Ecology, ontogeny, and morphometry of the freshwater centric diatom species complex, cyclotella bodanica/radiosa

Abstract

The genus Cyclotella is one of the most important components of the planktic diatom community in the majority of lakes in Canada, especially those on the Canadian Shield and in the Arctic. Many species of this genus exhibit a high degree of morphological variability. Populations of the Cyclotella bodanica/radiosa complex differ considerably from each other as well as from the described type species and varieties. This has placed their classification into a state of flux so that their use as indicator organisms in clim ology, paleoecology and/or paleoclimatology is limited. The major source of morphological variability could be related to size changes or allometry during ontogeny with a very weak relationship to a particular environmental condition. This study considered seasonality, ontogeny and allometry in several populations of the Cyclotella bodanica/radiosa complex: the seasonality was studied over several degrees of latitude ranging from temperate regions to the Arctic; size regeneration (via auxosporeproduction) was monitored under field and laboratory conditions; and changes in allometry were measured using a morphometric analysis of features used as "species distinguishing characters" including those from type material (actual or literature values). The majority of morphological variation could be attributed to allometric changes during ontogeny and no single character or any of the traditionally used taxonomic features separated the populations. The morphotypes described as species and varieties within the complex Cyclotella bodanica/radiosa must be considered synonyms as they can not be distinguished consistently and persistently from each other using ordinary means (in this case LM and SEM).