Paper wasps that lie to their mates get a right kicking, research finds

Trial by combat and toothpick-applied war paint

Cheating is an unforgivable offence for paper wasps and has a direct effect on their hormones, according to new research published in the Proceedings of the National Academy of Sciences.

Paper wasps (polistes dominulus) have elongated bodies that can reach an inch in size. They build their nests by chewing plant and wood fibres which they glue together with their saliva.

Unlike hornets or yellow jackets, paper wasps are not particularly aggressive by nature. If their nests are threatened, however, they will be ready to attack any intruders.

Researchers at the University of Michigan decided to study the insects' behaviour at the height of their aggression. Spring is a time when wars between paper wasp queens begin.

Roving queens attempt to take over existing nests by challenging its queen. If she is successful in overthrowing the old queen, the empire is hers. If she is unsuccessful, however, the old queen can continue ruling whilst she is banished or executed.

The mark of a good fighter lies on a paper wasp’s face. Wasps with more irregular black spots on their faces are stronger and win more fights. Rivals can avoid unnecessary brawls with stronger wasps by examining these marks.

To investigate the effects of cheating, researchers fabricated black marks on a queen paper wasp’s face with paint and made them battle other wasps with unpainted faces.

Elizabeth Tibbetts, lead author of the study and associate professor in the Department of Ecology and Evolutionary Biology at the University of Michigan, told The Register she used toothpicks to dab paint on the wasps’ faces.

The queen wasps were held in isolation in their nests and fed a diet of water and rock sugar for two days before they were pushed into the battle ring. A painted and an unpainted wasp of similar size were pitted against each other, and each fight was recorded.

Aggressive behaviour was scored based on the number of mounts, bites, grapples and stings observed during combat.

After 65 matches, the queens were drained of their blood straight away so that researchers could detect the changes in levels of juvenile hormone, also known as JH – a hormone that has similar effects to testosterone and makes the queens more aggressive and competitive. In 37 fights the wasps were left in the ring for two hours; in 28 of the matches, the wasps were held in isolation for three hours before being bled.

Researchers found that queen wasps with painted faces that signalled an inaccurate measure of their strength were punished more harshly. Their opponent was more aggressive and after the fight they had increased levels of JH, whilst the ‘cheaters’ had decreased levels.

In wasps, JH influences social rank and determines the likelihood of them reproducing. Only queens can lay eggs, whilst lower-ranking female worker wasps can not.

“JH is involved in competition. And for wasps that lose, they are less likely to be successful in setting up their hive and less likely to be able to defend it,” said Tibbetts.

The evolutionary advantage of changing JH levels are unknown. Although having higher levels of JH increases a wasp’s power, it also reduces the effectiveness of its immune system. Similarly to testosterone, high levels of JH can weaken the immune system.

“Animals don’t have rules and laws, yet they don’t cheat,” Tibbets said. The researchers believe that their study shows wasps that cheat with dishonest signals are aggressively punished, and this punishment has negative lasting effects on their biology and those they interact with.

The cost of cheating could explain why most animals have maintained “honest communication through evolutionary time”.

The paper, Socially selected ornaments influence hormone titers of signalers and receivers has been accepted by the Proceedings of the National Academy of Sciences and will be published later this week.

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