The Blotchier The Face, The Better The Wasp

When wasps sporting the high-quality symbol of a blotchy face turned out to be wimps, they got harassed more than wasps whose abilities were honestly reflected by their faces, report researchers.

It's the first conclusive report that animals that don't signal their qualities honestly receive social sanctions. Moreover, it's the first report of such quality signals in insects.

"It's the most conclusive evidence that these dishonest visual signals have a social cost," said Elizabeth A. Tibbetts, a postdoctoral fellow with the Center for Insect Science at the University of Arizona in Tucson. "If you fake it, you'll get beaten up."

She and her co-author James Dale of Simon Fraser University in Burnaby, British Columbia, Canada report their findings in the Nov. 11 issue of the journal Nature.

Many animals sport visible indicators of the bearer's quality. Such signals include the redness of a cardinal or the size of the black spot on a house sparrow's chest.

However, biologists wonder what keeps other animals from cheating by displaying a mark that indicates "I'm great" while actually being just average. Scientists hypothesize that social interactions discourage cheating, but demonstrations of such interactions have been elusive.

Tibbetts noticed that for wasps in the species Polistes dominulus, the facial markings varied among individuals. Because these wasps are social insects that form multi-queen nests, she wondered whether the markings had significance to the wasps.

Researchers already knew that in such nests, the wasps establish a dominance hierarchy by fighting. The winner, the top or alpha wasp, gets to lay more eggs and do less work than the other wasps. To see whether they could detect what signaled an alpha wasp, Tibbetts and Dale decided to stage wasp fights.

She captured wild wasps and brought them back to the lab. There she paired up wasps of equal weight, put them in small plastic container and let them fight.

The wasps duked it out using a combination of pacing about, having staring contests and grappling with one another. It took the wasps between 5 minutes and two hours to sort out their differences.

By analyzing videotapes of 61 wasp fights, the researchers found that the winning wasps generally had more broken-up, spotty or wavy black patterns on their faces' yellow center.

But if the subordinate, or beta, wasp also had a broken or mottled facial pattern, the alpha wasp was more likely to keep hassling the subordinate wasp. So having a "dishonest" face, one that signals being higher quality than you are, is a liability in the wasp world, Tibbetts said.

As a final test of their hypothesis, the researchers decided to stage some fights where one wasp had been experimentally altered so her face didn't reflect her true quality.

After chilling wasps in a refrigerator, Tibbetts used a toothpick to apply Testor's model paint to their faces. Some wasps were given blotchier faces, some wasps had blotches covered up, and some wasps were just handled and had paint put on their existing blotches.

Again, the team paired up wasps by size and let 'em have at it.

The wasps established dominance hierarchies, but in the cases where one wasp had a dishonest face – one that didn't match its original face – the fighting was more intense.

In some cases, dominance was established and then fighting continued and the hierarchy flipped – something that never happened in wasp fights with unaltered wasps. Even if the dominance hierarchy was maintained, the unaltered wasp was much more likely to continue to harass the altered wasp.

"Changing the face interfered with their establishment of a dominance hierarchy," said Tibbetts. "Our best explanation is that there's some other information about wasp quality that doesn't match the altered face."

They hypothesized that there are some other signals, either chemical or behavioral, that wasps use to determine one another's quality. When a wasp transmits mixed signals, it gets punished.

"That kind of aggression has lasting repercussions," she said. "They have less time to feed and to take care of their offspring."

Dale said, "Wasps have really sophisticated visual signaling systems. We're just starting to get a window into the kinds of messages they're telling each other."

Tibbetts' next step is investigating how the wasps' facial patterns affect other aspects of their social interactions.

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The research was funded by the National Science Foundation, the National Institutes of Health and the Natural Sciences and Engineering Research Council of Canada.