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

An n e x e sanother species would answer by reciprocal aggression. Ethologists have known for a longtime that this kind of difference can be species-specific or common to related species. Sucha methodology allows more accurate assumptions of homology than when acts are taken inisolation. The occurrence of transitions between two particular acts can be treated as presenceabsencecharacters. The frequencies of transitions can also be used in addition since it is verydifferent to observe that a given transition is very rare or very common. Either a low or ahigh frequency can be considered characteristic of species and therefore used in phylogeneticanalysis as characters. Frequencies can be discretized and coded in different character statesusing gap coding (Archie, 1985; Stevens, 1991). Recently, Goloboff, Mattoni & SebastiánQuinteros (2006) argued that continuous characters need not to be discretized. However, theirmethodology treats continuous characters as additive characters, which requires an additionalset of assumptions that we do not want to follow here. Quantitative characters have proved tobe difficult to study in phylogenetic analyses, and the present work is not aimed at comparingand contrasting these methods. Therefore, we will focus this work on the most commonlyused approaches: discretization and gap coding.Our method requires that all these behavioural patterns, both the acts and the trends ofsuccession among acts, are largely heritable and that their plasticity and variability are low.This is the most basic and necessary assumption made by phylogenetic studies of behaviour,considering either stereotyped or non-stereotyped sequences. This assumption should besubstantiated in some way to legitimate a phylogenetic approach, as for other phenotypictraits (morphology, cytology, etc.). It can be partly done in evaluating the congruence of thephylogenetic tree based on behavioural data with molecular and morphological data. Otherbasic assumptions in phylogenetics deal with the minimal sampling effort needed to documentcorrectly the behaviours and with the independence of characters. Obviously, sampling effortand reasonable character independence should be, and will be, evaluated and discussedcritically before any comparative study to ensure an unbiased sampling of transitions andfrequencies in different species. These assumptions are not different than for other phenotypiccharacters, as already argued by Wenzel (1992).MATERIALS AND METHODSAn i l l u s t r at i v e c a s e s t u d y: g r e g a r i o u s b e h av i o u r in Ze t o b o r i n a e c o c k r o a c h e sNon-stereotyped behavioural sequences are most often observed in the context of socialrelationships. In this case, the observed behavioural sequence is not a series of actssuccessively emitted by the same individual, a situation which could occur with other kindsof behaviour such as territorial displays, grooming activities, etc., but a series of acts emittedby two individuals in alternation. These behavioural relationships are rarely stereotyped and,depending on the time and the context, the acts emitted by different individuals can differ.There is not a single answer to a particular act from a conspecific, and several different acts283