NOVA Online | Flying Casanovas | Creature Courtship (2)

Creature Courtship
Part 2 | Back to Part 1

The meek shall inherit

While sexual selection has favored the biggest individuals in species like elephant seals and elk, sometimes tremendous size can work against its owner. Bull elephant seals, for instance, can reach five times the weight of their mates, and among the northern subspecies, roughly one in 1,000 cows dies of suffocation while copulating with such behemoths. Though this death rate is low, Mother Nature appears to have taken notice and placed a possible check on the evolutionary trend toward Brobdingnagian. While beachmasters are battling it out, smaller males are sometimes able to snatch sex from cows apparently willing to forgo the biggest for the craftiest.

Gender-jumper extraordinaire, a clownfish hovers amid the protective arms of a sea anemone.

Biologists have recently identified a similar strategy of trumping the Schwarzeneggers of one's kind in species a fish found in lakes along Africa's Great Rift Valley. The fish in question is the shell-brooding cichlid Lamprologus callipterus. Proportionally, this species boasts the largest males in the animal kingdom; mature males are up to 30 times the size of their mates. These comparatively massive males fill their lake-bottom territories with empty aquatic snail shells. Interested females enter the shells and spawn, while the giants hover outside, spewing sperm all over the place.

These males might seem to have it made, yet L. callipterus features another kind of male, one that goes in for brains over brawn. Looking for all the world like a nonbreeding female, this David swims unmolested into an occupied shell and, unbeknownst to the Goliath hanging around outside, fertilizes the female, ensuring a future for his genes.

The male clown fish has evolved an even more ingenious means of getting the girl: He becomes one. Among clown fish, which form monogamous pairs, the female is heftier than the male, but if she dies or disappears, the male puts on weight, changes sex, and bonds with a new male partner.

Looking good

While gender-jumping is common among fish (though it usually happens in the opposite direction, from female to male), most males in the animal world don't have such a convenient option. And judging from appearances, many males would just as soon not have to grapple with others of their gender. These males eschew Darwin's first kind of sexual selection for his second. On the surface, bright colors, fancy appendages, and flashy displays may seem a kindler, gentler form of competition than that evinced among those built for armed combat. But the drive for success is no less steely.

Striking color combinations are de rigueur among males of many bird species, including this regent bowerbird.

Males in many species attract members of the opposite sex with dazzlingly colored feathers, skin, or other body parts, which put comparatively drab females of the same species to shame. Such color dimorphism is particularly prevalent among birds. Many species show it, from such commonly seen birds as the cardinal to the elusive quetzal, the most strikingly hued bird in the Americas. The males of this species have flaming red crests and emerald tail feathers almost three feet long, neither of which the females possess. That's because such structures—arguably exemplified by the sexual billboard that is the peacock's train in full display—are another attribute males have evolved over the eons to excel in the mating game.

Even the most foppish males seem to realize, however, that beauty is only skin deep, so they combine appearances with action. The cardinal lures the female with a series of calls and gifts of tasty sunflower seeds. The quetzal courts with a painstaking song-and-dance routine. Even the lordly peacock shakes its brilliant billboard for added effect.

Erect and fastidious as a Buckingham Palace guard, a male sage grouse prepares to parade, his head all but lost in a bravura display of brawn.

Holding courtship

Some of these ritualized courtship displays can be quite involved. On the western prairies of North America, for instance, male sage grouse congregate on vast display grounds, where they strut their stuff before females. Mate markets of this sort are common among birds; ornithologists know them as "leks," which comes from a Swedish word for play.

Each sage grouse male is a wonder of pumped-up masculinity. Standing tall on his patch of preferably raised ground, he holds his wings at his sides like medieval shields, puffs out his robust chest of downy white feathers, throws up a daunting array of pointed tail feathers, and begins to stomp vigorously on the ground. (The bird's singular two-step inspired the foot-stomping ceremonial dances of the Sioux Indians.)

Getting worked up, the grouse then takes a few steps, draws back his head, and rapidly deflates a pair of scrotal-like air sacs jutting from his chest. The resulting "plop" can be heard several hundred yards away. At the same time, the bird briskly rubs his breast feathers against the wings at his side, generating a swishing sound. When this sequence is finished, he stands still as a statue for a few moments, then repeats the performance, eager to have nearby hens take notice.

As with elephant seals, the payoff is tremendous for the cock that impresses the most hens. On one such display ground, for example, a single male sage grouse enjoyed fully three fourths of 174 couplings.

One of the most accomplished acrobats in the avian world: the male long-tailed manakin.

Team work

While the sage grouse lek has males fervently competing with one another, the lek of the long-tailed manakin, a diminutive bird found in the rainforests of Costa Rica, is altogether different. In this lek, two male manakins cooperate with each other so that the dominant one of the pair can mate with a smitten female.

The display begins with the two males patiently perched on a horizontal branch near the ground, calling for females with a distinct toe-le-doe whistle. When a female lands on the branch, indicating she's ready to be courted, the two males, which are black with turquoise backs, crimson crowns, and twin tail feathers as long as their bodies, launch into a prolonged acrobatic display, whistling their flute-like call all the while. They step daintily and hop energetically; they somersault and leap-frog; they take turns hovering in the air.

As the tempo picks up, the males emit a buzzing sound, and the female becomes more and more excited. At some critical point in the crescendo, the leading male utters a shrill cry; this is the lesser male's cue to make himself scarce. Alone at last, the vanquisher performs a brief dance before his prize and then quickly mounts her.

The long-tailed manakin presents a rigorous test of Darwin's theory of sexual selection. Not only have males evolved a handsome dress code, including radiant colors and lengthy tail, but they also dance to beat the band. They'll go on sometimes for 20 minutes, proving just how fit they are. On top of that, if the pas de deux is successful, only the lead male gets the spoils. How can the subordinate male's costly extras and exhausting performance possibly help him in the survival of the fittest if he knows even before he begins a dance that he has no chance of mating? Is it all for naught?

Not at all. He learns the ropes, so that when the dominant male dies or becomes less sprightly with age, his apprentice can take over the lek or perhaps form his own. Nature has it all figured out.

Peter Tyson is editor in chief of NOVA Online.

Further reading

A Natural History of Sex: The Ecology and Evolution of Sexual Behavior, by Adrian Forsyth. New York: Scribner's, 1986.

Battle of the Sexes: The Natural History of Sex, by John Sparks. New York: TV Books, 1999.

The Ant and the Peacock: Altruism and Sexual Selection From Darwin to Today, by Helena Cronin. New York: Cambridge University Press, 1991.

Sexual Strategy, by Tim Halliday. Chicago: University of Chicago Press, 1980.

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