On 27 August at 14:15 Liisi Talas will defend her doctoral thesis “Reconstructing paleo-diversity, dynamics and response of eukaryotes to environmental change over the Late-Glacial and Holocene period in lake Lielais Svētiņu using sedaDNA”.
Associate Professor Veljo Kisand, University of Tartu
Senior Researcher (Researcher II) Jessica Louise Ray, Norwegian Research Centre AS (Norway)
Biological material carried into the lake or originating from the lake accumulates over time into lake sediments where the extracellular DNA can bind to clay minerals and humic acids and thus preserve over long periods of time. The oldest known DNA detected from lake sediments dates back to ~270 000 years. Sedimentary ancient DNA (sedaDNA) allows us to reconstruct past biodiversity changes and enables us to identify when and why these changes in diversity appeared. In addition, sedaDNA permits us to study the impact of environmental change on these communities over the long timescale. The studies of relationships between community dynamics and environmental drivers are necessary to understand biodiversity changes and to model possible future scenarios during ongoing climate warming conditions. SedaDNA is a relatively new tool in paleoenvironmental research, where the use of sedaDNA has increased rapidly in the last five years due to the development of DNA sequencing and data analysis methods.
This thesis focuses on studying the effectiveness of sedaDNA reconstructing the changes in eukaryotes diversity, focusing on phototroph and fungal dynamics, and exploring the community responses to the environmental changes in the lake Lielais Svētiņu. Lielais Svētiņu can be considered a natural model lake in the North-East Europe region since it has a long sediment record, relatively late human impact in the region and availability of detailed dataset from previous pollen, micro-, and macrofossils studies. This data enables us to study natural and anthropogenic influences on the communities in lake ecosystems and wider changes in the area. As an innovative approach, the fungal ecophysiological groups were tested as new signatures of ecosystem changes in the lake and its surroundings. Firstly, it was found that sedaDNA can be successfully used to assess the biodiversity of eukaryotes also from deeper sediment layers. Also, sedaDNA enables the reconstruction of aquatic ecosystems and terrestrial environments of the lake catchment. In addition, the fungal ecophysiological groups recovered by the ITS2 marker region were found useful as signatures of past host populations and in-lake processes. Also, detected changes in community dynamics of eukaryotes were influenced by natural and anthropogenic factors. Three perturbation periods for phototroph dynamics were detected, of which two – Late-Glacial (~12 500-7700 kyr) and Holocene thermal maximum (~5400-7700 kyr) periods – were likely induced by abrupt climate change or by the effect of ice-cover and humification processes, respectively. The clearest richness change was observed in the last ~2000 kyr when richness rise occurred in Chlorophyta, plankton parasitic fungi and mycorrhizal fungi. These changes were related to the growing anthropogenic impact in the region. Such change in community dynamics can be explained by the higher loading of nutrients in the lake due to human activity. Higher amounts of nutrients, in turn, favored the richness increase in phytoplankton. In addition, the richness rise of plankton parasitic fungi started from ~4000 kyr, which could be explained by climate cooling and cyanobacteria-eukaryotic algae shift.