A team of researchers at the University of Michigan has found evidence of transitive inference, a form of logical reasoning that involves the use of known relationships to infer unknown relationships (if A is greater than B and B is greater than C, then A is greater C) – in two species of paper wasps: the European paper wasp (Polistes dominula) and the metric paper wasp (Polistes metricus). The study, published in the journal. Biology letters, contributes to a growing body of evidence that the miniature nervous systems of insects do not limit sophisticated behavior.
The European paper wasp (Polistes dominula). Image credit: Adrian Benko / CC BY-SA 3.0.
In recent years, vertebrate animals, including monkeys, birds and fish, have demonstrated the ability to use transitive inference.
The only published study that evaluated transitive inference in invertebrates found that bees were not up to the task. One possible explanation for this result is that the small nervous system of bees imposes cognitive limitations that prevent these insects from making transitive inferences.
Paper wasps have a nervous system about the same size, about a million neurons, like bees, but they exhibit a kind of complex social behavior that is not seen in bee colonies.
Professor Elizabeth Tibbetts of the University of Michigan and her colleagues wondered if the paper wasps' social skills could enable them to succeed where bees had failed.
To find out, they tried if Polistes dominula Y P. metricus Wasps could solve a transitive inference problem.
"We are not saying that wasps used logical deduction to solve this problem, but they seem to use known relationships to make inferences about unknown relationships," said Professor Tibbetts.
"Our findings suggest that the ability for complex behavior may be determined by the social environment in which the behaviors are beneficial, rather than being strictly limited by the size of the brain."
To test the transitive inference, the team first collected paper wasp queens from various locations around Ann Arbor, Michigan.
In the laboratory, the individual wasps were trained to discriminate between pairs of colors called pairs of premises. One color in each pair was badociated with a slight electric shock and the other was not.
Later, the wasps were presented with matching colors that were unfamiliar to them, and they had to choose between the colors. Wasps were able to organize information into an implicit hierarchy and used transitive inference to choose between new pairs.
"I thought the wasps could get confused, like bees." But they had no trouble realizing that a particular color was safe in some situations and not in others, "said Professor Tibbetts.
So, why do wasps and bees perform so differently in transitive inference tests?
One possibility is that different types of cognitive abilities are favored in bees and wasps because they show different social behaviors.
A bee colony has a single queen and multiple workers of equal rank. In contrast, paper wasps colonies have several reproductive females known as founders. The founders compete with their rivals and form hierarchies of linear dominance.
The rank of a wasp in the hierarchy determines the percentages of reproduction, work and food. The transitive inference could allow wasps to quickly make deductions about new social relationships.
"That same set of skills can allow female paper wasps to spontaneously organize information during transitive inference tests," the scientists said.
Elizabeth A. Tibbetts et al. 2019. Transitive inference in Polistes paper wasps Biology letters 15 (5); doi: 10.1098 / rsbl.2019.0015