FLICKR, ANIL JADHAV
American cockroaches (Periplaneta americana) behave according the social expectations of a group, even though they may vary in individual levels of boldness, according to a study published today (February 4) in Proceedings of the Royal Society B.
Personality—defined as a persistent behavior such as sociability, aggression, or daring—had previously been shown in a variety of invertebrates such as spiders and octopi, but had not yet been demonstrated in cockroaches. Since the insects are social but not constrained to a leader-driven hierarchy, Isaac Planas-Sitjà and his colleagues at the Université libre de Bruxelles in Belgium decided to use P. americana to study the differences between individual and group personality.
The researchers glued radio frequency tags on more than 300 four-month-old male roaches sorted into groups of 16. Over the course of a week, the groups of light-averse insects spent most of their time in dark, with the exception of three evenly spaced three-hour sessions in an enclosed and brightly lit test environment that had two shaded areas for shelter. Some cockroaches were consistently shy and dashed to the shaded areas as soon as they were placed in the environment, while others took their time exploring the well-lit area during each of the trials. By the end of each trial, however, all 16 members of the group ended up under the same shelter. “There is a collective dynamic—a social influence—that dilutes the individual personality differences,” Planas-Sitjà told Science. “So in the group, you end up with a similar behavior in everyone.”