The frustule architecture of diatoms and the nature of the vegetative cell division phase of their life cycle constrain cell size and shape. For decades, diatomists have observed that size diminution is accompanied by valve shape changes. However, allometric shape changes have rarely been assessed using quantitative statistical tools. In the present study, we employed geometric morphometrics to examine the shape dynamics of raphid diatom frustules. An investigation was carried out to explore whether shape characteristics, such as circularity or asymmetry, and variation of valve outline, increase with decreasing cell size. Four monoclonal strains (Luticola dismutica strain 1, L. dismutica strain 2, Navicula cryptocephala, and Sellaphora pupula) were cultivated under stable conditions for two years in order to capture the complete range of cell sizes from initial to sexually competent cells. Shape changes and the pattern of shape change relative to size were quantified using geometric morphometrics. A quantitative shape analysis revealed similar allometric trends among the different strains and genera. With decreasing cell size, circularity of the valve outlines increased, that is, the complexity of the valves decreased. However, shape variation of valves within the populations increased with decreasing cell size. The levels of asymmetry did not change consistently throughout the size diminution phase. In two out of four strains, horizontal (dorsiventral) asymmetry was significantly lower than vertical (heteropolar) and transversal (sigmoid) asymmetries. The increasing morphological variation in clonal strains was likely caused by an accumulation of structural deviations during morphogenesis. In this respect, this is a specific example of the structural inheritance of morphological characteristics, which is naturally related to the peculiar vegetative life cycle of the diatoms.

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.

Ombrogenous peat bogs at lower altitudes of the Bohemian Massif occur close to their natural climatic limits in the Northern Hemisphere. They have been significantly affected by peat extraction and severe acidification. Recently, climate change effects, such as decreased snow cover and summer heat waves, have resulted in frequent seasonal desiccation of these habitats, indicating their ongoing transition into a different ecological state. Biomonitoring may provide insight into these rapidly changing ecosystems and identify key habitats for biodiversity conservation. The present study focused on the community structure of desmids, one of the most frequent groups of peatland phytobenthos. In total, 207 sites were sampled from the Ore Mts. (Czech Republic) at the altitude range of 750–850 m a.s.l. A modification of the desmid-based nature conservation value (NCV) index was devised to account for the differences among the observed strongly acidic habitats. In the fragments of ombrogenous bogs, which currently cover less than 3% of the area, several ecologically sensitive taxa, such as Cosmarium sphagnicolum and Staurastrum scabrum, were recorded. These taxa did not occur in other habitat types. In addition, the NCV indices of the bog samples were consistently higher than those of the restored pools created in the disturbed bog areas. However, the highest species richness was recorded in several slightly acidic ponds and sinkholes, which were often located outside the existing protected areas. Thus, we concluded that future conservation strategies should consider the remaining bogs and anthropogenic sites as habitats with relatively high ecological values.

Desmids are usually abundant in shallow peatland pools. In these localities, water temperature is closely linked to seasonal fluctuations in air temperature, so with increasing temperature extremes in temperate ecosystems, these microalgae are exposed to conditions of high-temperature stress. We investigated whether the shape, size, and growth rates of Micrasterias thomasiana, a frequently occurring species, are associated with varying temperatures in cultures and natural populations. The research was based on parallel analysis of clonal populations in temperature levels from 13 to 33 °C as well as cells from natural populations collected during the season. The effects of high temperature on morphological plasticity and fluctuating asymmetry in the shape of cellular parts were investigated by the landmark-based geometric morphometrics. The results showed that variation among individuals and fluctuating asymmetry between the lateral lobes of Micrasterias cells increased at 29 °C and in natural samples taken in July and October. In parallel, the size of semicells growing at temperatures above 25 °C decreased compared to those grown at lower temperatures. However, the temperature effects on shape and size were not directly related to the growth rates. The overall bilateral asymmetry between semicell halves did not change in relation to varying temperatures. In general, the results showed that morphological variation in natural populations of M. thomasiana reflected seasonal cycles and corresponded to plasticity associated with temperature changes in clonal cultures. It might therefore be possible to use these phenotypic markers as indicators of thermal stress in natural populations inhabiting shallow pools in peatlands.