THE DEVELOPMENT OF LARVAL BEHAVIOURS IN THE MESOPHRAGMATICA GROUP OF SPECIES OF DROSOPHILA

The development of behaviours in larvae of six species of the mesnphragmatica group of Drosophila was investigated. The goals were: (i) to uncover patterns of development and evolution of behaviours, and (ii) to establish behavioural phenograms in order to compare them with the phylogenetic relationships based on chromosomal and isoenzymatic marker studies. In the presence of food, feeding, locomotion, turning, rearing, retreat and bending were recorded. During the whole larval period (24-28 to 192-196 h of age) D. mesophragmatica and D. viracochi show clear, regular but contrasting patterns of development for these behaviours. Fluctuations across larval age were observed for the behaviours exhibited by D. pavani, D. gaucha, D. gasici and D. brncici. As larval development progressed the behaviour of the six species became more differentiated. Larvae of the six species also differed in behavioural organization. The preadults of the species showed high recurrence of feeding and locomotion. In D. mesophragmatica, D. viracochi and D. gasici some elements of behaviour tended to occur in triplets of regular sequence, whereas sequences of two elements were observed in larvae of D. pavani and D. brncici. D. gaucha larvae do not show sequential dependency of behavioural elements. Behavioural similarity among the six species tends to follow the phylogenetic relationships established by chromosomal and isoenzymatic studies. The findings suggest that genetic differences among the six species are expressed in the development of larval behaviours.