert land anymore.

"Human activities have caused this uncoupling. We are changing nutrient availability," he explains. "There are nitrogen pollutants from agriculture and in aerosols from cars and even fast food. And urban xeriscapes tend to have higher productivity because people water their yards nearly as often as they might grass. Consequently, there are more herbivores, more types of insects, and a greater abundance of birds that prey on them.

"Things are also shifted seasonally in the cities," he continues. "Instead of going through the boom and bust that you normally find in the desert, things are in bloom all year round."

The array of interactions and impacts can be very confusing. So what is the best way to approach issues of biodiversity, conservation, and preservation in our deserts and urban areas?

Faeth hopes that insights from his group's studies will provide solutions. They've already contributed plenty over the years. Getting more useful answers may only be a matter of Faeth.

Stan Faeth's research is supported by the National Institutes of Health, National Science Foundation, and the Arizona Disease Control Research Commission. To hear Faeth speak more about his work, go to the Ask-a-Biologist Web site: http://askabiologist.asu.edu/podcasts/index.html#Faeth