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Even Educated Fleas Do It

CBS professor Marlene Zuk writes popular literature about mate selection, courtship and sex in the insect world, which sheds light on human behavior.

When you build a career on the animal kingdom’s vast diversity of sexual behavior, certain questions come with the territory.

Marlene Zuk gets "Is adultery normal?" a lot. Her standard reply: “What do you mean by that?” and “What is ‘normal’?”

A new professor in the Department of Ecology, Evolution and Behavior (EEB), Zuk will tell you that “normal” sexual behavior takes virtually every form imaginable. Her scientific writings include the essay “Family Values in Black and White” (about penguins, which sometimes form same-sex couples), and three popular books; the latest is Sex on Six Legs: Lessons on Life, Love, and Language from the Insect World.

“Insects have some of the most interesting behavior in animals,” she says. “A lot of people don’t appreciate how variable sex is.”

Zuk comes to the College of Biological Sciences after 20 years as a biology professor at the University of California-Riverside, where she also had oversight of faculty equity and diversity. She currently studies a species of Pacific field cricket in Hawaii, where a parasitic fly kills males after homing in on their mating chirps.

For many of those males, chirping brings doom, not dates. But all is not lost. Over just five years, a rare mutation that alters the wing structure and silences male chirping spread to more than 90 percent of the population, Zuk says. This cloaks the males from the fly, but also from potential lady friends.

Singing wing man

Or does it? The mutation couldn’t spread unless silent males were reproducing, so perhaps, Zuk says, notions about the crickets’ sexual repertoire were off base. For one thing, silent males seem drawn to chirping males, which should put them in position to meet females after all.

“Or maybe the less choosy females were selected for,” says Zuk. “I think crickets were much more flexible than we gave them credit for. A male may have a rule of thumb to move toward song if his own world is silent. And a female may be inclined to mate with a silent male if the whole world is silent. To test these ideas, Zuk and her colleagues will raise crickets in a state-of-the-art soundproof chamber in the Ecology Building. With acoustic conditions strictly controlled, they can observe the effects of sound on cricket behavior and reproductive success.

By combining studies of behavior and evolution, Zuk is a natural for EEB, says department head Scott Lanyon.

“We like to look for people doing good solid research at the interface of the subdivisions of biology,” he explains. “Marlene can easily identify herself as a behaviorist and an evolutionary biologist. That’s critical for having a truly integrated department and for training graduate students. We think that to be great in any of these three subdisciplines, you have to understand the other ones.”

Opening eyes

Notions and biases about the sexes have long hampered scientific work, Zuk says.

“For example, scientists have argued for a long time about the evolution of characteristics like the peacock’s tail or a cricket’s chirp, which may hinder a male’s survival but that are preferred by females,” she notes.

While Charles Darwin favored this idea, naturalist Alfred Russel Wallace, a rival of Darwin, didn’t buy it.

“Wallace thought the idea that females chose particular males was rubbish,” Zuk explains. “He thought some males just had excess energy and vitality.”

Also, the Victorians thought if peahens liked peacocks with big tails, it implied that peahens had an aesthetic sense—something considered exclusive to people in the upper echelons of society.

Today, most naturalists accept that Darwin was right about the basics: Female choice can help fitter males leave more offspring, says Zuk, who also supports the concept. Its central tenet is that males with showy but “useless” accessories are advertising that they are fit enough to invest energy on ornaments.

After decades on the academic scene, she suggests that women continue to lag behind men in the sciences largely due to bias in the way the sexes are evaluated.

“Even when we believe ourselves to be egalitarian, we may act to favor our unconscious beliefs about the sexes,” Zuk says. “The challenge now is to recognize those biases and correct them.”

To get students to think about how the sexes differ in their reproductive strategy (with behavior to match), Zuk asks them how many children a woman could have. Then a man. The answers are, of course, quite different, and so are the sexes’ reproductive strategies.

“This disparity between what will maximize reproductive success is at the core of sexual behavior and how it evolved,” Zuk explains. “Males and females are different—why is that? That’s at the basis of a lot of what I study. How can you not want to know why the sexes are different?”          

– Deane Morrison