Fowl Play : Biology Professor Studies How Females Select Mates

There are those who pity the world’s scientists, believing them to be anchored to their microscopes and missing all life’s fun. These people have not met Marlene Zuk.

Zuk is an evolutionary biologist. But what she really does is watch wild fowl mate.

“It sounds pretty crazy, doesn’t it?” said Zuk, 35, a professor at the tree-studded University of California campus in Riverside. “Here I am with my Ph.D. and I’m watching chickens have sex.”

There is, of course, a noble purpose to this voyeurism. Zuk is studying how wild hens select their mates, and investigating the influence of those choices on the very evolution of the species.

Oddly, it is not hefty size, flashy feathers or a thunderous crow that make a rooster irresistible. In four years of experiments involving more than 800 birds, Zuk and two colleagues found that hens pick suitors with bright eyes and large, dark red combs and wattles--all indicators of vigor and health.

The hens, it seems, aren’t looking for hunks. Instead, Zuk said, they want what all sensible mothers want--good, disease-resistant genes to pass on to their young.

“The characteristics important to the female are those that reflect the male’s resistance to pathogens and his overall condition,” Zuk said one recent morning as she looked in on several clucking members of her flock. “These traits are like an advertisement for the males, a promise to the hen that her offspring will somehow be more fit and more able to withstand the environment.”

Zuk’s research is among a bundle of ongoing studies in the United States and abroad that address an issue long ignored by science: how female mate selection has influenced the appearance and behavior of males.

Charles Darwin, in the 1870s, was the first to give females credit for influencing the evolution of their species through their choice of reproductive partners. But his theory drew scoffs of disbelief from other scientists, and popular opinion for decades held that females were arbitrary in picking their mates.

Now, more than a century later, the female is finally winning some respect in these matters. Research by Zuk and biologists studying frogs, beetles and other creatures suggests that females in fact wield a powerful evolutionary weapon when they select a male.

“This is very exciting work, because it gets right down to one of the basic questions of biology: what makes males male and females female, and how did that evolve,” said Zuk, whose conclusions have been published in the journals Evolution, Behavior, American Zoologist and the American Naturalist. “Understanding this is really critical to understanding life.”

Zuk, a professor at UC Riverside since 1989, has won nationwide prominence with her research, scientists familiar with the work said. While her hypothesis is by no means universally embraced, it has recently been “one of the major focuses for research interest in this whole field,” said Mark Kirkpatrick, a zoologist at the University of Texas in Austin who studies female mating preferences and male traits.

Thomas Eisner, a Cornell University biologist investigating the courtship rituals of a beetle species, agreed: “She’s sticking her neck out a bit, and a big idea like this needs more data before it wins everyone over. But I like the basic idea a lot, and there are many other adherents as well.”

Petite and bespectacled, Zuk (rhymes with cook) is indefatigably passionate about her work. Her hands dance through the air as she describes the intricacies of her unusual experiments. Detailing the biological mysteries still awaiting her inquiry, she leans forward across her cluttered, gray desk, appearing as eager as a child anticipating her first encounter with a polliwog.

But Zuk, who believes one should not take one’s work too seriously, has not overlooked the comical side of her fowl research. She keeps a rubber rooster mask and numerous chicken-oriented Far Side cartoons in her office, and cheerfully shares humorous scenes from the laboratory.

“We did one study to see if we could artificially manipulate the males’ ornaments and influence what the females did,” Zuk recalled with a grin, explaining how the scientists fashioned large, fake rooster combs out of latex and attached them to their subjects’ heads.

“People accused us of making sex aids for roosters,” Zuk said, and “joked that we’d get letters from desperate males--’Dear Dr. Zuk: I’m having no luck with the ladies. Please send an extra large comb.’ ”

Reared in Los Angeles, Zuk steered herself into biology because of a lifelong curiosity about animals and the way they live.

“I’m not into the cell stuff, really,” said Zuk, who teaches a vertebrate biology course on local species. “I like the behavioral side of it.”

Like sex. Zuk’s work on that topic began at the University of Michigan, where she completed her doctoral thesis on mate choice and male ornamentation in field crickets. She enjoys insects--replicas can often be found scattered on her desk and even pinned to her lapel--but in 1986 she switched to birds, wild red jungle fowl, to be exact.

Ancestors of today’s barnyard chickens, jungle fowl are native to Southeast Asia. The roosters have brightly colored feathers on the head, neck and back, red or orange eyes and fleshy red combs and wattles. The hens are much less spectacular looking, with their dark, speckled coloring designed for concealment in Asia’s thick jungle underbrush.

Zuk’s fowl experiments were conducted with two other biologists--Randy Thornhill and J. David Ligon--at the University of New Mexico, where she completed her postdoctoral studies. The scientists launched their work with birds from a large population of jungle fowl that roam free on the grounds of the San Diego Zoo.

The species was ideal for the research because its members have continued to reproduce and evolve naturally--unlike a laboratory rat raised under artificial conditions, for example--and the males have elaborate ornaments. They are also cooperative animals, Zuk said, easily tamed and bred.

One of Zuk’s experiments sought to distinguish precisely which male characteristic was a turn-on for the hens. Two roosters were tethered inside an outdoor enclosure, and the female bird was placed in a pen, from which she could see both of her potential mates. The roosters were prevented from seeing each other in order to eliminate the effect of male competition on the hen’s choice of a partner.

After an hour of what Zuk calls “window shopping,” the female was released and an observer seated behind a wall of one-way glass watched the courtship and mating ritual. A computer analysis of the data led Zuk to this conclusion: The roosters with the winning sex appeal were those with features suggesting resistance to parasites.

“It’s very crucial for females to make the correct choice in mate selection,” Zuk said. “Females produce relatively few eggs and therefore pay close attention to traits that guarantee them some measure of reproductive success.”

Over time, Zuk argues, females who made the correct choices passed their genes--and therefore their mate preferences--to future generations of hens, a process that ultimately influenced the evolution of the roosters’ traits.

Zuk believes that the female’s role in shaping evolution through mate selection is attracting attention largely because of the influx of women into science.

“There have been sociological biases attached to all sorts of scientific work, but that’s changing as the field opens up,” Zuk said. “With more and more women coming into science, we’re starting to look at this stuff and say, ‘Hey, shouldn’t we look at what the females are doing?’ ”