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 lDISCUSSIONThe subfamily Zetoborinae shows a high diversity of social behaviors, comprisingsubsociality (here P.b.), larval gregarism (L.e. and P.n.), mixed-group gregarism (S.l.), andsolitariness (T.a.). These behaviors are well-characterized in the field by population structuresand space utilizations in the different species (Roth, 1973; Grandcolas, 1991, 1993a; Pellenset al., 2002; van Baaren et al., 2002) but have never been compared in detailed laboratorystudies for all the species included in the present study.The present research showed that diversely gregarious species of Zetoborinae havea higher tolerance to crowding and to contact than the solitary T.a. Even if maintained athigh densities in cultures since their birth, individuals of T.a. usually avoid direct contactwith conspecifics. However, surprisingly, they do not space themselves according to theavailable area. It must be noted that the experimental device provides all of them with enoughdorsal contact to avoid any artificial and forced aggregation caused by thigmotactic stress.Aggregation can be explained in terms of interactions between individuals (Jeanson et al.,2005) and this lack of contact between individuals could result from idiosyncratic behaviorsfavoring spacing, and notably agonistic behaviors (King, 1973).However, the comparison between solitary, gregarious and subsocial species yieldedunexpected results in this respect. First, behavioral interactions are weakly contrasted amongspecies. The repertoires are not very different and only three acts are exclusive of two species.The solitary T.a. does not show a smaller repertoire, or significantly shorter interactions (interms of number of acts per sequence) than gregarious species. Actually, only the mixedgregarious species (S.l.), showed longer interaction sequences. So, the diversity of socialsystems in Zetoborinae is clearly not related to a major behavioral differentiation but hasprobably been built on a same ancestral repertoire with changes mainly in its use.Moreover, the frequencies of the different transitions during the behavioral sequencesare roughly similar as revealed by the correlation test among the five transition matrices. Forexample, there is no clear relationship between the social system and the general level ofagonistic behavior (Table IV). Agonistic behavior in Zetoborinae cannot be said to reduce324