Researchers consider these ostentatious male weapons to be honest signals - advertising the owner’s might and fitness accurately. (And sometimes other costs: Male fiddler crabs can only stuff algae in their mouths with one claw.) Studies show that the weapons’ sizes are sensitive to nutrition, parasite load, stress and overall physical condition - and so the healthiest, most fit individuals sport the most impressive weapons. Weapons for showĪs the weapons grow bigger and flashier, they come with the cost of producing and lugging around such big structures. And the most dazzling weapons act largely as deterrents, with actual fights breaking out only when males are closely matched. Indeed, variation in the size of male weaponry is huge, Emlen notes: While overall body size among adult male elk might vary by a factor of 2 at most, their antler racks can vary by a factor of more than 30, he says. Scientists say that this supports the idea that these weapons are built for rivalry - their designs optimized not for destruction but for power struggles. And three: Males of the species compete in one-on-one duels.īut the fighting is almost never to the death and rarely results in serious wounds. Two: It’s possible for access to those resources to successfully be guarded. One: Males must be competing over either resources such as food or over females. The fearsome weapons seem to evolve whenever three criteria are met, Emlen says. Soaring fight music added for dramatic effect! Red deer duel against a gloomy sky as the sun sets over England. If one decides he has the upper hand, he flings his opponent away from the burrow. Dueling males shove and tap on each other’s single, enlarged claw - and, should the fight escalate, they lock claws, secret-handshake style, as if they’re testing the other’s strength. Most species of male fiddler crabs guard their burrows, where mating takes place. Rival males size each other up, and if their horns’ sizes are similarly matched, a face-off ensues and each uses his horns to try to flip, pry and toss his rival off the tree branch. Rhinoceros beetles, named for their rhino-like horns, guard access to the oozes of tree sap that females feed upon before laying eggs. Like the structures, types of combat vary greatly.
But it’s clear that the wild array of weapons evolved to aid successful mating. Scientists still debate the degree to which female choice plays a role in shaping the weapons’ flair and are still trying to figure out what factors drive the diversity of weapon forms seen among even closely related species. It’s such a common theme that Emlen had to persuade his editors to include seven detailed, full-page line drawings in a survey of nature’s weapons that he wrote for the 2008 Annual Review of Ecology, Evolution, and Systematics, featuring more than 280 examples of fantastical spikes, horns, antlers, pincers, tusks, claws, extended jaws, saws and spears. The number and variety of examples argue that evolution has turned to weaponry time and again in the race to reproduce successfully. Even extinct species such as trilobites and dinosaurs sported elaborate projections. Examples of such sexually selected weapons abound throughout the animal kingdom in insects, fish, crustaceans, reptiles and mammals as varied as narwhal, rhinoceros and moose.
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