The development of larval behaviours in the mesophragmatica group of species of drosophila

The development of behaviours in larvae of six species of the mesophragmati ca group of Drosophila was investigated. The goals were: (i) to uncover pat terns of development and evolution of behaviours, and (ii) to establish beh avioural phenograms in order to compare them with the phylogenetic relation ships based on chromosomal and isoenzymatic marker studies. In the presence of food, feeding, locomotion, turning, rearing, retreat and bending were r ecorded. During the whole larval period (24-28 to 192-196 h of age) D. meso phragmatica and D. viracochi show clear, regular but contrasting patterns o f development for these behaviours. Fluctuations across larval age were obs erved for the behaviours exhibited by D. pavani, D. gaucha, D. gasici and D . brncici. As larval development progressed the behaviour of the six specie s became more differentiated. Larvae of the six species also differed in be havioural organization. The preadults of the species showed high recurrence of feeding and locomotion. In D. mesophragmatica, D. viracochi and D. gasi ci some elements of behaviour tended to occur in triplets of regular sequen ce, whereas sequences of two elements were observed in larvae of D. pavani and D. brncici. D. gaucha larvae do not show sequential dependency of behav ioural elements. Behavioural similarity among the six species tends to foll ow the phylogenetic relationships established by chromosomal and isoenzymat ic studies. The findings suggest that genetic differences among the six spe cies are expressed in the development of larval behaviours.