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Background Noyce: Professor Susan Villarreal

Professor Susan Villarreal is an entomologist specializing in mating rituals.

By Andrea Baumgartel

“I focus on aspects of behavior that impact an organism’s life, and try to understand why they’re behaving the way they are,” said Professor Susan Villearreal.

She is an entomologist who has started teaching Bio 150, 240, and 252 this year and is developing a brand-new Forensic Entomology course. Among other exciting projects, she is working to complete and curate the insect collection at Conard Environmental Research Area (CERA), Grinnell’s 365-acre field station of restored prairie.

“At the end of the summer, I want to have a complete, curated insect collection and examine how, for example, in one part of CERA there’s an old growth field—let’s look at the insects out there and see what species are inhabiting that area, and see how its composition differs from, say, the forest or managed plot areas,” Villarreal explained. “I hope to have [the collection] to be very applicable for all sorts of uses that people will have in the future.”

Villarreal has studied a wide range of topics, from looking at molecular tools to manipulate mosquito-mating behavior (ideal for disease control), to characterizing the complex mating duets of Scudderia pistillata, a katydid local to parts of the Midwest and Eastern U.S.

“Insects have so much diverse, weird and fun behavior—and they manage it all with very rudimentary stuff. Basic neuronal stuff, but they’re able to do wildly complex things. The more you probe into it, the more you find,” Villarreal said.

Currently, Villarreal focuses on the pre-mating behavior duets, or acoustics, of Scudderia pistillata. Along with other acoustic insects, Scudderia pistillata have their own, distinguishable, species-specific sounds. The male calls at night in the summer and the female gives a response.

Professor Susan Villarreal is an entomologist specializing in mating rituals.

But things get complicated—fast.

First, these calls have specified, quantifiable time sequence. The female doesn’t call back immediately, but waits for a brief time before making her own call—a slightly delayed response.

Second, each Scudderia pistillata male has his own idiosyncratic call. And with so many males calling at once (the chorus), this leads to competition amongst the males all vying to be chosen by the female. This choice—the pre-mating decision of the female—is Villarreal’s main research goal for this upcoming summer.

“[I use] microphones to play different calls to the female and listen to her response, as well as the way that she changes in terms of what she’s paying attention to. This one male might have this type of call and this other male has a slightly different call—does she have a preference for one above the other? Who she chooses in the environment tells us key things about the interactions of the chorus,” Villarreal said.

Villarreal also studies the huge physical and acoustic interactions within the katydid chorus. Because the katydids need to make themselves both audible and distinguishable, “You get so many elaborate singers and variation.”

Sometimes, when males get too close, they’ll fight—wing-flipping and leg kicking galore. But since having a chorus of males is more audible, and therefore advantageous, it rarely gets more violent than that (for katydids, at least).

What makes a female katydid choose one particular male over the other? Again, the answer lies in the calls.

Every time a katydid sings, it rubs its wings together—think Zzt-zzt-zzt! But the length of these Zzt’s! can increase or decrease. Villarreal has found that the females seem to prefer males who have the longest calls, and believes that female preference is one of the ways in which species-specific calls develop. In the katydid’s case, female preference has put selective pressure on these calls to become longer in duration. Although, when Villarreal tried playing unaturally long calls, the females didn’t show a preference—sticking with species-specificity.

All of these sounds are going to be making their “voices” heard very soon.

“It’s something all around us, but we often overlook it,” Villarreal said. “Start looking out for all of the spring sounds. The spring peepers [frogs] are starting now—they’re the first vocalizers besides birds. Then the spring crickets pop up, and then as it gets warmer, the cicadas, katydids, tree crickets.”

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    Bug boyApr 21, 2017 at 2:21 am

    The females of most crickets and katydids walk silently toward the male that they have chosen and avoid predators. But it seems like your females advertise their whereabouts when they respond to the male’s call. Is there some advantage to that behavior?