Squid gather by the thousands to spawn in what look like chaotic orgies. But that appearance is deceptive. A team of biologists recently had a rare opportunity to study spawning squid off the coast of South Africa. They found that the tentacled couplings are anything but random. The mating behavior of squid, it turns out, is surprisingly complex and competitive.
Roger Hanlon of the Marine Biological Laboratory at Woods Hole, Massachusetts, and other divers videotaped the spawning underwater. They also implanted radio tracking devices on some of the squid that allowed them to track the animals’ movements day and night. The researchers found that the squids’ behavior varied with their distance from shore. Offshore, away from the crowded orgy, isolated pairs apparently mate in a head-to-head position, and the male places a packet of sperm in a receptacle below the female’s mouth, where she can carry it for months. “So if they meet that one special guy early on, they can hang on to his sperm,” says Hanlon.
Inshore, close to where the females deposit their eggs, the crowds grow, and large males fight for mates. The victors approach females differently when inshore. Grasping the female from underneath, they place their sperm in her mantle cavity, near her egg chamber.
After mating, the female withdraws a string of 200 jellylike eggs from her mantle, giving the sperm of the large males the first shot at fertilizing them. Then she holds the string in front of her and has the chance to release the stored sperm of her earlier mate from the receptacle below her mouth. But as she holds the eggs in her arms, smaller males make their move. “They can’t beat big males in a fight, so they sneak,” Hanlon says. “When they see the female with the eggs in her arms, they make this rapid dart — they leap onto her arms and deposit sperm directly onto the eggs.”
By the time the female squid deposits her eggs in a communal seafloor bed, at least three males have had a chance to fertilize them. Hanlon suspects that the big males fertilize the most eggs because their sperm usually have the first chance.
“Squid have been getting fished harder over the past five years,” he says. “If the fishing selectively picks large males, then you have to worry. But it’s good to know these animals have a very robust mating system.”
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