Experimental evolution in the cyanobacterium Trichormus variabilis: increases in size and morphological diversity

Beatriz Baselga-Cervera, Kristin A Jacobsen, R Ford Denison, Michael Travisano

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)1216-1225
Number of pages10
JournalEvolution; international journal of organic evolution
Issue number5
Early online dateFeb 23 2023
StatePublished - Apr 27 2023

Bibliographical note

Publisher Copyright:
© The Author(s) 2023. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE).


  • complexity
  • evolutionary stasis
  • experimental evolution
  • filamentous cyanobacteria
  • morphological diversity

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't


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