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Organic geochemical study on the life history of lichen and fungi: Search for the molecular fossils and the reconstruction of fungal flora evolution
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| Title: | Organic geochemical study on the life history of lichen and fungi: Search for the molecular fossils and the reconstruction of fungal flora evolution |
| Other Titles: | 地衣類・菌類の有機地球化学的手法による地球生命史研究：分子化石の探索と菌類フロラの変遷史復元 |
| Authors: | 池田, 雅志 Browse this author |
| Issue Date: | 23-Mar-2023 |
| Publisher: | Hokkaido University |
| Abstract: | Lichens are organisms that have adapted to extreme environments by forming symbioses between fungi and algae, and are known as typical pioneer plants that expand into bare ground at the beginning of plant succession. The appearance of lichens is ancient, and fossil records indicate that they were already present in the early Devonian (Taylor et al., 1995a,b; Honegger et al., 2013a,b). Recently, molecular phylogenetic analyses have reported that many lichens diversified with environmental changes during the Cretaceous; Gaya et al. (2015) used molecular phylogenetic analyses to report that the pigment phenotype of the lichen family Teloschistaceae changed during the Mid-Cretaceous, which may have resulted in strong UV tolerance, expansion and diversification into bare ground. On the other hand, the fossil record itself is rare in its production due to factors such as habitats that are difficult to preserve and biases such as the observation of microstructures necessary for identification and separation from sedimentary rocks. Therefore, paleoecological studies of lichens at the earth-history level have been limited to studies using extant lichens. Therefore, the objectives of this study were to search for lichen biomarkers, develop lichen vegetation indices and reconstruct paleoecology. As a first step, lipid analysis of extant lichens was performed to examine indicator organic molecules. As a result, we found that the lichens contained aliphatic hydrocarbons, including n-alkanes, alkenes, and long-chain branched alkanes, fernenes, diploptene, and hop-21-ene. Lichens with a green algae photobiont (photosynthetic symbiotic algae) contained 1,8-heptadecadiene or 6,9-heptadecadiene and 8- and 7-heptadecene, whereas lichens with cyanobacteria as a photobiont did not contain the heptadecadienes but did contain octadecene, nonadecene and nonadecadiene. These differences in characteristics could be attributed to phylogenetic differences in the photobionts that comprised the lichens, indicating that the alkene composition could be used for lichen chemotaxonomy. These results suggest a previously unknown origin for the C17–C19 alkenes in sediments and implied that these components could be used to reconstruct the past composition of lichens. As a next step, we focused on lichen secondary metabolites, known as lichenspecific components. Among oxygen-containing aromatic compounds, dibenzofurans has been reported as a universal compound in lichens, and lichens are known to be the main producers in nature. Since lichens in nature have a methyl group specifically in the first position of methyl dibenzofuran, this study examined 1-methyl dibenzofuran as a lichen biomarker and indicator. As a results for, The 1-MDBF index showed no abrupt changes at both sites. The ratios of aromatic terpenoids to perylene and higher plant origin terpenoids indicated a relative increase during the decay period of fungi and higher plants. The cold weather event is known to occur in the North American samples during the through-phase, suggesting that lichens of 1-MDBF origin are highly tolerant to environmental changes and are not affected by environmental fluctuations. Based on the findings obtained, we also evaluated the usefulness of oxygen-containing aromatic compounds as lichen tracers. Several aromatic furans were detected in the Mesoproterozoic (1.2-1.0 Ga) sedimentary rocks of the Qaanaaq Fm. in northwestern Greenland. The isomer ratios and abundances of the aromatic furans detected varied from stratigraphic level to stratigraphic level. This may be attributed to changes in the contribution of the source material at the time of deposition, rather than to the effect of maturity. Aromatic furans are suggested to be possible terrestrial sources, and these compounds in the Mesoproterozoic may be important evidence in discussing the evolutionary history of ecosystems and life at that time. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第15281号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Examination Committee Members: | (主査) 教授 沢田 健, 教授 永井 隆哉, 准教授 伊庭 靖弘, 助教 中村 英人 |
| Degree Affiliation: | 理学院（自然史科学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/89550 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 理学院(Graduate School of Science)
学位論文 (Theses) > 博士 （理学）
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