ASU Research E-Magazine: Following the Fighting Females

Mt. Graham’s gauntlet of hazards is imposing, but it does not deter Sarah Woodley’s research interests in southeastern Arizona. Monsoon thunderstorms can roll over the mountain during a summer afternoon, pelting flora and fauna with furious wind, rain, and hail. Javelinas and black bears meander the ponderosa pine forests of the 10,717-foot mountain, foraging for food. Snakes prey upon mountain spiny lizards as they try to defend their territories from one another.

A hiker would make plenty of noise to frighten bears away. Backcountry visitors would give javelinas and rattlesnakes wide berths to avoid provoking them. And no one would risk attracting lightning by carrying a metal fishing pole along a mountain trail during monsoon season.

Woodley is a biology doctoral student at Arizona State University. Her scientific instincts overrule her instincts as a disciplined naturalist. That’s why she sits passively in the forest, occasionally startling wildlife that happen upon her. Risks accepted, Woodley enjoys the opportunity to study the aggression of female mountain spiny lizards.

Woodley prefers the daylight conditions needed to study mountain spiny lizards compared to her last scientific gig, which involved evening studies of salamanders for her master’s research. It was spooky to be alone in the dark forest at night, she says. Salamanders are nocturnal. Nighttime was study time.

For the past three years, Woodley has studied the behavior of five-inch long mountain spiny lizards. She collects blood samples and measures levels of aggressive behavior during annual cycles.

Mountain spinys are abundant along the wood-lined creeks of Arizona sky islands like Mt. Graham. They do not fear humans. The lizards are good candidates for behavioral and hormonal studies because they are easy to watch and easy to catch. Researchers need only avoid the many other hazards that come with the wilderness territory.

Arizona forms the northern part of the mountain spiny lizard’s range. Both males and females are intensely territorial. Their furious pushups physically broadcast to rivals, “Here I am. Don’t come into my territory.”

At least that is Woodley’s interpretation of nonverbal lizard lingo.

Woodley studies the influence of specific gonadal hormones on female aggression in mountain spinys. Females will defend their territories by displays of pushups or by extending their dewlaps (throat flaps). They also charge and bite intruders. The lizard’s defense of territory means an observer can find the same individual on the same rock day after day.

“Females are aggressive in many species, but relatively little is known about the physiological basis of female aggression,” Woodley says. “Both male and female lizards aggressively defend their territories. Testosterone facilitates aggression in males, but the hormonal basis of female aggression is unknown.”

Michael Moore is an ASU professor of biology and one of Woodley’s advisors. Moore studies male aggression in lizards. He says that mountain spiny females are more aggressive than females of other lizard species. Finding out why seemed like a worthy project for Woodley, who wanted to establish her independence as a researcher.

“This species is totally unafraid of humans,” Woodley says. “We can do our observations and they don’t get distracted or change their behavior. Female aggression may be important in determining mating and social systems.”

During her last round of field study, Woodley worked in a forested area about 2,000 meters up the side of Mt. Graham. The mountain is located in the Coronado National Forest about 60 miles northeast of Tucson. Mt. Graham is black bear country. From her silent observation post perched atop a rock, Woodley saw many bears. The hiker in Woodley knew that she was supposed to make noise when in bear country. Scientist Woodley had to remain silent.

Woodley was more wary of the javelinas—because of their sharp canine teeth—and the “jumpy” cattle that graze through the forest. Snakes often preyed upon her lizard subjects while she recorded behavioral data. Monsoon thunderstorms filled the sky late in the afternoons. Woodley got wet many times. Despite the attractions and distractions, she made her observations and collected 60 female spiny lizards over a seven-week period.

Back in the Moore’s ASU laboratory, Woodley anaesthetized and performed surgery on each of her captured reptiles. She removed the ovaries of some females and gave others a testosterone implant.

A second group of lizards served as controls. They underwent sham surgery in which nothing was removed or implanted. The lizard surgeries were not traumatic. Each required no more than 15 minutes. The survival rate was 100 percent.

Each patient went home the day after surgery. Each was marked with a harmless paint stripe for later identification. Woodley says the lizards acted skittish for several days. As a result, she waited three weeks before making new behavioral observations. During those three weeks, she visited the site every other day to help the lizards get used to her presence.

Woodley watched to see how the surgically-altered females reacted to intruders. She used a fishing pole and dental floss to manually place intruders on rocks in the territories of other females.

Females without ovaries showed a decrease in aggression. Since ovaries are the main source of the hormone estradiol, Woodley hypothesizes that estradiol plays some role in aggression.

Female lizards with testosterone implants rated high in displays but low in charging intruders. The testosterone wore off over time. Woodley thinks the hormone may have caused females to exhibit male-like courtship displays.

Sham surgery apparently did not alter the lizard’s behavior. More than 70 percent of those females charged and bit intruders.

Moore says that his student’s research is significant because most investigators have assumed that aggressive competition is a characteristic of males. They have ignored the large number of natural contexts in which females aggressively compete.

“Sarah’s study of how hormones affect aggression by females in a natural context is pioneering work in the area of hormonal control of female behavior,” he adds. “Her work also promises to tell us much about how hormones affect aggression in males and females in different ways.”—Dennis Durband