Geometric morphometrics reveals increased symmetric shape variation and asymmetry related to lead exposure in the freshwater green alga Micrasterias compereana
Abstrakt
Lead (Pb) contamination of surface waters caused by its gradual release from soils has been reported in acidic wetlands located near industrial regions that experienced significant atmospheric Pb deposition during the 19th and 20th centuries. The green algae belonging to Desmidiales are typically one of the dominant components of the phytobenthos in these habitats, and experimental studies have shown that morphogenesis of desmid cells can be significantly affected by increased Pb concentrations in the environment.
This study focused on an analysis of the shape variation in cells of the model desmid species Micrasterias compereana exposed to low chronic levels of Pb contamination. The geometric morphometrics of biradial symmetry and asymmetry of cellular lobes detected a significant increase in the shape variation corresponding to the Pb exposure of populations.
However, the sensitivity of this relation was considerably different in the individual subspaces of the symmetric variation and asymmetry. The symmetric variation of the lateral lobes among the cells and the asymmetry between two opposite semicells were the most sensitive components to Pb exposure.
Conversely, the left-right asymmetry between two cellular halves across the vertical axis and the transversal asymmetry between the lateral lobes were considerably less sensitive. In addition, the bilateral fluctuating asymmetry in the shapes of two adjacent cellular lobules was also susceptible to increased Pb contamination.
Thus, the results showed that quantitative changes in the morphological variation of desmid populations evaluated by the biradial symmetry and asymmetry of cells might be used as sensitive biological indicators for the detection of Pb pollution in dystrophic freshwater habitats, such as peatbogs and acidic fens.