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 lINTRODUCTION“Presocial” behavior, as defined by Wilson (1966, 1971) and Eickwort (1981), refers toassociations of conspecifics that show neither reproductive division of labor nor overlapbetween generations and therefore are not considered as “eusocial”. From an evolutionarypoint of view, such presocial behaviors are particularly interesting since they are supposed torepresent the possible first steps toward more complex and more integrated social behaviors.As a matter of example, gregarious and subsocial cockroaches are often assumed to representfirst steps in terms of social evolution toward the complex societies of the closely relatedtermites (Nalepa, 1994). However, the evolution of these gregarious and subsocial behaviorsthemselves is rarely studied and few is known about their specific origin. In this perspective,cockroaches offer rich opportunities of study since many species display diverse “presocial”behaviors such as gregarism or brood care. Laboratory studies and very few field observationsalready described active aggregation of larvae (hereafter named larval gregarism), of larvaeand adults (hereafter named mixed-group gregarism) and different kinds of brood care byfemales providing their larvae with either shelter or food, or both (Chopard, 1938; Rothand Willis, 1960; Schal et al., 1984; Gautier et al., 1988; Nalepa and Bell, 1997; Pellenset al., 2002, 2007a; Perry and Nalepa, 2003). Solitary behavior has also been observed incockroaches but few cases have been fully documented and their evolutionary significancehas been little discussed (Gautier et al., 1988; Grandcolas, 1997b, 1998b). The comparativestudy of this diversity should permit to better understand the evolution of the first steps ofsocial behavior, stressing the nature and the level of the differences among solitary, gregariousand subsocial species in terms of repertoire and social interactionsHowever, two problems limit our understanding of the evolution of social behaviorin cockroaches. First, the natural context of the observed behavior is generally unknown,because very few species have been studied in the field (Roth and Willis, 1960; Schal et al.,1984; Pellens et al., 2007a). Similarly, the behavior of domestic species lacks a natural context– strictly speaking out of human buildings – for understanding their evolutionary origin(Grandcolas, 1998a). Second, different kinds of social behavior are most often known for taxa316