Patterns of symmetric and asymmetric morphological variation in unicellular green microalgae of the genus Micrasterias (Desmidiales, Viridiplantae)

Morphological symmetry and asymmetry in three clonal populations of Micrasterias cells was decomposed using a new geometric morphometric method specifically developed for shape analysis of complex symmetric structures. Micrasterias cells are symmetric relative to two perpendicular axes of symmetry: a left–right axis and a juvenile–adult axis. Shape variation is decomposed into a component of symmetric variation and other components of asymmetry. Principal component analysis suggested that symmetric variation and juvenile–adult asymmetry were dominant in describing morphological differences among objects in all three datasets. The left– right asymmetric variation among adjacent quadrants of the same semicells was consistently more pronounced than the asymmetric variation with respect to the transversal axis. The strains of Micrasterias radians var. bogoriensis (SVCK 389) and M. radians var. evoluta (SVCK 518) were consistently more variable than the population of M. semiradiata (CAUP K606), with respect to both symmetric and different aspects of asymmetric variation. The shape differences among cell quadrants from opposite semicells were statistically not different from shape differences among cell quadrants from different cells of clonal populations.