In what has been described as a profound example of evolution, paper wasps have developed the ability to recognise faces.
To the average insect, one individual just looks like another, but one wasp species has evolved the ability to recognize individual faces among their peers – something that most other insects cannot do. The development could explain how paper wasps have learned to work together. But, how did complex cognition evolve in just this species?
A team led by Cornell University researchers used population genomics to study the evolution of cognition in the Northern paper wasp, Polistes fuscatus. The research suggests the wasps’ increasing intelligence provided an evolutionary advantage and sheds light on how intelligence evolves in general, which has implications for many other species – including humans.
“The really surprising conclusion here is that the most intense selection pressures in the recent history of these wasps, has not been dealing with climate, catching food or parasites, but getting better at dealing with each other,” says Michael Sheehan, professor of neurobiology and behavior, and senior author on the paper. “That’s pretty profound.”
The team’s research indicates that these facial recognition abilities have evolved rapidly other the last 1000 years, thus conferring a massive intelligence boost and, in turn, a huge evolutionary advantage.
Many vertebrate animals can recognize individual faces, at least in some circumstances, but among insects, facial recognition is quite uncommon. This study explored how and when this ability evolved by analyzing patterns of genetic variations within species.
“The big question we want to explore is how complex traits evolve. What is the mode and tempo of cognitive evolution?” explains Sheehan.”It’s kind of like 23andMe, but with paper wasps.”
Didn’t I sting you already?
The few species of insects that can recognize faces share one trait: communal societies with multiple queens. In communal groups with a single queen, like honeybee colonies, the roles are clear, and each individual knows its place. But paper wasps may have five or more queens in one nest and facial recognition helps these queens negotiate with one another.
The queens form a hierarchy, with the dominant queen producing most of the offspring. Subordinate queens can stay and lay a few eggs or leave to build their own nests. But smaller nests are more likely to be attacked, get stolen or die off.
“If you’re a subordinate in the group, you’re giving up a lot of chance to lay eggs. There are benefits to working in a group but also costs to the individual,” Sheehan says. “In these societies where multiple queens are interacting with one another, that’s where recognition becomes so useful.”
In their battle for dominance, queens fight with one another. By recognizing each other’s faces, the queens can keep track of who they’ve already beaten, or been beaten by. This confers an evolutionary advantage as the recognition of these previous squabbles lessens aggression in the nest.
To study the evolutionary history of the wasps, Sheehan and his colleagues assembled genomes for Polistes fuscatus and two of its closest relatives. When they looked at the genetic variation across the wasps’ genomes, they were searching for DNA signatures that showed patterns of recent positive selection. When positive selection is strong and recent, it leaves a distinct mark, appearing as a long stretch of DNA with little variation among individuals in the population.
“We were looking for sections of DNA that lack diversity,” Sheehan explains. “That suggests there are times when a new mutation appears that’s so beneficial, it sweeps the population. The longer the stretch of DNA lacking diversity, the more recent and intense selection would have to be.”
The analysis revealed that the strongest signatures of selection were by genes involved in insect vision, learning and memory – all traits involved in facial recognition.
To contextualize their findings, the researchers performed the same analyses on two closely related paper wasp species that don’t recognize faces. Those species did not show strong patterns of selection on learning or memory, bolstering the conclusion that individual recognition, a trait unique to P. fuscatus, has been responsible for the distinctive pattern of selection.
“Our finding indicated that cognitive evolution is not necessarily incremental,” Sheehan said. “There are mutations happening that cause big shifts. This suggests the possibility that rapid adaptation of cognitive ability could have been important in other species as well–such as language in humans.”
Original research: Sara E. Miller, Andrew W. Legan, Michael T. Henshaw, et al, ‘Evolutionary dynamics of recent selection on cognitive abilities,’ (2020), https://www.pnas.org/content/early/2020/01/23/1918592117