ABSTRACT
Cyanobacteria morphology has apparently remained almost unchanged for billions of years, exhibiting remarkable evolutionary stasis. Cyanobacteria appear to have reached their maximum morphological complexity in terms of size, modes of multicellularity, and cellular types by ~2 Ga. This contrasts with the increased complexity observed in other multicellular lineages, such as plants. Using experimental evolution, we show that morphological diversity can rapidly evolve in a species of filamentous cyanobacteria. Since size has such significance with regard to organismal complexity, we subjected the heterocyst-forming cyanobacterium Trichornus variabilis (syn. Anabaena variabilis) to selection for larger size. We observed increases in size of more than 30-fold, relative to the ancestral population, after 45 cycles of selection. Two distinguishable nascent morphological elaborations were identified in all the selected populations: Tangle (long, tangled filaments) and Cluster (clusters of short filaments) morphology. Growth from single cells indicates heritability of the evolved Tangle and Cluster morphological phenotypes. Cyanobacteria evolutionary conservatism is ascribed to developmental constraints, slow evolution rates, or ecological flexibility. These results open opportunities to study possibilities and constraints for the evolution of higher integrated biological levels of organization within this lineage.
Subject(s)
Anabaena variabilis , Anabaena , Anabaena/geneticsABSTRACT
Anthropogenic impacts increasingly drive ecological and evolutionary processes at many spatio-temporal scales, demanding greater capacity to predict and manage their consequences. This is particularly true for agro-ecosystems, which not only comprise a significant proportion of land use, but which also involve conflicting imperatives to expand or intensify production while simultaneously reducing environmental impacts. These imperatives reinforce the likelihood of further major changes in agriculture over the next 30-40 years. Key transformations include genetic technologies as well as changes in land use. The use of evolutionary principles is not new in agriculture (e.g. crop breeding, domestication of animals, management of selection for pest resistance), but given land-use trends and other transformative processes in production landscapes, ecological and evolutionary research in agro-ecosystems must consider such issues in a broader systems context. Here, we focus on biotic interactions involving pests and pathogens as exemplars of situations where integration of agronomic, ecological and evolutionary perspectives has practical value. Although their presence in agro-ecosystems may be new, many traits involved in these associations evolved in natural settings. We advocate the use of predictive frameworks based on evolutionary models as pre-emptive management tools and identify some specific research opportunities to facilitate this. We conclude with a brief discussion of multidisciplinary approaches in applied evolutionary problems.
ABSTRACT
Three types of hemoglobins exist in higher plants, symbiotic, non-symbiotic, and truncated hemoglobins. Symbiotic (class II) hemoglobins play a role in oxygen supply to intracellular nitrogen-fixing symbionts in legume root nodules, and in one case ( Parasponia Sp.), a non-symbiotic (class I) hemoglobin has been recruited for this function. Here we report the induction of a host gene, dgtrHB1, encoding a truncated hemoglobin in Frankia-induced nodules of the actinorhizal plant Datisca glomerata. Induction takes place specifically in cells infected by the microsymbiont, prior to the onset of bacterial nitrogen fixation. A bacterial gene (Frankia trHBO) encoding a truncated hemoglobin with O (2)-binding kinetics suitable for the facilitation of O (2) diffusion ( ) is also expressed in symbiosis. Nodule oximetry confirms the presence of a molecule that binds oxygen reversibly in D. glomerata nodules, but indicates a low overall hemoglobin concentration suggesting a local function. Frankia trHbO is likely to be responsible for this activity. The function of the D. glomerata truncated hemoglobin is unknown; a possible role in nitric oxide detoxification is suggested.
