Nutritional sources of meio- and macrofauna at hydrothermal vents and adjacent areas: Natural-abundance radiocarbon and stable isotope analyses

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nomaki, H., Uejima, Y., Ogawa, N. O., Yamane, M., Watanabe, H. K., Senokuchi, R., Bernhard, J. M., Kitahashi, T., Miyairi, Y., Yokoyama, Y., Ohkouchi, N., & Shimanaga, M. Nutritional sources of meio- and macrofauna at hydrothermal vents and adjacent areas: Natural-abundance radiocarbon and stable isotope analyses. Marine Ecology Progress Series, 622, (2019): 49-65, doi:10.3354/meps13053.Deep-sea hydrothermal vents host unique marine ecosystems that rely on organic matter produced by chemoautotrophic microbes together with phytodetritus. Although meiofauna can be abundant at such vents, the small size of meiofauna limits studies on nutritional sources. Here we investigated dietary sources of meio- and macrofauna at hydrothermal vent fields in the western North Pacific using stable carbon and nitrogen isotope ratios (δ13C, δ15N) and natural-abundance radiocarbon (Δ14C). Bacterial mats and Paralvinella spp. (polychaetes) collected from hydrothermal vent chimneys were enriched in 13C (up to -10‰) and depleted in 14C (-700 to -580‰). The δ13C and Δ14C values of dirivultid copepods, endemic to hydrothermal vent chimneys, were -11‰ and -661‰, respectively, and were similar to the values in the bacterial mats and Paralvinella spp. but distinct from those of nearby non-vent sediments (δ13C: ~-24‰) and water-column plankton (Δ14C: ~40‰). In contrast, δ13C values of nematodes from vent chimneys were similar to those of non-vent sites (ca. -25‰). Results suggest that dirivultids relied on vent chimney bacterial mats as their nutritional source, whereas vent nematodes did not obtain significant nutrient amounts from the chemolithoautotrophic microbes. The Δ14C values of Neoverruca intermedia (vent barnacle) suggest they gain nutrition from chemoautotrophic microbes, but the source of inorganic carbon was diluted with bottom water much more than those of the Paralvinella habitat, reflecting Neoverruca’s more distant distribution from active venting. The combination of stable and radioisotope analyses on hydrothermal vent organisms provides valuable information on their nutritional sources and, hence, their adaptive ecology to chemosynthesis-based ecosystems.We are grateful to the crews and scientists of the R/V ‘Natsushima’ and the ROV ‘Hyper-Dolphin’ of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) during the NT12-10, NT13-09 and NT14-06 cruises, and the R/V ‘Kaimei’ and the KM-ROV of JAMSTEC during the KM-ROV training cruise. We thank Yuki Iwadate for her help on sample preparations and 2 anonymous reviewers and the editor, who provided helpful comments on an earlier version of this manuscript. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Scientific Research C 26440246 to M.S.), the Japan Society for the Promotion of Science (Invitational fellowships for research in Japan, S14032 to J.M.B.), the WHOI Robert W. Morse Chair for Excellence in Oceanography, and The Investment in Science Fund at WHOI

在来種ネズミモチと移入種トウネズミモチ(モクセイ科) の保全遺伝学的研究

Genetic introgression from introduced, non-native species into native populations is a growing challenge for biological conservation, and one that raises unique practical and ethical issues. Ligustrum lucidum is native to China, and cultivated or used in gardens in various areas in Japan. Recently, some studies reported that this species escaped from cultivated areas and was sympatric with L. japonicum. This indicates that L. japonicum faces the ecological and genetic risk of hybridization and introgression with non-native L. lucidum. Therefore, we examined whether hybridization between L. japonicum and the non-native L. lucidum has occurred in a coexisting population using phenological and molecular analyses. The phenological results indicate that there is very little overlap in the flowering times of the two species. Moreover, molecular analyses using PCR-RFLP of chloroplast and nuclear DNA sequences could not detect any hybridization or introgression of L. lucidum and L. japonicum in the population.移入種から在来種への遺伝子移入は生物学的保全のための懸念課題であり，実用的かつ倫理的な問題を提起している。中国原産のトウネズミモチ（Ligustrum lucidum）は日本の広い地域で園芸として栽植されているが逸出により分布を拡大しており，在来種のネズミモチ（L. japonicum）と同所的に生育していることが近年報告されている。このため，ネズミモチはトウネズミモチとの雑種形成や浸透交雑の生態学的リスクにさらされていると考えられる。そこで本研究では，在来種のネズミモチと移入種のトウネズミモチの間での雑種形成による遺伝的攪乱の有無を明らかにすることを目的として，開花期調査および分子遺伝学的調査を行った。開花期の調査結果より，両種の開花期がずれていることが明らかとなった。PCR-RFLP解析の結果，ネズミモチとトウネズミモチの間に交雑個体および浸透交雑個体を検出することはできなかったため，両種間での交雑は起こっていないと考えられる

Metal contamination in a sediment core from Osaka Bay during the last 400 years

Osaka Bay adjacent to the Kyoto–Osaka–Kobe metropolitan area was affected by severe metal pollution during the twentieth century; yet little is known about the trace metal sources and pre-industrial human activities. We have determined the elemental concentrations and zinc stable isotope ratios (δ⁶⁶Zn) in bulk sediments and the trace metal concentrations in chemical fractions of a 9-m-long sediment core from Osaka Bay. Our goals were (1) to reconstruct the historical trace metal contamination, and (2) to identify anthropogenic Zn sources and the solid phases of anthropogenic trace metals. The core provided a continuous environmental record of the last 2300 years based on radiocarbon dating of molluscan shells. Copper, Zn, and Pb showed an initial enrichment from the 1670s AD, which could be caused by human activities due to an increasing population. In agreement with previous findings, the trace metal concentrations slightly increased from the 1870s, strongly increased from the beginning of the twentieth century, and peaked around 1960 before environmental pollution control laws were enacted. Increasing trace metal concentrations in the acid-labile and reducible fractions obtained by the Community Bureau of Reference (BCR) sequential extraction procedure toward the surface indicate carbonates and Mn oxyhydroxides were the primary fractions for anthropogenic trace metals. The δ⁶⁶Zn values (1) were constant until the 1940s, suggesting that the average δ⁶⁶Zn of industrial sources was indistinguishable from that value of the natural background, (2) showed a slight decrease from the 1950s and remained constant until the present, and (3) fell in a binary mixing process between a lithogenic (~ + 0.27‰) and an anthropogenic endmember (~ + 0.17‰), the latter likely representing a mixture of various Zn sources such as road dust, tire wear, industrial effluents, and effluents from wastewater treatment plants. We conclude the combination of Zn stable isotopes together with chemical fractions obtained by the BCR method represents a promising approach to assess the trace metal sources and their potential mobility in sediment cores from anthropogenically affected coastal areas

Genetic differences between C57BL/6 substrains affect the process of testis differentiation in Y-POS mice

C57BL/6J-XYPOS (B6J-XYPOS) mice, which have the Y chromosome derived from Mus musculus poschiavinus on a B6J genetic background, form ovotestes or ovaries. Previously, we replaced the genetic background of B6J-XYPOS mice with B6N and found that individuals with testes also appeared in addition to those with ovaries or ovotestes. To investigate the effect of the B6J genetic sequence on the testis differentiation, the genetic background of B6N-XYPOS mice was replaced with B6J again. The recovery of the B6J genetic background significantly decreased the incidence of testes; only ovaries developed. These results indicate that the testicular differentiation process tends to be perturbed especially in the B6J substrain. This shows the importance of substrain differences in mice usually treated as B6 collectively

Advances in the application of amino acid nitrogen isotopic analysis in ecological and biogeochemical studies

Compound-specific isotopic analysis of amino acids (CSIA-AA) has emerged in the last decade as a powerful approach for tracing the origins and fate of nitrogen in ecological and biogeochemical studies. This approach is based on the empirical observation that source amino acids (SAAs) (i.e., phenylalanine), fractionate 15N very little (\u3c 0.5‰) during trophic transfer, whereas trophic AAs (TAAs) (i.e., glutamic acid), are greatly (∼6–8‰) enriched in 15N during each trophic step. The differential fractionation of these two AA groups can provide a valuable estimate of consumer trophic position that is internally indexed to the baseline δ15N value of the integrated food web. In this paper, we critically review the analytical methods for determining the nitrogen isotopic composition of AAs by gas chromatography–isotope-ratio mass spectrometry. We also discuss methodological considerations for accurate trophic position assessment of organisms using CSIA-AA. We then discuss the advantages and challenges of the CSIA-AA approach using published case studies across a range of topics, including trophic position assessment in various ecosystems, reconstruction of ancient human diets, reconstruction of animal migration and environmental variability, and assessment of marine organic matter dynamics with new classification of microbial fractionation patterns. It is clear that the CSIA-AA approach can provide unique insight into the sources, cycling, and trophic modification of organic nitrogen as it flows through systems. However, this approach will be greatly improved through continued exploration into how biochemical, physiological, and ecological mechanisms affect isotopic fractionation of individual AAs. We end this review with a perspective on future work that will promote the evolution of the rapidly growing field of CSIA-AA