Delimitação de espécies e plasticidade fenotípica em microalgas verdes da família Selenastraceae: uma abordagem fisiológica

Abstract

Recently, discussions on conservation policies at different geopolitical levels have been widely debated. Species are the main indicators for estimating biodiversity parameters, playing a key role in biodiversity records. However, species delimitation is not an easy task. For some organisms, such as green microalgae that have a simple morphology and asexual reproduction, the species delimitation has been challenging. At first, taxonomy was based on morphological characteristics such as thallus organization and type of reproduction. However, for groups such as the family Selenastraceae, morphological characteristics are ambiguous at the genus level and do not reflect phylogenetic relationships. Other taxonomic approaches have been proposed for these complex groups, including the integrative approach, which considers morphological, molecular, ecological, physiological, and biochemical characteristics. In this context, we proposed the study on physiological changes (accessed by morphological and biochemical variations) to help differentiate 10 strains from the genera Kirchneriella, Selenastrum and Messastrum, which have cryptic species within the family Selenastraceae. Thus, we evaluated the algae response under different conditions such as variations in temperature, pH and nitrate concentrations. We have shown that physiological responses based on morphological results is not enough (or reliable) to delimit species. Cell size undergoes relevant changes in cell volume under environmental variations, in which it can increase or decrease up to 70% between different treatments; whereas as the temperature increases, the cell biovolume tends to decrease in all strains studied. Biochemical physiological responses were more efficient in the separation of taxa and reflected the phylogenetic data available in the literature. Therefore, physiological responses based on biochemical results have been shown to be an extremely useful taxonomic tool for species delimitation and can separate all genera and species, corresponding to molecular data.