Before a fight, many animals size up their opponents—however briefly. Even a once-over can provide crucial information about whether to stay and risk injury or turn and flee. Some animals have evolved telltale signs or behaviors that allow them to efficiently judge one another's strength and avoid any unnecessarily costly battles. Deer assess their peers' antlers, and some birds and lizards intimidate one another with prominent patches of color.
But what evolutionary pressures prevent an animal from deceiving its peers by looking like a bully when it's really a pushover? A new study published August 19 in Current Biology suggests that paper wasps control for this kind of deception using social punishment. Wasps beat up phonies.
To help establish stable hierarchies of dominance, highly social paper wasps called Polistes dominulus rely on distinct facial markings—bold black tattoos on their bright yellow faces. Dominant wasps display more fragmented facial patterns than submissive wasps, and the insects use these markings to determine who should submit to whom.
"They're kind of like karate belts for the wasps," says Elizabeth Tibbetts, a biologist at the University of Michigan, Ann Arbor, and lead author of the study. "If someone wears a black belt, they are saying they are a good fighter, but you could imagine someone choosing to wear a belt of any color, even if they're not that good." Wasps can't change their faces at will, Tibbetts points out, but an advantageous mutation could plausibly create cheaters that boast talents they do not have.
To investigate how wasps read one another's faces, Tibbetts turned to some standard laboratory tools—paintbrushes and ink. She painted the faces of one group of paper wasps so that they advertised stronger fighting abilities than they really possessed. For the control group, she simply painted over the markings inherent in the wasps' faces, without changing their patterns. She also gave some wasps a hormone that made them more aggressive and others a hormone that did not change their behavior. Tibbetts then set up a series of duels, each between two wasps that had never met before: one wasp had been manipulated in some way and the other wasp's face and behavior were completely unaltered. She observed each match for two hours, waiting to see who would establish dominance—during which one wasp finally mounts and subdues another.
Any of Tibbetts's manipulations that interfered with the usual facial reflection of fighting abilities also interfered with the wasps' normal social interactions, preventing them from establishing typical social hierarchies. Wasps with gentle faces that behaved aggressively because of the hormone treatment had a lot of trouble convincing their rivals to submit. And the submissive wasps to which Tibbetts applied intimidating makeup were bullied again and again. As soon as their opponents discovered their deception, they were punished.
Tibbetts thinks this kind of social punishment could be particularly useful in long-term contests over valuable resources, during which wasps have the opportunity to repeatedly test the accuracy of their rivals' markings.
"Punishment not only hurts the cheater but provides a benefit to the punisher," Tibbetts says. "Over the course of the interaction, the punisher realizes that maybe their opponent's signal is not accurate. If they trusted the signal, they would have lost out."
*Clarification (8/30/10): The headline was edited after posting. It originally identified paper wasps as painted paper wasps.