Evolutionary history of the genus Mallomonas (Chrysophyceae)

• Thesis title in Czech: Evoluční historie rodu Mallomonas (Chrysophyceae)
• Thesis title in English: Evolutionary history of the genus Mallomonas (Chrysophyceae)
• Academic year of topic announcement: 2022/2023
• Thesis type: dissertation
• Thesis language: angličtina
• Department: Department of Botany (31-120)
• Supervisor: doc. Mgr. Pavel Škaloud, Ph.D.
• Author: hidden - assigned by the advisor
• Date of registration: 06.10.2022
• Date of assignment: 06.10.2022

Preliminary scope of work

Background
The silica scales of Mallomonas species are provided by morphological structures obviously differing by their evolutionary dynamics. For example, the dome and the V-rib elements in the genus Mallomonas are extremely conservative structures with only rare cases of their evolutionary loss. This is most likely due to structural and developmental constraints, such as bristle attachment and their key role in organizing scales into a compact silica case, for the dome and the V-rib, respectively (Siver 1991). On the other hand, several elements, including various Turing patterns, are evolutionarily highly dynamic, evolving multiple times during the diversification of the genus (Čertnerová et al. 2019). Such traits are likely to be correlated with past climatic changes or may represent much recent ecological adaptations to the distinctive habitats. Multigene molecular clock analyses suggest that important diversification events in Synurales correlate with the intervals of elevated atmospheric CO₂ (Wolfe & Siver 2013). It is likely that such climatic shift may influence the development of morphological traits, as well.
Main questions
The main objective of this task is to search for possible correlation between the development of decorative elements and past climatic/ecological shifts or diversification events. By analysing organellar genomes, I will also get the most precise insight into the evolution and inner division of the genus Mallomonas.
1) How the taxa relationships based on genetic data corroborates the current taxonomy?
2) Is the development of decorative elements correlated with past climatic changes?
3) How the genus diversification correlate with geographic occurrence of particular Mallomonas species?
4) Did the development of specific decorative elements increase/decrease diversification rates?

Methodology
- Sampling: Particular Mallomonas strains will be isolated from a wide range of localities, including diverse ecological habitats and geographical areas. I will also employ the growing collection of strains already available in the lab of my supervisor.
- Genetic characterization of isolates, genus evolution: Chloroplast and mitochonsrial genomes will be obtained from every species to obtain a robust phylogeny of the genus.
- Morphological characterization of silica scales: The scales will be characterized using the TEM microscope. Several morphological traits (incl. scale dimensions, secondary structures patterns, etc.) will be analysed.
- Correlation of morphological traits evolution with past climatic changes: Climatic data tested will include cosmic ray flux, temperature, and atmospheric CO₂ concentration.
- Estimating diversification rates: We will estimate diversification rates of particular Mallomonas inner lineages, specifying the completeness of taxon sampling based on metabarcoding results.
- Geographic data: Occurrences of particular data will be retrieved from online databases (chrysophytes.eu, The Center for Research on Scaled Chrysophytes), as well as on published records.