Could Species Segregation be a Consequence of Aggregation Processes? Example of Periplaneta americana (L.) and P. fuliginosa (Serville)

Our aim was to show how interindividual interactions, based on specific recognition signals that induce aggregation, can lead to the emergence of a segregation pattern between species. Groups including two cockroach species, Periplaneta americana (L.) (P.a.) and Periplaneta fuliginosa (Serville) (Dictyoptera: Blattidae) (P.f.) were tested. Behavioural choice tests between two resting sites demonstrated aggregation behaviour in the two species. Aggregation in both species is based on chemical cues. Periplaneta fuliginosa has a higher aggregation level than P.a. and responds only to its conspecific odour. Periplaneta americana is attracted by the odour of both species presented alone. In the presence of the odours of both species, P.f. selects its own odour, but P.a. neither selects its own odour, nor aggregates under these conditions. This could mean that the perceived chemical signals impair the aggregation process. In mixed groups including larvae of these two species, segregation between species occurs. We assumed that the first species that happened to form an aggregate on one of the resting sites induced the other species to occupy the remaining site. The emergence of a segregation pattern between the two species could be a consequence of the aggregation processes.