Biologists used to believe that alpha males got all the ladies, thus proving that male domination of women was "natural." But with a little more observation, they realized this wasn't true. The craftiest males, known as "sneaker males," get a surprising amount of sex from a surprisingly happy female population.
An octopus male will spend ten days fighting off the competition for his mate. He will sometimes fight while actually mating with her. (It is tragic that we haven't got this on film.) Although he prefers a large female, he won't object if a couple of small females visit his lady. Sometimes he'll even try to mate with them. When he does, he may find out that he's actually mating with another male.
Small male octopuses will change their color and hide their mating arms to slip past guard males to mate with a female. This is a common deception among cephalopods. Small male cuttlefish will up the stakes by impersonating a female and fighting to the bottom of a mating pile in order to mate with the single female, all while surrounded by larger fighting males.
The deception is common on land as well as in the sea. Side-blotch lizards will develop vivid yellow patches on the sides of their throats in order to impersonate a female and travel through territory guarded by larger males. Salamanders go even farther. Small males will court larger male salamanders, get their sperm, and destroy it. Possibly while cackling.
Then there are the silent sneakers. When the day is full of birdsong and the night is full of the calls of frogs and crickets, not everyone is doing their share. Calling out loudly into the night makes one a target not just for other males, but for predators. Some males quietly get close to a calling male, and mate with any female the calling male attracts. If the calling male happens to suffer a horrible death by owl, well, the sneaker males lives to mate again.
Sneakers can leave aside the cunning and maintain a strong work ethic. Dung beetles build underground dens for their mates, and guard the front entrance. Any male not up to fighting can compensate with nothing more that hard work and a knowledge of geometry. They get out of sight of the guard male and build tunnels down to heavily guarded main tunnel, mating with the female inside while the fighting male guards the front.
So far, the difference between fighting males and satellite males has been one of technique. The sneaker males can be smaller, but they're not physically different from other males. This isn't always the case.
Chinook salmon swim up river every year to spawn. Two kinds of males make the trip. Jacks are small, slender fish that sexually mature fast without putting on bulk. Hooknoses mature slowly, spending more time in the ocean feeding and fattening up. The difference between the two is dramatic, as is the difference between their technique. Hooknoses are big and bulky, and can fight off other males, but when it comes down to it, maneuverability is key. Jacks can dart in at a crucial moment, releasing their sperm and fertilizing the eggs the hooknose fought for.
One of the more startling examples of the two types of males is in the Sumatran orangutan. The species is famous for male bimaturism. Some males mature fast, developing their bodies and growing the distinctive folds, or flanges, on the sides of their faces. Other males keep a juvenile look, sometimes for as long as twenty years after becoming sexually mature. These juvenile-looking males can get chased out of a territory by a mature male, but much of the time they're ignored. Biologists thought that this was a typical sneaker strategy. The unflanged males looked too young to be worth fighting. As researches became more familiar with the habits of the orangutans they realized that flanged and unflanged males don't look for mates the same way. Confident in their ability, the large and mature flanged males sat in trees and called for mates. Unflanged males went on the move, looking for unattached females. So two males of the same species not only had different body types, but completely different behaviors.
The less mature orangutans have less luck with the ladies. Female orangutans show clear preference for flanged males, and will sometimes fight unflanged males. Still, enough of the immature-looking males pass on their genes to keep the line going. And they are on the unsuccessful end of the sneaker male spectrum.
In salmon, jacks far outdistance hooknoses, for many reasons. First, their sperm seems to be more potent. Secondly, it's much more potent with certain female eggs, meaning that some females might naturally lay eggs more receptive to sperm from the sneaker males, or they might be able to manipulate their eggs' receptivity for types of sperm. By maturing faster than hooknoses, jacks spend less time in the dangerous ocean, getting their genetic chances dashed when they're eaten by a shark. And then there are humans, who, when fishing, prefer catching big hooknoses to little jacks, and weed out the larger fish.
Never underestimate the power of female choice. In one experiment, researchers found that females were more likely to get close to the loser of a fight between males than the winner. This may have been because the winner tended to peck her and pull out her feathers. Although it might be nice to have the protection of a super-aggressive male for one's eggs, there are drawbacks to a big, violent mate.
What's important to remember is males aren't the only ones who benefit, genetically speaking, by mating with as many different partners as possible. If only dominant males got to mate, then a female should only gamble her genes on the dominant male. There's no reason to risk life and limb, and waste time and energy, birthing and raising the offspring of a male whose genes make it unlikely that his children will reproduce. Once it becomes clear that sneaker males represent a valid way to survive and reproduce, females have as much reason to hedge their bets as males do. They can choose one or the other, or choose to mate with both.
[Via Evolution's Dating Game and Mating Game, Close Encounters of the Sneaky Kind, Male Bimaturism and Reproductive Success in Sumatran Orangutans, Sneaker Jack Males Outperform Dominant Hooknose Males in Sperm Competition.]