PHENOTYPIC VARIATION OF LIFE-CYCLE STAGES IN CLONES OF THREE SIMILAR CYCLOTELLA SPECIES AFTER INDUCED AUXOSPORE PRODUCTION

Abstract

Auxospore production was induced in clonal cultures of three morphologically similar Cyclotella species, C. meneghiniana, C. gamma and C. quillensis to determine the pattern of variation of the frustule morphology through the life-cycle. Investigations were made by light and electron microscopy. The Cyclotella species have in common the tangential undulation of the smooth central area, striated marginal area, presence of valve face and mantle fultoportulae with three satellite pores and at least one rimoportula. Each of the three species produced two size groups with slightly different valve morphology. The morphological characters of the two size groups can cause identification difficulties, especially when found together. This paper presents an interspecific comparison of the morphology of the siliceous cell wall of the initial cells and their descendants. Auxospore production was induced in a small portion of the cells 3–12 days after transfer into seawater based saline medium (7.5 %). The initial cells showed species-specific structures and have taxonomic potential in delimitation of the Cyclotella taxa. Initial cell valves were hemispherical or domed, but cells with a relatively flat central area were found, complicating identification. The complex morphology of initial cells found in this investigation has shown that C. wulfiae is the initial cell of C. meneghiniana.