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

An n e x e sbelonging to distantly related families (Grandcolas, 1998b). This loose taxon sampling istherefore not adequate to study the evolution of social behavior (but see Maekawa et al.,2003, 2005 and van Baaren et al., 2002 for recent advances in this respect).To provide new and adequate data, field and laboratory studies have been conductedon a diverse group of Neotropical cockroaches, the subfamily Zetoborinae (Grandcolas,1991), belonging to the ovoviviparous family Blaberidae (McKittrick, 1964; Roth, 1970;Grandcolas, 1996). Different subsocial, gregarious and solitary behaviors are known withinthe Zetoborinae. For example, young larvae of Thanatophyllum akinetum disperse early, oneday after brood birth. They are not found to aggregate again, even when they become adultsand shelter in patchy habitats in the understory (like litter piles at the basis of litter-trappingpalms, Grandcolas, 1993a). These features clearly characterize solitariness and they suggestthe occurrence of persistent spacing in this species. Conversely, the larvae of Lanxoblattaemarginata, like those of Phortioeca nimbata, shelter together beneath the fragments of loosebark on trunks. Because the number of larvae beneath each fragment is not related to fragmentsize or quality, it can be assumed that the aggregation of larvae is not a by-product of thehigh habitat patchiness but a real tendency to gregarism (Grandcolas, 1993a). Finally, recentstudies have shown that Parasphaeria boleiriana is not only gregarious in dead trunks butalso subsocial with the female and its nymphs remaining together in a wood chamber (Pellenset al., 2002). According to phylogeny (Fig. 1), gregarious behavior appears as the ancestralway of life in Zetoborinae, which changed to solitariness in Thanatophyllum akinetumand to subsociality in Parasphaeria boleiriana (Grandcolas, 1998b; Pellens et al., 2007a,2007b). Such contrasted ways of life could be supposed to result in deep behavioral changes.Nevertheless, this assumption has not been tested in the laboratory for the appropriate instars(those which are aggregated or not in the field) but for adults and first instar nymphs until now(van Baaren et al., 2002, 2003). Do solitary larvae have more simple behavioral repertoires?Do they display specific sequences interactions which promote more spacing than gregariouslarvae? Or, conversely, do gregarious larvae display richer repertoires and interactions(Wilson, 1971; Costa, 1997), are they more tolerant to or actually require crowding, whichare the basic characteristics of social way of life (Allee, 1931; Grassé, 1952; Eickwort,317