Contribution à l’étude des relations entre individus chez cinq espèces d’iguanes malgaches du genre Oplurus

Abstract

The social behaviour of five species of Iguanid lizards from Madagascar Oplurus quadrimaculatus, O. grandidieri, O. fieri-nensis, O. cyclurus and O. cuvieri cuvieri is described. The field work was carried out near Tulear, Morondova and Soalala. The laboratory work took place, partly, at the Marine Station of Tulear and, mostly, in Marseille, where almost all the experiments were carried out. After summarizing relevant data on the ecology, morphology, and diet of these Iguanid lizards, the paper concentrates on the analysis of the relationships between individuals and their agonistic behaviour repertoire. The deterrent display and the threatening display, consisting of sequences of vertical oscillations of the front part of the body, are described. The study of 126 displays, using a frame by frame analysis of filmed sequences, shows the inter-specific variations. Some correlations between the morphology and habitat preferences of the various species and their display pattern are pointed out : the independent vertical movements of the head and neck are most often observed among the arboreal species (O. cyclurus and O. cuvieri), while the extension and rhythmic flexion of the fore limbs predominates among the more specialized rupicolous species (O. grandidieri and O. fierinensis). The aggresive displays which take place during short range confrontations contrast both O. fierinensis and O. grandidieri to the two arboreal species. Amongst the former, the threatening posture involves a dorso-ventral flattening, with a “ dorsal display ” to the adversary. Amongst O cyclurus and O. cuvieri, on the contrary, a lateral compression is apparent, and the animal presents to its opponent an enlarged profile. A special combat technique has been observed among O. grandidieri. Apart from these differences, many common display features draw the five species under consideration together, and confirm that this genus constitutes a fairly homogeneous taxonomic group. The territorial behaviour of Oplurus lizards is also conside¬ red. The five species have been subjected to a series of experiments in large terraria. With the exception of O. fierinensis, the male Oplurus demarcates an individual territory : two males of the same species cannot peacefully cohabit in a 10 m² area. The females are also intolerant of each other, but to a lesser degree : they are, on the other hand, accepted in the males’ territories. Territorial intolerance has also been observed under natural conditions amongst O. quadrimaculatus and cyclurus ; the area controlled by the male of the first species can exceed 100 m², but is smaller for O. cyclurus. A territorial male O. quadrimaculatus allows one or several females to settle at least temporarily on its territory. Some information is given on the mating display of O. quadrimaculatus and O. cyclurus. An analysis of the interspecific relations shows that Oplurus quadrimaculatus dominates the other species, except O. cuvieri. Interspecific confrontations are more frequent and more prolonged between species which are morphologically similar. The affinities and differences between Oplurus species as well as the relations between Malagasy and American Iguanids, are discussed. Some hypotheses on the origin of the ritual oscillations of the front part of the body among Iguanids and Agamids are put forward.