Earning stage names like Skeletorus and Sparklemuffin, male peacock spiders perform a colorful song and dance nearly unrivaled in the animal kingdom. But a new study shows that their main audience—the females they aim to woo—don’t impress so easily.
The new findings, published Tuesday in the Proceedings of the Royal Society B, emphasize the remarkable extent to which males across the animal kingdom compete for the affection of a single female.
Peacock spiders’ recently discovered courtship displays are among the gaudiest and most complex ever discovered, a fact made all the more surprising by their size. The little audiovisual spectacle measures less than a quarter-inch (five millimeters) long.
“The combination of complex mammal-like behaviours, their small size, [and] their color patterns [are] simply irresistible,” says Jürgen Otto, a mite biologist with Australia’s Department of Agriculture and Water Resources whose groundbreaking hobby videos first gave peacock spiders a wide human audience. “It is difficult not to get obsessed with them.”
When a male peacock spider thinks he has spotted a female, “the world pretty much disappears,” says Michael Kasumovic of Australia’s University of New South Wales, one of the study’s co-authors. The spider then begins a series of dances—including moves scientists have dubbed the “rumble-rump” and “grind-rev”—that send literal good vibrations through the ground toward the female.
Once he has piqued her interest, the male unfolds a brilliantly colored abdominal flap and then struts back and forth, all the while frantically waving specially colored, lengthy legs.
What a Girl Wants
But it takes two to tango, and researchers didn’t know exactly how females were participating in and responding to the ritual. What were the ladies looking for in a strutting, shivering suitor? And were the males’ bright colors actually related to finding a mate?
To find out, Ph.D. student Madeline Girard of the University of California, Berkeley, traveled to Sydney, Australia, and collected 64 pairs of the peacock spider Maratus volans, each duo consisting of a male and virgin female. Each pair went into what Kasumovic calls a “courtship arena,” an enclosure surrounded by cameras with a floor made of stretched pantyhose.
The homespun setup allowed Girard to detect the vibrational dances and leg-waving movements of M. volans males, while tracking how the females responded.
The team found that females don’t automatically swoon to the males’ advances, instead turning toward or away from them during their initial vibrations, based on interest. Some females also had more aggressive responses, rebuffing males with quick shakes of their abdomens—or worse. “If females don’t like a male, they’ll eat them,” says Kasumovic.
The females liked only 16 of the 64 courtship dances. In these uncommon instances, Girard found that males’ looks were about twice as important as their dance moves, though each plays a slightly different role in piquing and retaining a female’s interest.
Perhaps it’s not surprising that the spiders rely on visuals. Peacock spiders have an excellent sense of vision, honed by a need to stalk and then pounce on prey without the aid of a web.
Researchers praise the study for explicitly proving that “all these male shenanigans have evolved through females preferentially mating with males that display colorful, complex courtship displays,” says Marie Herberstein of Australia’s Macquarie University, who wasn’t involved with the study. “This link is rarely directly established.”
But questions remain. It’s unclear what females are homing in on within the males’ colorful patterns. And how peacock spiders became so showy in the first place remains a mystery. “Did it all start off with the dance and the color followed?” asks Herberstein. ”Or did color, movement and vibration evolve simultaneously?”
What is clear, though, is that when it comes to sex, male peacock spiders have a life-or-death imperative to listen to their partners.
“There’s an amazing amount of control that females have over the entire thing,” says Kasumovic. “If a male doesn’t listen to her feedback, not only will he be unsuccessful—he’s likely going to die.”
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