Collective resilience in a disturbed environment: stability of the activity rhythm and group personality in Periplaneta americana

Studies on the use of aggregation sites, or communal roosts, found that these roosts have high stability but that individuals will migrate to other sites when the original site is disturbed or otherwise no longer suitable. In this study, the aggregation dynamics of groups of Periplaneta americana were examined without interruption for 5 days and 4 nights. Our results showed that groups inside an undisturbed aggregation site presented stable group personalities and choice in aggregation site. The individuals that were aggregated in a site that was repeatedly disturbed by a lighting stimulus during their resting period not only exhibited stability in their group personalities but also a resistance to the disturbance, which allowed the initial aggregation site to remain the site of choice for a few days. Regarding the group personalities, we showed that the groups had distinct personalities with respect to the total amount of time spent outside of aggregation sites and at the sources during their active period and the time spent sheltered during their resting period. For the reaction to the disturbances, we found that the groups showed distinct personalities between the fraction that fled and the fraction that migrated to the undisturbed site. Our study also showed that although the disturbances were strong enough to trigger fleeing behaviour and induce migration to an undisturbed shelter site, the disturbance did not influence the group’s global activity rhythm.