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 lcan initiate a sequence of interaction between two conspecifics.Gregarious behaviour in cockroaches is a famous example of presocial behaviourand it has been often studied from this point of view (Gautier, Deleporte & Rivault, 1988;Grandcolas, 1999; Nalepa & Bell, 1997; Schal, Gautier & Bell, 1984; van Baaren et al.,2002, 2003b). This behaviour has been recently analysed in a molecular and morphologicalcomparative framework in the subfamilies Zetoborinae and Blaberinae (Grandcolas, 1991,1993a, 1993b, 1998; Pellens, Legendre & Grandcolas, 2007; Pellens et al., 2007b) whichprovided both a phylogenetic reference and a natural history context for the interpretationof social behaviour observed in the laboratory (Grandcolas, 1991; van Baaren & Deleporte,2001; van Baaren et al., 2002; van Baaren et al., 2003a). In a first attempt to understandthe evolution of social behaviour, relevant categories such as “gregarious”, “solitary” and“subsocial”, have been mapped onto a phylogenetic tree based on morphology (Grandcolas,1993, 1998). Actually, ethological studies have documented that gregarious behaviours canbe different for some of their details (Grandcolas, 1991; van Baaren & Deleporte, 2001;van Baaren et al., 2002, 2003a) and that these details should be analysed and contrasted inevery species, not only considering broad behavioural categories. A small group of closelyrelated species has been already studied in detail and will be used here as an example ofhow the successive event-pairing method can be applied to behavioural sequences to infer aphylogenetic tree that is reasonably congruent with other data, and to propose hypotheses ofbehavioural evolution. We will not discuss the issues of behavioural plasticity which havebeen explored and controlled for in the specific papers about cockroach behaviour citedearlier.In the course of these behavioural studies, dyadic interactions in four species –namely Thanatophyllum akinetum Grandcolas 1991, Schultesia lampyridiformis Roth1973, Lanxoblatta emarginata Burmeister 1838 and Phortioeca nimbata Burmeister1838 – have been observed among 11 to 17 groups of six nymphs placed in standardconditions for each species, according to the protocol described in Grandcolas (1991)and van Baaren et al. (2002). Each group has been placed in an open-field arena. Theobservations began one hour later and lasted 15 min. The experimentations have beenrecorded on a Samsung Digital Camcorder VP-D11. The observations have been carriedout on nymphs in the mid of their development since this is the most characteristic andintense period of gregarious behaviour (Grandcolas, 1993b; van Baaren & Deleporte, 2001).One additional outgroup species Eublaberus distanti Kirby 1903 from the closely relatedsubfamily Blaberinae has been observed using the same procedures. Transition matriceshave been constructed using the behavioural sequences reported as described in the Figure1. As a matter of illustration, within a sequence B-A-C-D, the transitions B/A, A/C andC/D are observed and reported in the transition matrix. Phylogenetic analyses have beencarried out with these behavioural matrices, and also by comparison with a morphologicaland molecular data set. The morphological data are taken from Grandcolas (1993, 1998).284