Currently we attempt to solve three problems in evolutionary history of ciliates:
- Phylogenetic interrelationships among free-living, predatory litostomatean ciliates
- Diversity and evolution of hindgut ciliates from wood-feeding cockroaches and their associations with prokaryotes
- Evolution of the ciliate/invertebrate symbiotic systems
1. Phylogenetic interrelationships among free-living litostomatean ciliates
The class Litostomatea represents a monophyletic group, comprising both predatory and endosymbiotic ciliates distributed all over the globe. At first glance, litostomateans are rather simple, uniformly ciliated protists having bursiform bodies. Their oral structures are very diverse, a fact that was used in their morphology-based taxonomy during the ultrastructure era. In the recent decades, the systematic research on litostomateans has concentrated mainly on the ribosomal RNA genes and ITS-region sequences. Phylogenetic relationships among main free-living litostomatean lineages are still unresolved, however. We search for evolutionary forces and investigate problems that might be associated with the puzzling picture in litostomatean phylogenies. We also examine the utility and phylogenetic information content of ribosomal and protein-coding genes in free-living litostomateans.
2. Diversity and evolution of hindgut ciliates from wood-feeding cockroaches and their associations with prokaryotes
The ability to digest wood evolved two times independently in the insect order Blattodea. First, in the common ancestor of termites and cryptocercids, and then in the panesthiine cockroaches. The hindgut compartment of panesthiines harbors a diverse, anaerobic microbial community, including also three closely related ciliate genera Clevelandella, Paraclevelandia, and Nyctotherus. These ciliates are, however, not associated with the digestion of wood but contribute to the overall hindgut function by their grazing behavior, which helps to shape and regulate prokaryotic populations. We investigate co-occurrence and correlation patterns of prokaryotes associated with these hindgut ciliates. We also study speciation, species borders, and mechanisms that have led to diversification of the hindgut ciliates.
3. Evolution of the ciliate/invertebrate symbiotic systems
Many animals have established associations with some epi- and/or endozoic ciliates. The free-living flatworms and terrestrial annelids do not represent an exception. However, the diversity of these symbiotic systems is far from being thoroughly examined. Present phylogenetic studies suggest that divergences of endosymbiotic ciliates are related to those of higher taxa of their hosts. Our main goal is to address the following questions:
- How many times have ciliates entered into associations with freshwater tricladid flatworms and terrestrial oligochaetes?
- Are various groups of endosymbiotic ciliates more closely related to free-living or to other symbiotic ciliates?
- Does the position of symbiotic ciliates in phylogenetic trees copy occurrence of their hosts in the geological history of Earth?