A team of researchers from the University of Michigan has found evidence of transitive inference — a form of logical reasoning that involves using known relationships to infer unknown relationships (if A is greater than B, and B is greater than C, then A is greater than C) — in two species of paper wasps: the European paper wasp (Polistes dominula) and the metricus 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 behaviors.
In recent years, vertebrate animals including monkeys, birds and fish have demonstrated the ability to use transitive inference.
The only published study that assessed transitive inference in invertebrates found that honeybees weren’t up to the task. One possible explanation for that result is that the small nervous system of honeybees imposes cognitive constraints that prevent those insects from conducting transitive inference.
Paper wasps have a nervous system roughly the same size — about one million neurons — as honeybees, but they exhibit a type complex social behavior not seen in honeybee colonies.
University of Michigan’s Professor Elizabeth Tibbetts and colleagues wondered if paper wasps’ social skills could enable them to succeed where honeybees had failed.
To find out, they tested whether Polistes dominula and P. metricus wasps could solve a transitive inference problem.
“We’re not saying that wasps used logical deduction to solve this problem, but they seem to use known relationships to make inferences about unknown relationships,” Professor Tibbetts said.
“Our findings suggest that the capacity for complex behavior may be shaped by the social environment in which behaviors are beneficial, rather than being strictly limited by brain size.”
To test for transitive inference, the team first collected paper wasp queens from several locations around Ann Arbor, Michigan.
In the lab, individual wasps were trained to discriminate between pairs of colors called premise pairs. One color in each pair was associated with a mild electric shock, and the other was not.
Later, the wasps were presented with paired colors that were unfamiliar to them, and they had to choose between the colors. The wasps were able to organize information into an implicit hierarchy and used transitive inference to choose between novel pairs.
“I thought wasps might get confused, just like bees. But they had no trouble figuring out that a particular color was safe in some situations and not safe in other situations,” Professor Tibbetts said.
So, why do wasps and honeybees perform so differently on transitive inference tests?
One possibility is that different types of cognitive abilities are favored in bees and wasps because they display different social behaviors.
A honeybee colony has a single queen and multiple equally ranked female workers. In contrast, paper wasp colonies have several reproductive females known as foundresses. The foundresses compete with their rivals and form linear dominance hierarchies.
A wasp’s rank in the hierarchy determines shares of reproduction, work and food. Transitive inference could allow wasps to rapidly make deductions about novel social relationships.
“That same skill set may enable 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