Beschreibung
The Chew Bahir Drilling Project (CBDP) provides tropical sediment samples presumably spanning the last ~650 kyrs. DNA metabarcoding across these cores provides a paleolimnological record of a tropical lake environment, unique in both resolution and time span. In a pilot study, we could detect and analyze ancient eukaryotic DNA from the two parallel ~280 m long Chew Bahir cores in sediment layers down to 70 m, roughly corresponding to 150 kyrs BP. Our initial results indicate that methods first applied in arctic regions can be successfully employed also in a tropical setting. The key to this success is the application of Hybridization-capture-based metabarcoding. Here, sediment samples are (after total DNA extraction) subjected to taxon- and gene-specific DNA-enrichment via hybridization capture with specific probes (“baits”). Captured DNA is subsequently subjected to Next-Generation-Sequencing. For the following funding period, we aim at further evaluating the possibility for DNA metabarcoding in the long CBDP cores. The principal research questions addressed by the project are: (1) How far back in time can DNA remnants in the Chew Bahir and other HSPDP cores be extracted and analyzed? We will exploring the possibility for DNA-based detection of organisms in deeper layers of the cores (i.e., below 70m). Furthermore, we will optimize experimental conditions as to maximizing retrieval of DNA of our target taxa and to minimizing potential methodological biases. (2) What are the long-term trends and shifts in the organismal communities in the Chew Bahir and other African core records? – We will elucidate the temporal trend in the occurrence of target eukaryotes, both regarding species identity, cryptic genetic variation, and (semiquantitative) relative abundance. This will include planktonic organisms previously used as environmental proxies (ostracods, cladocerans, rotifers, diatoms), but further encompass key taxa of the terrestrial environment as well (insects, rodents, antelopes, hominids, higher plants). This representative taxon list will provide us with a comprehensive assessment of organismal communities and their dynamics through the time period covered by the cores. Our findings will be related to non-biological proxies on dating and environmental conditions in order to arrive at a comprehensive understanding of environmental change and organismal responses to this change. For a comprehensive assessment of Eastern African flora and fauna, we will maintain our established target barcoding genes and taxa, i.e., Cytochrome Oxidase I (COI) probes for metazoa and Rubisco Large Subunit (rbcL) probes for plants. We will utilize and further optimize the established hybridization capture protocol that had been successfully used in the first funding period. We specifically focus on the Chew Bahir core, but are open to include material from the other African HSPDP cores for comparison as well.