Could Species Segregation be a Consequence of Aggregation Processes? Example ofPeriplaneta americana(L.) andP. fuliginosa(Serville)

Abstract

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.

Analysis of emergent symmetry breaking in collective decision making

“…Aggregation behaviors of insects, as an example of simple natural swarm behavior, were frequently a subject of empirical research. Aggregation processes were investigated in several species, for example: bark beetles [6], ants [7,8], cockroaches [7,[9][10][11][12], and honeybees [13,14]. Some of these insects navigate by exploiting a gradient of odor [7], a gradient of population density [15], or by exploiting agent-agent encounters and a temperature gradient [14,16].…”

“…The focus in these works is on decision processes showing symmetry breaking with binary choices (left branch vs. right branch). Symmetry breaking with several but discrete choices (sources, shelters) was investigated in foraging honeybees [25] and cockroaches [9,10].…”

Intraspecific Signals Inducing Aggregation in Periplaneta americana (Insecta: Dictyoptera)

“…americana, two types of bioassays (binary choice tests and Y-olfactometer) were used. Binary choice tests in Petri dishes have been used previously in our laboratory to test aggregation abilities in cockroaches Cloarec 1998, Leoncini andRivault 2005) increased when methanol extracts were added. This means that at least some of the molecules that are present in each type of extracts are required to induce aggregation and that they act simultaneously, in complement or in synergy.…”

“…Among urban cockroach species, Periplaneta americana (L.) is gregarious and chemical communication is clearly involved in aggregation processes. Papers conditioned by conspecific odours are chosen as resting sites (Leoncini and Rivault 2005). Cuticular hydrocarbons play an important part in this message that enables aggregation on the odour source through tactile and/or volatile pathways (Saïd et al 2005a).…”

Ethology into a new era

“…Andersson 2005, Blanckenhorn 2005, Fieder et al. 2005, Handley & Nelson 2005, Leoncini & Rivault 2005), development (e.g. Amorim & Hawkins 2005, Brännäs et al.…”