A recent study from the University of Michigan provides the first evidence of transitive inference, the ability to use known relationships to close unknown relationships in an animal without a spine: the lower paper wasp.
For thousands of years, transitive inference has been a hallmark of human deductive forces, a form of logical reasoning used for inferences: if A is greater than B and B is greater than C, then A is greater than C.
But in recent decades, vertebrates, including monkeys, birds and fish have demonstrated the ability to use transitive inference.
The only published study investigating TI in invertebrates found that honey bees were not up to the task. One possible explanation for this result is that the honeybee's small nervous system imposes cognitive constraints that prevent these insects from making a transitive inference.
Paper wasps have a nervous system that is about the same size ̵
To find out, Tibbetts and their colleagues have tested whether two common types of paper wasps Polistes dominula and Polistes metricus were able to solve a transitive inference problem. The results of the team will be published online on May 8 in the journal Biology Letters .
"This study provides more and more evidence that the insects' miniature nervous system does not limit sophisticated behavior," he told Tibbetts, a professor in the Department of Ecology and Evolutionary Biology.
"We do not say wasps use logical deduction to solve this problem, but they seem to use known relationships to draw conclusions about unknown relationships," Tibbetts said. "Our findings suggest that the ability to handle complex behaviors may be determined by the social environment in which behavior is beneficial and not strictly limited by brain size."
To test TI, Tibbetts and her colleagues first collected Wasp queens from paper from several locations around Ann Arbor, Michigan.
Individual wasps were trained in the laboratory to distinguish color pairs, so-called premise pairs. One color in each pair was associated with a slight electric shock, the other not.
"I was really surprised at how quickly wasps learned the premise pairs," said Tibbetts, who has studied the behavior of paper wasps for 20 years.
Later, the wasps were presented with unknown color pairs and they had to choose between the colors. The wasps were able to organize information in an implicit hierarchy and used transitive inference to choose between new pairs, Tibbetts said.
"I thought wasps could be confused, just like bees," she said. "But they had no trouble finding out that a certain color was safe in some situations and not safe in other situations."
Why Do Wasps and Honey Bees, Both of Which Have a Smaller Brain Than a Rice Grain, So Different From Transitive Inference Tests? One possibility is that different types of cognitive ability are favored in bees and wasps because they show different social behaviors.
A honey bee colony has a single queen and several equal female workers. In contrast, paper wasp colonies have several reproductive women known as founders. The founders compete with their rivals and form linear dominance hierarchies.
The rank of a wasp in the hierarchy determines the proportion of reproduction, work and food. Transitive inference could allow wasps to quickly draw conclusions about novel social relationships.
The same capabilities could allow female paper wasps to spontaneously organize information during transitive inference tests, the researchers said.
For thousands of years, transitive inference has been a hallmark of human perception, and it has been assumed to be based on logical deductions. More recently, some researchers have asked whether TI requires higher-order justification or can be solved with simpler rules.
The study by Tibbetts and her colleagues shows that paper wasps can build and manipulate an implicit hierarchy. However, the exact mechanisms underlying this ability are not claimed.
In earlier studies, Tibbetts and her colleagues showed that paper wasps recognize individuals of their species by varying their facial markings and behave more aggressively towards wasps with unfamiliar behavior.
Researchers have also shown that paper wasps have surprisingly long memories and their behavior is based on what remind them of previous social interactions with other wasps.
The other authors of the new Biology Letters paper – Jorge Agudelo, Sohini Pandit and Jessica Riojas – are students.
The work was supported by the National Science Foundation and the Doris Duke Conservation Scholars Program at the University of Michigan, funded by the Doris Duke Charitable Foundation. All experiments conformed to United States laws and international ethical standards.