Why Some Males Evolved to Be Small and Sneaky

Bigger males may get a lot of attention, but sometimes being smaller—and sneakier—is more successful when it comes to mating.

In the East African cichlid fish, Lamprologus callipterus, males come in two sizes: giants or dwarves that are 40 times smaller than their beefier rivals. (Watch a video of male cichlid fish fighting.)

It’s an example of male polymorphism, a phenomenon in which males of the same species take different forms. Though people vary in height, men don’t come in two different sizes like the cichlids. Several research studies suggest that tall men—those over 5’7″—are more successful in dating and in their careers—but they get divorced at higher rates.

But the variation in L. callipterus, which are found only in Lake Tanganyika (map), is “the most extreme there is,” said Michael Taborsky, co-director of the Institute of Ecology and Evolution at the University of Bern, Switzerland. “It’s an enormous size difference.”

In a new study, published September 17 in the Proceedings of the Royal Society B, Taborsky and his team linked this gulf in size to the female’s unusual habit of laying eggs in empty snail shells.

To attract females, the giant males collect hundreds of these shells, using their mouths to create nesting sites. But while their hefty build is ideal for lugging about the heavy shells and chasing off rivals, the giants can’t access the chambers of their female harem, instead releasing their sperm outside the shell, Taborsky explained. (Also see “Small Squid Have Bigger Sperm—And Their Own Sex Position.”)

Watch a video of male East African cichlids lifting shells.

Here’s where the sneaky dwarf comes in. Measuring just 3.4 centimeters nose to tail, the fish darts into shells, wriggles past the female into the inner whorl of the shell, and fertilizes her eggs. And because the dwarfs can get so close, they’re more successful at fertilizing the eggs and fathering offspring than the alpha males are.

The study discovered that the two male sizes are determined by a gene on the male sex chromosome—the first time this inheritance mechanism has been clearly demonstrated for polymorphic male animals, Taborsky said.

A photo of a Cichlids fish
The cichlid (pictured) is a colorful fish. An African species L. callipterus (not pictured) has two sizes of males. Photograph by David & Micha Sheldon, Corbis

Dwarf cichlids aren’t the only clever little guys in the animal world: Here are some others that use so-called sneaker strategies to get one over on the alphas.

Cross-Dressing Birds

Male ruffs (Philomachus pugnax), found across Europe and Asia, have a cross-dresser among them—a bird that mimics females to get close enough to mate.

Known as a faeder, it does away with the fancy breeding plumage of the highly aggressive, territorial males and “satellite males” that lurk on the fringes.

Territorial males not only tolerate faeders, they even mate with them—either because they haven’t figured out the imposters’ disguise or, scientists suspect, to attract genuine females to their area. (Also see “7 Gender-Altering Animals.”)

Either way, faeders get to mate without being chased or attacked.

A male ruff displays his breeding plumage in 2008. Photograph by Holger Ehlers, Alamy

As with the cichlid male dwarf, this sneaker morph is rare in ruffs—they make up about one percent of the male population.

David Lank, a behavioral ecologist at Simon Fraser University in British Columbia, explained that these sneakers need to be rare for their mating strategy to work.

“If there are too many ‘sneakers,’ they complete too strongly with each other for the ‘sneaker niche,’ and each one does less well, and there are fewer in the next generation,” Lank, who wasn’t involved in the new cichlid study, said in an email.

Morphing Lizards

Male polymorphism can get complicated, as in the case of the common side-blotched lizard (Uta stansburiana), a North American species in which males come in three alternating colors.

The ultra-dominant, promiscuous males are marked orange; blue signals the stay-at-home, monogamous types; and the sneaky sorts mimic the yellow coloration of females.

A photo of a side-botched lizard
A side-blotched lizard along the Colorado River. Photograph by Norbert Wu, Science Faction/Corbis

The occurrence of these morphs fluctuates due to their different mating strategies. For instance, orange males steal females from the blues, but lose out to the cross-dressing yellow males, but blues aren’t fooled by the yellows, and so on. (Related: “Wild Romance: Weird Animal Courtship and Mating Rituals.”)

Such systems have complex dynamics, Lank said. Each type “does best depending on the relative frequencies of all three morphs,” which leads to cycles in which one or another gains the upper hand.

Hornless Beetles

Sneaker males of the taurus scarab (Onthophagus taurus), a species of North American dung beetle, have a smart strategy to avoid competition with large males guarding entrances to female nests: The sneakers lack horns, so they can tunnel underground to get to the females. (Read another Weird & Wild post on why dung beetles dance.)

By losing their fighting horns and being smaller, they not only tunnel more effectively, but also can afford to put more energy into growing larger sex organs than their heavily armed rivals.

Now that really is sneaky.


Meet the Author
James Owen is a journalist and author based in Stockholm, Sweden. After cutting his teeth on the news and features desks of several UK newspapers, he struck out as a freelance writer, specializing in life sciences and natural history. His fish biography 'Trout' (Reaktion Books) was published in 2012.