It is now clear that whole genome duplications have occurred in all eukaryotic evolutionary lineages, and that the vast majority of flowering plants have experienced polyploidisation in their evolutionary history. However, study of genome size variation in microalgae lags behind that of higher plants and seaweeds. In this study, we have addressed the question whether microalgal phylogeny is associated with DNA content variation in order to evaluate the evolutionary significance of polyploidy in the model genus Micrasterias. We applied flow-cytometric techniques of DNA quantification to microalgae and mapped the estimated DNA content along the phylogenetic tree. Correlations between DNA content and cell morphometric parameters were also tested using geometric morphometrics. In total, DNA content was successfully determined for 34 strains of the genus Micrasterias. The estimated absolute 2C nuclear DNA amount ranged from 2.1 to 64.7 pg; intraspecific variation being 17.4-30.7 pg in M. truncata and 32.0-64.7 pg in M. rotata. There were significant differences between DNA contents of related species. We found strong correlation between the absolute nuclear DNA content and chromosome numbers and significant positive correlation between the DNA content and both cell size and number of terminal lobes. Moreover, the results showed the importance of cell/life cycle studies for interpretation of DNA content measurements in microalgae.
- MeSH
- biologická evoluce MeSH
- chromozomy rostlin genetika MeSH
- délka genomu genetika MeSH
- DNA rostlinná genetika MeSH
- fylogeneze MeSH
- genom rostlinný genetika MeSH
- Micrasterias genetika MeSH
- mikrořasy genetika MeSH
- Streptophyta genetika MeSH
- variabilita počtu kopií segmentů DNA genetika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Central European mountain bogs, among the most valuable and threatened of habitats, were exposed to intensive human impact during the 20th century. We reconstructed the subrecent water chemistry and water-table depths using diatom based transfer functions calibrated from modern sampling. Herbarium Sphagnum specimens collected during the period 1918-1998 were used as a source of historic diatom samples. We classified samples into hummocks and hollows according to the identity of dominant Sphagnum species, to reduce bias caused by uneven sampling of particular microhabitats. Our results provide clear evidence for bog pollution by grazing during the period 1918-1947 and by undocumented aerial liming in the early 90-ies. We advocate use of herbarized epibryon as a source of information on subrecent conditions in recently polluted mires.
Despite the significance of diatoms in biomonitoring, many aspects of their biodiversity and geographical distribution are poorly understood. Recent evidence from molecular data has shown that traditional cosmopolitan and euryvalent morphospecies are often heterogeneous, containing cryptic or pseudo-cryptic species. It is important to establish whether these more finely differentiated species are also cosmopolitan or show restricted distributions. According to the standard freshwater diatom floras, Navicula cryptocephala and morphologically similar species (N. veneta, N. trivialis, N. gregaria and N. cryptotenella) are common, cosmopolitan freshwater pennate diatoms. Although allopatric and even sympatric populations of N. cryptocephala are extremely similar morphologically, they have previously been found to be highly polymorphic with respect to reproductive and nuclear characteristics; however, molecular data supporting the existence of cryptic diversity were lacking. Phylogenetic analyses (LSU rDNA, ITS of the rRNA operon) of 52 strains of N. cryptocephala-like diatoms confirmed the existence of genetically distinct lineages within N. cryptocephala, and revealed a close relationship between N. trivialis and N. cryptocephala. Cytological, reproductive and morphological variation, investigated by means of landmark-based geometric morphometrics, were in congruence with molecular data. Two pseudo-cryptic species within N. cryptocephala coexist sympatrically and are widely distributed, occurring in both European and Australian lakes.
- MeSH
- biodiverzita MeSH
- DNA řas chemie genetika MeSH
- fylogeneze MeSH
- geny rRNA MeSH
- intergenová DNA chemie genetika MeSH
- konformace nukleové kyseliny MeSH
- mikroskopie MeSH
- molekulární modely MeSH
- molekulární sekvence - údaje MeSH
- polymorfismus genetický MeSH
- ribozomální DNA chemie genetika MeSH
- RNA řas genetika MeSH
- RNA ribozomální 18S genetika MeSH
- RNA ribozomální genetika MeSH
- rozsivky klasifikace cytologie genetika fyziologie MeSH
- sekvence nukleotidů MeSH
- sekvenční analýza DNA MeSH
- sekvenční homologie nukleových kyselin MeSH
- shluková analýza MeSH
- sladká voda mikrobiologie MeSH
- zeměpis MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Single (unpaired) vegetative cells of freshwater pennate diatom Neidium cf. ampliatum differentiated into gametangia and produced a single zygote (auxospore) via a pedogamic process. The gametic nuclei fused after auxospore expansion had begun. The auxospore expanded in parallel to the apical axis of the gametangium.
Suitable morphological characteristics for identification of zygnematalean algae were determined using a combination of classical light microscopy (LM) techniques, fluorescence microscopy (with blue and green excitation), scanning electron microscopy (SEM) and specialized culture methods. Characteristics of spore germination, growth and reproduction under culture conditions identified Zygnema chalybeo-spermum in a mixture of zygnematalean spores collected from a small fishpond in Czechia. Reproduction in general, particularly aplanospore formation and lateral conjugation was more frequent and occurred earlier in a nutrient poor medium than in a nutrient rich medium, where vegetative growth was more vigorous. Variability in spore size was wide and influenced by the origin (sexual and/or asexual) of the spores. Asexual spores, particularly partenospores were rounded and significantly smaller than sexual ones. Thus spore morphology alone (size and shape) is not a particularly helpful characteristic for species identification. The mesospore of mature spores contained lipids and a sporopolenin-like material (algaenan), which showed green autofluorescence with blue excitation. The mesospore ornamentation, the only characteristic found that is suitable for identification purposes, can be observed easily in LM and SEM after exospore removal by KOH treatment. Detailed LM and SEM observations of the zygospores of all Zygnema species thus could provide basic data necessary for the preparation of an atlas and key for species identification which, after completion with molecular methods, brings clarification into the genetic relationships between morphospecies.
- MeSH
- elektronová mikroskopie metody využití MeSH
- Eukaryota cytologie klasifikace růst a vývoj MeSH
- finanční podpora výzkumu jako téma MeSH
- fluorescenční mikroskopie metody využití MeSH
- mikroskopie metody využití MeSH
- rybářství MeSH
- spory cytologie izolace a purifikace klasifikace MeSH
- vodní hospodářství MeSH
