The birds and the bees have a lot to teach us

The birds and the bees have a lot to teach us
Sharon Begley
Wall Street Journal, Feb. 10, 2006

Cole Porter knew that "birds do it, bees do it," but how they (and other creatures) do it makes human mating rituals, even those that will be in full flower on Valentine's Day, look downright tame.

A man who worries about keeping his sweetie faithful after a V-Day interlude, for instance, might learn from the cricket approach: Keep her mouth full.

Male crickets are just as intent as their human counterparts on keeping their mate from leaping into a rival's embrace. But a female cricket, like females of many species, can benefit from promiscuity: By having offspring with different dads, she can increase her kids' genetic diversity, improving the odds that some will survive no matter what conditions they encounter. "From the female's point of view," says biologist Scott Sakaluk of Illinois State University, Normal, "it pays to hedge your bets by mating with as many males as you can."

But a female's mate-til-she-drops strategy reduces her mate's shot at paternity. Every time a rival's sperm reaches her eggs, his chance of becoming a dad declines.

The male's goal, then, is female fidelity; the female's, infidelity. Because of that clash, crickets have developed an arsenal of weapons to thwart the strategy of the opposite sex. Male crickets practice mate guarding, for instance. But that is merely their opening shot.

They also wrap the package of sperm they deposit outside the female's abdomen in a gooey blob, which she peels off and eats. "If he can keep her preoccupied with eating, she can't reach around with her mandibles and remove the sperm," says Prof. Sakaluk. While she chows down, the sperm flow out and fulfill their destiny.

To further improve their odds of paternity, male decorated crickets (their actual name) slip a little something extra into the wrapping: an antiaphrodisiac. "When we fed these nuptial gifts to female house crickets, they were far less eager to mate," says Prof. Sakaluk. It leaves them so not-in-the-mood you could almost hear them chirping, "Not tonight, dear, I have a headache."

But the libido-deadening chemical, still unidentified, has no effect on female decorated crickets, just house crickets. The former have apparently evolved immunity to the males' trick, the Illinois scientists report in the journal American Naturalist. Why, then, do males bother spiking their gift with an antiaphrodisiac? "It probably also stimulates her appetite, so he can ensure she eats after mating and doesn't pull off his sperm package," says Prof. Sakaluk. "It's an unending arms race in a battle of the sexes."

Male swordtail fish have a more aesthetic mating strategy. Their showy fin, like the peacock's tail, supposedly evolved because it attracts females. Some scientists have gone further, claiming that these displays of male pulchritude are also signs of health. The idea is that both tail and sword take so much energy to maintain that only the healthiest hunks manage it. Ergo, well-endowed guys mated more and left more offspring than their drab peers, passing down the gene for these displays. The trait thus spread through the gene pool.

In good news for males lacking what females supposedly want, however, biologists keep shooting holes in this theory. For one study, biologist Gil Rosenthal of Texas A&M University, College Station, exploited a convenient propensity of swordtails. "These fish are just as dumb as we are, and will watch TV for hours," he says.

He and colleague Bob Wong showed females videos of computer-generated males with swords digitally added or erased, then measured how long females spent hanging out by each kind of male. (That has been shown to predict whether a female will sidle up to a real male with that attribute.) Result: Female swordtails preferred the swordless male. Traits that were once presumably favored by sexual selection can, it seems, fall out of favor.

"The females don't prefer swords," says Prof Rosenthal. "They just like size. Our current thinking is that swords and most other sexually dimorphic traits are empty symbols. They're attractive because they're attractive, not because they're signs of genetic superiority. In some cases, being attractive actually lets a male be genetically inferior," because as long as he gets the girl, he can fall short on other measures and still win in the battle for survival of the fittest.

Symmetric features, too, are sexually alluring, supposedly because they signal biological fitness. But as scientists showed last year, the older a female swordtail, the less she lets her pretty little head be turned by a male's symmetric stripes. These ladies preferred asymmetric males.

In the world of humans, a lot of silliness has been written about men's preference for women with Victoria's Secret figures or symmetric faces (something women supposedly prefer in men, too). That preference is wired into male DNA, goes the claim, because the traits reflect the genetic superiority of their female owner - fertility, health, whatever. But there is no evidence for that, and animal studies show the opposite: Sexually attractive traits are rarely a sign of genetic fitness.

"Attractive traits don't necessarily signal anything reliable about males," says Prof. Sakaluk, who could probably make a killing with a T-shirt version of that ... especially starting Feb. 15.