Plasticidade morfológica em microalgas verdes cocoides em diferentes condições abióticas e suas implicações na delimitação específica

Abstract

The coccoid green algae have simple morphology, morphological convergence and phenotypic plasticity, characteristics that hinders their correct identification. Molecular data have been insufficient for specific delimitation, and since Selenastraceae are asexual, the biological concept of species is not applicable. Thus, recent studies propose an integrative taxonomic approach, uniting several species concepts (eg. morphological, phylogenetic, physiological) for a more natural classification. Morphological analysis, although very useful and widely used, must consider phenotypic plasticity in the face of environmental variations. In this study, we evaluated the morphological plasticity of seven strains of three morphological species of Ankistrodesmus, A. densus, A. fusiformis e A. stipitatus, submitted to different conditions of temperature (23±1°C and 30±1°C), pH (7,0 and 8,5) and nitrogen concentration (1000 and 200 µM nitrate). We use cell length, width and biovolume as morphometric parameters. The control treatment was cultivated at 23±1°C, pH 7,0 e 1000 µM nitrate. The strains responded differently to different treatments, with length being the parameter with the least variation. The increase in pH significantly increased the cell width (by up to 27%) of all A. fusiformis strains, reflecting an increase up to 53% in the biovolume, while reduced the cellular width of the A. densus strain by 6%. The increase in temperature reduced the cell width in three strains of A. fusiformis, but one of then responded similarly to A. densus, increasing its width and biovolume. On the other hand, the comparison between species showed that cell length was significantly greater in A. densus, even considering the entire abiotic variation. In this way, the environmental variations altered the range of morphometric values used to identify the species, but for the selected strains, despite the plasticity, the cell length differed the species.