Evolution of morphological variability and modularity in single cells of algal colonies: A case study Pseudopediastrum (Hydrodictyaceae, Sphaeropleales, Chlorophyceae)

ABSTRACT

The present study is the first to investigate the evolution of morphological variability and modularity of single (marginal) cells in two-dimensional colonial (coenobial) microscopic algae. Geometric morphometric methods were applied to eight monoclonal strains forming a common phylogenetic lineage, composed primarily of Pseudopediastrum boryanum varieties. Both cell parts, the cell body and projections, exhibited great morphological variability, which was impacted more or less by allometry in six strains. A relationship between phylogeny and morphology was not found. Asymmetry was concentrated in the projections. The pressure of neighbouring cells in a coenobium might have stabilised the symmetry of the cell body and prevented its asymmetric fluctuations. Both cell parts were separate modules, but a strain with distinct perforations in coenobia, resulting in less contact with the neighbouring cells, exhibited stronger cell integration, generally regarded as a possible constraint for evolutionary changes. This suggested that the pressure of neighbouring cells can also act as a factor favouring cell modularity and, thus, the morphological evolution of the marginal cells.

KEYWORDS:

• Allometry
• Asymmetry
• Coenobium
• Geometric morphometrics
• Green algae
• Marginal cell shape
• Phylogeny
• Pseudopediastrum boryanum

ACKNOWLEDGEMENTS

The author is grateful to the anonymous reviewers for valuable remarks on the article.

Additional information

Funding

This work was supported by the statutory fund of the W. Szafer Institute of Botany of the Polish Academy of Sciences, including an in-house grant for young scientists in 2015.