Phylogénie Et Evolution Du Comportement Social Chez Les Blattes ...

Ev o l u t i o n d u c o m p o r t e m e n t s o c i a lresponders revealed that interactions in P.b. are not symmetrical, contrary to interactions inthe four other species. Except few behavioral acts like “approach” or “kick”, acts are ratherspecific to the initiator of the interaction or the responder in P.b.: thus, initiators displayedmuch more dominance-like behaviors (“climb”) whereas responders displayed moreavoiding behaviors (“body leaning”, “crouch” or “move back”). A cause or a consequenceof subsociality could be the establishment of a dominance hierarchy within the population.Such hierarchy would explain the agonistic acts observed in P.b. (“kick” and “butt”) andthe asymmetrical interactions (Bell et al., 1979; Gautier and Forasté, 1982). However, thishypothesis needs to be tested in future analyses, especially with respect to another possiblecause: the evolution toward living in wood galleries where individual interactions are stronglyconstrained and possibly reduced by the immediate environment.Because T.a. is the only known solitary species which can be compared to gregariousspecies in the subfamily Zetoborinae, the generalization of these results is difficult and shouldbe achieved in the future when comparing solitary and gregarious species from the relatedsubfamilies Blaberinae, Gyninae and Diplopterinae (Grandcolas, 1993b, 1997c, 1998b;Pellens et al., 2007a, 2007b; in prep.). The morphological phylogeny of this group, recentlycorroborated by molecular studies, indicates that solitariness evolved as a reversal from anancestral gregarism, while the ancestral habitat (ground litter) was conserved only in thesolitary species (Grandcolas, 1997b, 1998b; Pellens et al., 2007a, 2007b). Does this reversedcondition in the behavior of T.a. explain the weak behavioral differences with gregariousspecies? Additional studies are needed to substantiate such a hypothesis of phylogeneticinertia. Ancestral solitariness should be documented in another clade and compared withsolitariness issued from an evolutionary reversal. But ancestral solitariness could be rare incockroaches because of egg clustering in oothecae and subsequent larval aggregation at broodbirth which may have favored evolution toward gregarism (Grandcolas, 1996).A final question concerns the role of communication in gregarious cockroach larvae:what kind of information is transmitted between the members of groups? This informationmay be relevant for group recognition, helping cockroaches to maintain stable aggregations(Wileyto et al., 1984; Rivault and Cloarec, 1998; Ame et al., 2004). It may also be used in326