Symmetric and Asymmetric Components of Shape Variation in the Diatom Genus Frustulia (Bacillariophyta)

Jana Kulichová,Pavla Urbánková

doi:10.3390/sym12101626

Abstract

Irregularities in cell division can produce asymmetry in symmetric structures, such as outlines of diatom cells, which can reflect genetic, environmental, or random variability in developmental processes. This study examined 12 phylogenetic lineages of the diatom genus Frustulia using landmark-based geometric morphometrics to assess the variation between cell segments separated by apical and transapical axes. Although asymmetric variation within cells differed in some lineages, these irregularities most likely did not reflect the evolutionary history of the lineages. The intraclonal phenotypic plasticity of diatom frustules was induced rather by nongenetic factors, i.e., inherited valve abnormalities, constraints of siliceous cell walls, and random developmental instability during morphogenesis. The positive correlations between the symmetric and asymmetric components of shape variation indicated that the morphogenesis of diatom cell walls affected irregularities within cells and variability among the symmetrized cells to a similar extent.

Highlights

Diatoms are eukaryotic microorganisms with bipartite siliceous cell walls that form shells resembling a Petri dish [1]
We examined 15 monoclonal strains representing 12 phylogenetic lineages of the genus Frustulia
The largest differences within strains were affected by symmetric differences between cells whereas asymmetric components of shape variation within cells were much less important (Table 1, Figure S1)

Summary

Introduction

Diatoms are eukaryotic microorganisms with bipartite siliceous cell walls that form shells (frustules) resembling a Petri dish [1]. The common occurrence of diatoms in heterogenous habitats and their morphological variability has led to the description of more than 8000 species [2]. Diatom classification relies principally on the overall shape, symmetry of the cell, and wall ornamentation. Similar shapes or symmetries may, undergo convergent and parallel evolution. Phylogenetic reconstructions [4,5,6], as well as ontogenetic studies [7,8,9], have been shown to be useful for the identification of homologies and for understanding the evolution of diatom morphology

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