| Karol Krak | PhD | "Molecular phylogeny and evolutionary trends in Hieracium (Asteraceae, Lactuceae)" |
Proposal: The genus Hieracium L. is one of the most species rich groups in the plant kingdom. The genus is well known for its taxonomic complexity caused by extensive past and present hybridization in association with variation in ploidy levels and breeding systems, which gave rise to a big variety of morphological forms.
Focusing on the subgenera Chionoracium and Hieracium s. str. to complement previous studies dealing with subgen. Pilosella, the principal aim of this work is to establish a molecular phylogeny of Hieracium. We will attempt to cover the entire genetic diversity at a coarse level as a prerequisite for further, more detailed studies. For this purpose sequencing of the chloroplast trnT-trnL intergenic spacer and nuclear ribosomal ITS region will be performed. According to the nowadays-existing trend to use single or low copy genes for phylogenetic analysis, there is an effort to establish such system also for Hieracium. As soon as it will be available, it shall be used in our study as a third marker. Overall genetic vs. morphological variability and results obtained from different genetic markers (cpDNA vs. nuclear DNA) will be compared. The role and impacts of different breeding systems on speciation events and the origin of polyploids shall be inferred. Relationships at infrageneric and infratribal level shall be elucidated; the validity of present sectional and generic classifications and of the existing contradictory species concepts shall be assessed. |
|
| Radka Rosenbaumová | PhD | "Residual sexuality and haploparthenogenesis as a factor influencing population genetic structure in agamic complex of Hieracium subgenus Pilosella" |
Proposal: Apomixis is defined as clonal reproduction through seeds. Offspring rise without contribution of meiosis and fusion of gametes and are genetically identical to the mother plant. No variation is produced by this way.
In the past this fact lead to the assumption that apomixis represents a "blind alley" of evolution and causes evolutionary death of particular taxonomic group. But in almost all apomictic plants apomixis coexists with some level of sexuality (residual sexuality). Gametes fusing during sexual reproduction can be reduced or unreduced and can come from individuals with different ploidy level and / or from individuals belonging to different species. Also haploparthenogenesis (parthenogenetic development of reduced gametes) can occur. Both processes (residual sexuality and haploparthenogenesis) can give rise to an enormous variability that is in its essence dissimilar from variability common in offspring of sexual plants.
Facultative apomixis (apomixis in conjunction with residual sexuality) leads to the formation of intricate agamic complexes. The main characteristics of these complexes is an enormous diversity of the particular forms they consist of. In order to shed some light on the evolutionary significance of such diversity, this is necessary to detect individual processes that are involved in the formation of this diversity. Young recently developing agamic complexes are advisable for such research. In my study, I use subgenus Pilosella (genus Hieracium) as an example of such agamic complex.
Main questions and aims of my study are:
1) In what way do residual sexuality and haploparthenogenesis contribute to the differentiation / diversification of the population? (Are they important sources of evolutionary variability in populations of apomictic plants?)
2) Does apomixis manifest itself in fixation and stabilisation of the arising hybrid genomes?
3) Does sexual reproduction act as an important integrating force in populations of apomictic plants? (Does it contribute to the exchange of genetic material among apomictic lineages?)
Materials:
In my study I use a model system consisting of a hexaploid apomictic accession of Hieracium bauhini and a tetraploid sexual accession of H. pilosella (parental accessions), their natural hybrids and their artificially generated hybrids.
Methods:
Reciprocal crossing experiments are carried out between parental accessions. The aim of these experiments is to quantify apomixis, residual sexuality and haploparthenogenesis in the model system and to obtain a sufficient number of artificial hybrids. Determination of ploidy level by flow cytometry enables us to discriminate particular progeny classes. The mating system of particular progeny classes is estimated by emasculation experiments. Experimental crossings between artificial hybrids are planned to evaluate the role of residual sexuality in this model system. It is also planned to compare artificial hybrids (with known origin) with natural hybrids of unknown origin. This comparison will enable us to detect processes that could contribute to the origin of natural hybrids. |
|
| Tomáš Urfus | PhD | "Evolutionary mechanisms and relationships among taxa of Hieracium subgen. Pilosella" |
| Proposal: Basic and intermediate species
are usually distinguished within subgenus Pilosella (Hill) Gray. While intermediate species are considered as hybridogenous in origin, the origin and relationships among basic ones is unresolved. (1) The first part of the project comprises phylogeographic study of basic
species in subgen. Pilosella according to chloroplast (cp)
haplotypes. Studies done till now indicate existence of two major cp-haplotypes
groups (Fehrer et al. in press, Fehrer et al. 2005), which may reflect possible
distribution pattern of studied basic species during glacial periods.
Representatives of all species, which are considered as basic ones will be
analysed through the PCR-RFLP of cp DNA. This analysis will test preliminary
results based on low amount of samples. (2) The second aim of the study
is to reveal the potential allopolyploid origin of basic Hieracium
pilosella species by tracing back the contribution of diploid taxa from section Pilosellinae
and other potential introgressants. By mean of chloroplast
haplotypes and nuclear ITS regions analysis will be determined parental taxa of
H. pilosella and by the way wil be studied rate of introgression of
other species of section Pilosellina and whole subgenus Pilosella. (3) The variation of cp-haplotypes and nuclear ITS
regions of H. pilosella will be compared with variation of diploid
relatives (members of section Pilosellinae) to test the possibility of
allopolyploid origin of H. pilosella. |
|
