Assessing patterns of morphological and physiological trait variations across heterocytous cyanobacteria at cellular and population levels

Abstract

Heterocytous Cyanobacteria show high trait variation at the cellular, organismal, and population levels. Members of this group can produce specialized cells such as akinetes and heterocytes that influence their ecology, including bloom development and population survival. This study characterizes patterns of variation in the traits of these species, including the traits of specialized cells, to expand our ecological knowledge and predictive capacity for this group. We compiled and synthesized morphological and physiological traits of planktic heterocytous Cyanobacteria from the published literature and experiments, and assessed trait distributions, trait relationships, and their similarities among species. Although the volumes of akinetes and heterocytes were positively related to that of vegetative cells, the shape of cells differed in ways that may reflect their function, and the position of heterocytes within filaments may relate to growth rate. Maximum growth rates differed significantly among genera, yet surprisingly did not correlate with cell volume. Also, despite the high energetic cost of N fixation in low N conditions, our results suggest that growth rate seems unrelated to nitrogen availability. The degree of trait variation within heterocytous Cyanobacteria, which suggests the existence of three functionally distinct subgroups, may offer new insights into which taxa dominate bloom assemblages under different conditions.