Morphometric Asymmetry of Frustule Outlines in the Pennate Diatom Luticola poulickovae (Bacillariophyceae)

Abstract

Abstract:Side orientation of cells is usually ambiguous in unicellular organisms, making it impossible to separate components of directional asymmetry (DA) and fluctuating asymmetry (FA). However, frustules of the diatom Luticola poulickovae have biradially symmetric outlines, and their central areas bear ornamentation that is asymmetric across the apical axis. The goal of this study was to explore differentiation of morphometric asymmetry across the apical axis into DA and FA components. Is there detectable DA of the valve outlines of two L. poulickovae strains that may be related to the asymmetric central areas? Given that the life cycle of diatoms involves cell-size diminution, and cell shape is strongly affected by allometry, we also explored the question of whether asymmetry is correlated with cell size. The extent of symmetric variation among individuals in each strain, as well as DA and FA across the apical axis, were quantified using two Procrustes ANOVA models. The results revealed no correlation of either total asymmetry or FA with valve size. DA was significant and considerably more pronounced than FA in both strains, indicating that there is previously unknown systematic asymmetry of valve outlines of L. poulickovae, which may be related to the asymmetry of its central area.

Morphological allometry constrains symmetric shape variation, but not asymmetry, of Halimeda tuna (Bryopsidales, Ulvophyceae) segments

“…It should be noted that this feature is typical for most algae and protists, but it is very rare or even lacking in bilateral animals and vascular plants [ 15 ]. A number of different microalgae are characterized by complex symmetric arrangement of their cellular parts, such as the lobes of Desmidiales or Hydrodictyaceae [ 27 , 28 ] or frustules of pennate diatoms [ 29 , 30 ]. However, due to side ambiguity, symmetry analysis of these structures often cannot involve the separation of the individual components of asymmetry.…”

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

“…The changes in cymbelloid shape observed in Frustulia (Figure 4) are not consistent with the directional asymmetry of Luticola species, where the most pronounced changes were observed in the middle part of the valve outline [18,55]. A possible explanation for the increased cymbelloid asymmetry in the middle part of Luticola valves is in the form of an initial cell (the first frustule of maximum size developed from the auxospore) that, in some/all Luticola species, has a markedly swollen outline in the middle part [55,57]. Indeed, the final shape of a frustule is associated with the specific development of the auxospore [7].…”

“…We reduced the effect of ontogenetic shape changes by selecting strains that were both above their minimum size (fewer cell divisions after sexual reproduction) and exhibiting limited variability in size (Table S1). Insignificant correlations between asymmetric components and size-shape trajectories in several biradially symmetric strains of different genera indicate that at least the asymmetric variation is not profoundly influenced by ontogenetic changes [16,55]. Comparisons of strain pairs from three lineages indicated similar patterns in morphological (a)symmetry within lineages/species (Table 1, Figure 2).…”

“…Diatoms that are classified as bilaterally symmetric may also exhibit more or less visible cymbelloid symmetry. For instance, the genus Luticola exhibits cryptic [18,55] as well as apparent dorsiventrality (e.g., [61]), but also balanced levels of asymmetric shape components [16]. Cymbellales share with at least one Luticola species [57] the cis symmetry (i.e., the primary sides of both valves are on the same side [59]), whereas representatives of the genera Frustulia and Amphipleura (F. saxonica, F. vulgaris, A. pellucida; [59,62]) have both cis and trans symmetry (i.e., primary sides of the valves are on the same or on opposite sides of the frustule).…”

Shape outline extraction software (DiaOutline) for elliptic Fourier analysis application in morphometric studies

“…The groups could be a biological cluster of shape‐related taxa, represent the variable forms of phenotypic expression, or even reveal phylogenetic relationships. Woodard and Neustupa () used geometric morphometrics with valves from Luticola polickovae to demonstrate that total asymmetry and fluctuating asymmetry were stable within a strain, whereas changes in directional asymmetry were more evident. Even seasonal changes in unicellular shape can be studied (Steinman and Ladewski, ).…”