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Published: Monday, 4/30/2001

Bluegill sunfish can't trust some males' mating habits

BY JENNI LAIDMAN
BLADE SCIENCE WRITER

Lepomis macrochirus | Bluegill sunfish

When you see a man in heels, hose, and a flouncy dress - say, in a movie - do the words “chick magnet” ever pop into your mind?

Me neither. Even though it seems actors - Kurt Russell, Dustin Hoffman, Jamie Farr, to name a few - wear dresses and makeup more often than many women I know, the phenomenon still hasn't caught on in the singles' bars.

Pity. There's evidence to suggest that looking like a girl can increase mating success.

If you're a fish.

This is kind of a sordid story, so you might want to send the children to bed. Or send them to school. Whatever you do, don't eat them, despite any ideas these fish may provide, or how much you hate going to the grocery store.

Male bluegill sunfish exhibit some unsavory behaviors in their battle for reproductive success. For instance, they've evolved three types of males, and two of them don't play by the rules.

Scientists call the traditional male a “bourgeois” variety. He makes a nest, attracts a female, mates, then guards the embryos against all others. He does everything short of buying a lawnmower to secure his solid-citizen status.

A second variety of male is actually an adult disguised to look like a kid. His strategy is to zip under the mating couple just as the female releases her eggs, adding his sperm to the mixture. Biologists call this hit-and-run master a sneaker male, since he's a heel.

Finally, there are the satellite males. These guys look like girls. They're so convincing, in fact, our homemaker male will tolerate the cross-dresser's presence during mating. To Mr. Nest-in-the-Suburbs, the satellite male looks like My Lucky Day. But the satellite male is really releasing sperm while making kissy faces at his gullible competitor.

This sneaking and drag-swimming isn't just a temporary adaptation for those times when females are scarce. These are permanent behaviors. Sneakers stay sneakers. Satellites keep shopping for shoes, and neither ever changes into a bourgeois males.

In addition to all this mating skullduggery, bluegill sunfish exhibit the usual male mating behavior of fighting with other males. Often, one male will chase another away from his nest full of fertilized eggs, then use the nest to attract females.

All in all, being a male bluegill sunfish is a tortured existence. Susan Faludi should write a book about it. Here's the poor male daily growing more suspicious of the females he wants to mate with, constantly patrolling for sneaky pretend youngsters, and ever pumped to do battle with other bourgeois males. Then, there are the other fish hanging out who find sunfish eggs their kind of caviar. How do these guys find the time to do anything but guard nests? When do they shop? How can they grab a quick moment to forage for lunch?

Turns out, they don't hunt. They snack. On the little embryos in their nest.

Andrew DeWoody, an assistant professor at Purdue University, wanted to see just whom male sunfish were eating. Most of our notions about evolution say that nature favors critters with the most and healthiest babies to carry genes to the next generation. That would suggest that sunfish shouldn't eat their own eggs, but make an omelet with the eggs of their competitors.

Given the fact that some fish species can recognize kin, it's possible they will be picky eaters.

“Oops, Dad spit out little Betty. Take that neighbor kid over there.” Genetic testing only recently revealed that many males guard nests full of someone else's kids, so it's not as though there are no non-relatives available to eat.

Dr. DeWoody applied genetics to determine on whom sunfish were snacking. He used two different sunfish species, each with similar mating habits to the bluegill sunfish. Dr. DeWoody opened their bellies, removed the eggs he found, and looked at certain genetic markers.

And guess what? That's right. Daddy never did spit out little Betty.

In a world where the prized picture of parenthood is the doe that stays with her fawn despite danger, or the King penguin father who saves food for his chicks, nature isn't so sentimental. And, for the sunfish's purposes, it works.

“I would argue selection favors the egg-eating behavior,'' Dr. DeWoody said. “When you do that, you just lose a small percentage of your clutch. The only other option for fish is to leave their nest for forage. If you do that, you have no reproductive success.''



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