A team of scientists at the University of Michigan has observed the first instance of transitive inference in invertebrates among paper wasps.

In a study featured in the journal Biology Letters, evolutionary biologist Elizabeth Tibbetts and her colleagues sought to prove whether invertebrates or animals that do not have backbones or bony skeletons are capable of logical reasoning.

The researchers focused on a particular form of thinking known as transitive inference (TI), where organisms use known relationships to try to identify unknown ones. An example of this is if A > B, B > C, C > D, and D > E, then it can be said that B > D.

Instances of TI have mostly been seen among vertebrates, such as birds, fish, and monkeys.

Scientists tried to observe transitive inference in invertebrates, specifically honeybees, during an earlier study. However, they failed to do so, likely because the nervous system of the insects was too small to allow TI.

Transitive Inference In Paper Wasps

For their experiment, Tibbetts and her team chose to study paper wasps because of their similar nervous system to that of honeybees. The insects also possess complex social skills, which may be able to show transitive inference.

The researchers collected specimens of paper wasp queens from different locations in Ann Arbor, Michigan. They focused on two species of the insects: the Polistes dominula and the Polistes metricus.

The paper wasps were trained in a laboratory to identify certain pairs of colors known as premise pairs. The team associated one of the colors in each pair with a mild electric shock.

Not only were they able to learn the premise pairs quickly, but they were able to do so accurately as well.

When the paper wasps were later made to pick out colors from pairs that were not familiar to them, they were still able to do so. The researchers said the insects organized the information using an implicit hierarchy then identified the correct pairs through the help of TI.

Tibbetts said they thought the paper wasps would get confused, much like the honeybees during the previous study. However, the insects had no problems choosing which colors were safe in certain situations and which ones were not in other situations.

Differences In Social Behavior Between Wasps And Bees

The cognitive ability in paper wasps may be explained by the differences in social behaviors between them and their honeybee counterparts.

Colonies of honeybees are governed by a single queen bee and operated by numerous equally ranked workers. Meanwhile, colonies of wasps are ruled by reproductive females called foundresses. These female wasps compete with each other, forming several linear dominance hierarchies.

An individual wasp's standing in the hierarchy determines just how much share it has in the colony's work, food, and reproduction. It is likely that the insects use TI to identify novel social relationships between other members of their hive.

The paper wasps in the experiment may have also used this form of cognitive skill to organize different information spontaneously during the transitive inference tests, according to the researchers.

The study's findings may help answer the question among researchers on whether higher-order reasoning is needed for TI or if the skill can be carried out by following simple rules.

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