Triterpenoids and their derivatives are ubiquitous in sediment samples. Land plants are major sources of nonhopanoid triterpenoids; these terpenoids comprise a vast number of chemotaxonomically distinct biomolecules. Hence, geologically occurring plant-derived triterpenoids (geoterpenoids) potentially record unique characteristics of paleovegetation and sedimentary environments, and serve as source-specific markers for studying paleoenvironments. This review is aimed at explaining the origin of triterpenoids and their use as biomarkers in elucidating paleoenvironments. Herein, application of plant-derived triterpenoids is discussed in terms of: (i) their biosynthetic pathways. These compounds are primarily synthesized via oxidosqualene cyclase (OSCs) and serve as precursors for a variety of membrane sterols and steroid hormones. Studies on OSCs and resulting compounds have helped elucidate the diversity and origin of the parent terpenoids. (ii) their chemotaxonomic significance. Geochemically important classes of triterpenoid skeletons are useful in gathering and substantiating information on botanical origin of these compounds, evolution and diversification of angiosperms, and organic matter preservation during different periods in geological history. (iii) current knowledge on their transformation into geoterpenoids via diagenetic alterations. This knowledge helped in paleoenvironmental reconstructions from the local depositional environments to paleoclimatic variations. This review focuses on triterpenoids as paleoenvironmental biomarkers, and consolidates relevant literature that can form the basis for developing tools and techniques for improved paleoenvironment reconstruction. Future investigations should focus on detecting as yet unknown classes of triterpenoids and their biosynthetic pathways, inclusion of this information in automated databases, and identification of geoterpenoids as potential biomarkers to further our understanding of paleoenvironments and paleoclimate.
Trophic position (TP) of the daphnia Daphnia longispina and the copepod Acanthodiaptomus pacificus in an oligotrophic lake, Shirakoma-ike, was investigated via stable nitrogen isotope composition (15N/14N) analysis of amino acids, to understand the foraging strategy of these two dominant freshwater zooplankton species in an oligotrophic lake. The surface water of this lake is frozen in winter, and the life cycle and trophic behavior are different between these two species: the daphnia is found only in spring-autumn, whereas the copepod is found in whole season. In the present study, we found that the TP is 2.1±0.0 for the daphnia in spring-autumn and 2.3±0.3 for the copepod in whole season. These results reveal strong herbivory for the daphnia compared to dietary plasticity and facultative omnivory for the copepod. The latter is suggested to feed on phytoplankton for spring and autumn (TP=2.1±0.0) and on both phytoplankton and heterotrophic microbes (e.g., protists and bacteria) for summer and winter (TP=2.6±0.0). The foraging strategy is thus different between daphnia and copepods in this lake. This finding may explain why the daphnia is absent whereas the copepod is present in the frozen lake in winter where primary production is limited.
The parasitic nematode Anisakis is one of major parasites frequently found in fish, squid, and marine mammals including dolphins and whales, and cases severe abdominal pain if human eats infected fish or squid. However, little knowledge is available in what the parasites are doing in the host fish species and how they can survive and remain infective in their unique life cycles. In the present study, to enhance our knowledge on the parasite, we investigated trophic level (TL) and potential diet resources (δ15NResource) based on stable nitrogen isotopic composition (δ15N) of glutamic acid and phenylalanine in Anisakis larvae and their host fish Pleurogrammus azonus. The TL of Anisakis larvae (2.6-2.9) is considerably smaller than that of muscle in the host fish (3.6). Moreover, the δ15NResource values largely vary among individual Anisakis larvae specimens (2.4‰-4.7‰), and several specimens are clearly smaller than the value of muscle in the host fish (4.3‰). These results reveal that Anisakis larvae have never fed on the host fish tissues/organs even though they are found in the fish, and suggest that Anisakis larvae can survive as a dormant phase, remain infective, and be accumulated in the paratenic host fish for the effective infection to the definitive hosts.
Ring degraded triterpenoids, in which cyclic structure is opened and/or cleaved, were commonly identified in sediments and peats. These degraded triterpenoids such as des-A, des-E, and C ring-cleaved triterpenoids are considered to be formed by microbial and/or photochemical processes during transport and deposition. In the present study, we analyzed the ring degraded triterpenoids using GC-MS in the event deposits such as turbiditic sediments of the Miocene Kawabata Formation from Yubari, central Hokkaido, and a tsunami deposit in the Holocene peat core from Kiritappu area, eastern Hokkaido. We identified various des-A and des-E triterpenoids and C-ring cleaved triterpenoids including aliphatic and aromatic hydrocarbons as well as ketones. In addition, mass spectra of unidentified des-A triterpenoids were reported.