An ultrastructural and histochemical study of the secretory granules in the salivary gland cells of the Drosophila melanogaster species subgroup: phylogenetic relationships and evolutionary aspects

Abstract

The morphology of the secretory granules and the distribution of "neutral" complex carbohydrates in these structures of the larval salivary gland cells of six species belonging to the melanogaster subgroup of Drosophila were examined at the ultra-structural level. The secretory granules of each species show a unique morphology. The species of the melanogaster subgroup can be subdivided into two complexes (the melanogaster and the yakuba complexes) on the basis of the existence of filamentous or granular material in their secretory granules. In the former complex belong the species Drosophila melanogaster, Drosophila simulans, and Drosophila mauritiana, whose secretory granules consist mainly of filamentous material, and in the latter complex belong the species Drosophila yakuba, Drosophila teissieri, and Drosophila erecta, whose secretory granules consist of granular material. A phylogeny of the six species, in which D. erecta is regarded as the most primitive, is presented. It is proposed that the morphology of the secretory granules at the ultrastructural level, combined with the distribution of complex carbohydrates in them, can be used as an additional criterion for the classification of the Drosophila species.