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The Mystery of the Lek : How Choosy Female Medflies Pick Their Tough and Tender Males

May 10, 1987|WILLIAM JORDAN | William Jordan is a writer who was trained as a biologist.

Anyone who knows anything about the way Medflies mate has got to get a kick out of the way we humans think about mating--or, closer to the truth, the way we over think about it. Take the matter of the tough and tender male, currently in vogue in these liberated times. Medfly males have been aggressive and gentle for several million years, at least. The females won't have it any other way. The facts about Medfly relationships have been collected by Ken Konishiro at the University of Hawaii, Hawaii being a paradise for Medflies. And the story goes like this:

On the island of Maui, in a farmer's backyard, in the foliage of a lemon tree, there lies a typically enchanted spot. The sun sprinkles down onto the leaves of this spot in a particular way, and every morning about 9 o'clock male Medflies start to arrive. Within five minutes, they have all gathered in an 8- to 10-inch sphere of space among the lemon leaves, four to eight vigorous young bucks drawn together for one reason: the passing of the genes. Medflies use a method called "lekking," in which males congregate on communal grounds in order to attract and court their females.

No one knows exactly why this area is so special to the flies, but Konishiro is pretty sure that the quality of light is a critical factor. Wherever Medflies form a lek--it could be a coffee bush, a mango tree, a peach--it is always in a similar setting. Beyond the lighting, it's difficult to tell. The lay of the land, the color and outline of the foliage, the kind of tree--probably all these play some role. But whatever it is, the years pass, the leaves fall and the next generation of males gathers on the next crop of leaves every morning at 9. Then the preliminaries begin.

At the center of the lek lies a single leaf that is, to a Medfly male, the only place to be seen. It is the prime real estate in the lek system. This sets up the classic situation of ecological competition--a resource in short supply, one leaf and five males--and like males everywhere, the Medflies fight for what they covet. The one who gets there first tries to defend the leaf against all comers. Like minuscule rams, they butt heads until one gets dislodged from the leaf, or, in what looks like a contest of pure will, two approach each other, touch antennae and then sit there for about five minutes until one simply gets up and leaves. How is this latter kind of victory won? It is a mystery of the lek.

When the fighting dies down, a territorial hierarchy has evolved in which the dominant male owns the choice property, with the lesser males owning adjacent leaves, all arranged like planets around the sun. The lek now goes into operation. The males take their positions, always on the underside of the leaf, and emit a scent--a pheromone--which rises into the air, commingling with the scent of the others and drifting downwind. "By banding together," Konishiro says, "they can produce a lot more pheromone, and they'll have more of a chance of reaching the females."

It's a curious fact that females seem to respond one at a time. She traces the pheromone back to the lek--and heads straight for the prime real estate, where the top male is awaiting her visit. She has no interest in the surrounding properties; the other males are losers as far as she's concerned.

The dominant male, being on the under surface, has no way of knowing the female has alighted unless the sunlight is falling on his leaf. If it is, the leaf glows like a solid green TV screen to anyone viewing from below. And on this luminous background appears a silhouette of the male's prospective mate, like an Indonesian puppet. He immediately aligns himself with the image above so both are facing in the same direction. Then he pulls his abdomen under his body and begins vibrating his wings. This pulls air from behind and blows it forward, undoubtedly freighted with a new, more seductive scent. It drifts up around the edge of the leaf and reaches the female. She walks toward the edge, guided by the scented breeze, climbs over to the underside, and walks to within about two millimeters of her suitor. There she stops, facing him head-on.

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