As unlikely as it may seem, individual cockroaches vary in personality. Now, new research suggests that adult cockroaches may maintain some of the personality traits they developed as youngsters.
“The idea that even insects can show variation in personality may sound a little far-fetched,” says behavioral ecologist Christina Stanley, who led the new research. “But numerous studies across a range of species have now demonstrated that individuals can differ consistently in their responses to certain situations.”
Of these numerous studies, few have investigated how an animal’s personality may shift between different life stages. “If it remains the same across distinct developmental stages, there must be clear advantages to this,” Stanley says.
Insects, which often undergo major physiological changes while molting between life stages, could provide valuable insights into the stability of personality over a lifetime.
Stanley’s team tested consistency of personality in 24 juvenile and 65 adult cockroaches of the species Diploptera punctate. 19 individuals were tested as both youngsters and adults. For each stage, the scientists tested the cockroaches’ personalities twice, with a few days between each round. They focused on three traits: boldness and exploration — which represent risk-taking tendency — and sociality.
In one test, each cockroach explored the surface of a sheet of paper divided into sections, demonstrating exploration and boldness levels. Another test also measured boldness by examining behavior after sudden exposure to bright light. A third test investigated social behavior during interaction with other cockroaches.
Relative to one another, the 19 cockroaches tested at both life stages tended to maintain their individual juvenile boldness and exploration levels as adults. This was in spite of an overall decrease in boldness with age, likely due to changing ecological needs. Within stages, both juvenile and adult individuals maintained consistent levels of boldness between the two rounds of testing. Adults also showed consistent levels of exploration and sociality, while youngsters did not.
Further work with more juveniles would be useful to confirm these results with greater statistical power. Nonetheless, the findings reaffirm the fact that cockroaches do, indeed, have personality.
“Cockroaches are often given a bad press,” Stanley says. “Perhaps the fact they show distinct personality traits will slightly improve their public image!”
Research Article: Stanley CR, Mettke-Hofmann C, Preziosi RF (2017) Personality in the cockroach Diploptera punctata: Evidence for stability across developmental stages despite age effects on boldness. PLoS ONE 12(5): e0176564. https://doi.org/10.1371/journal.pone.0176564
Image Credit: Christina Stanley