Reconstructing Hominin Diets with Stable Isotope Analysis of Amino Acids: New Perspectives and Future Directions.

Stable isotope analysis of teeth and bones is regularly applied by archeologists and paleoanthropologists seeking to reconstruct diets, ecologies, and environments of past hominin populations. Moving beyond the now prevalent study of stable isotope ratios from bulk materials, researchers are increasingly turning to stable isotope ratios of individual amino acids to obtain more detailed and robust insights into trophic level and resource use. In the present article, we provide a guide on how to best use amino acid stable isotope ratios to determine hominin dietary behaviors and ecologies, past and present. We highlight existing uncertainties of interpretation and the methodological developments required to ensure good practice. In doing so, we hope to make this promising approach more broadly accessible to researchers at a variety of career stages and from a variety of methodological and academic backgrounds who seek to delve into new depths in the study of dietary composition.

Chemical Modification of Biomarkers through Accelerated Degradation: Implications for Ancient Plant Identification in Archaeo-Organic Residues.

Biochemical and biomolecular archaeology is increasingly used to elucidate the consumption, use, origin, and trade of plants in the past. However, it can be challenging to use biomarkers to identify the taxonomic origin of archaeological plants due to limited knowledge of molecular survival and degradation for many key plant compounds in archaeological contexts. To gain a fundamental understanding of the chemical alterations associated with chemical degradation processes in ancient samples, we conducted accelerated degradation experiments with essential oil derived from cedar (Cedrus atlantica) exposed to materials commonly found in the archaeological record. Using GC-MS and multivariate analysis, we detected a total of 102 compounds across 19 treatments that were classified into three groups. The first group comprised compounds that were abundant in fresh cedar oil but would be unlikely to remain in ancient residues due to rapid degradation. The second group consisted of compounds that remained relatively stable or increased over time, which could be potential biomarkers for identifying cedar in archaeological residues. Compounds in the third group were absent in fresh cedar oil but were formed during specific experiments that could be indicative for certain storage conditions. These results show that caution is warranted for applying biomolecular profiles of fresh plants to ancient samples and that carefully designed accelerated degradation experiments can, at least in part, overcome this limitation.

Higher sea surface temperature in the Indian Ocean during the Last Interglacial weakened the South Asian monsoon.

SignificanceUnderstanding the drivers of South Asian monsoon intensity is pivotal for improving climate forecasting under global warming scenarios. Solar insolation is assumed to be the dominant driver of monsoon variability in warm climate regimes, but this has not been verified by proxy data. We report a South Asian monsoon rainfall record spanning the last ∼130 kyr in the Ganges-Brahmaputra-Meghna river catchment. Our multiproxy data reveal that the South Asian monsoon was weaker during the Last Interglacial (130 to 115 ka)-despite higher insolation-than during the Holocene (11.6 ka to present), thus questioning the widely accepted model assumption. Our work implies that Indian Ocean warming may increase the occurrence of severe monsoon failures in South Asia.

Ostrich eggshell beads reveal 50,000-year-old social network in Africa.

Humans evolved in a patchwork of semi-connected populations across Africa1,2; understanding when and how these groups connected is critical to interpreting our present-day biological and cultural diversity. Genetic analyses reveal that eastern and southern African lineages diverged sometime in the Pleistocene epoch, approximately 350-70 thousand years ago (ka)3,4; however, little is known about the exact timing of these interactions, the cultural context of these exchanges or the mechanisms that drove their separation. Here we compare ostrich eggshell bead variations between eastern and southern Africa to explore population dynamics over the past 50,000 years. We found that ostrich eggshell bead technology probably originated in eastern Africa and spread southward approximately 50-33 ka via a regional network. This connection breaks down approximately 33 ka, with populations remaining isolated until herders entered southern Africa after 2 ka. The timing of this disconnection broadly corresponds with the southward shift of the Intertropical Convergence Zone, which caused periodic flooding of the Zambezi River catchment (an area that connects eastern and southern Africa). This suggests that climate exerted some influence in shaping human social contact. Our study implies a later regional divergence than predicted by genetic analyses, identifies an approximately 3,000-kilometre stylistic connection and offers important new insights into the social dimension of ancient interactions.

'Emptying Forests?' Conservation Implications of Past Human-Primate Interactions.

Non-human primates are among the most vulnerable tropical animals to extinction and ~50% of primate species are endangered. Human hunting is considered a major cause of increasingly 'empty forests', yet archaeological data remains under-utilised in testing this assertion over the longer-term. Zooarchaeological datasets allow investigation of human exploitation of primates and the reconstruction of extinction, extirpation, and translocation processes. We evaluate the application and limitations of data from zooarchaeological studies spanning the past 45 000 years in South and Southeast Asia in guiding primate conservation efforts. We highlight that environmental change was the primary threat to many South and Southeast Asian non-human primate populations during much of the Holocene, foreshadowing human-induced land-use and environmental change as major threats of the 21st century.

Earthquake and typhoon trigger unprecedented transient shifts in shallow hydrothermal vents biogeochemistry.

Shallow hydrothermal vents are of pivotal relevance for ocean biogeochemical cycles, including seawater dissolved heavy metals and trace elements as well as the carbonate system balance. The Kueishan Tao (KST) stratovolcano off Taiwan is associated with numerous hydrothermal vents emitting warm sulfur-rich fluids at so-called White Vents (WV) and Yellow Vent (YV) that impact the surrounding seawater masses and habitats. The morphological and biogeochemical consequences caused by a M5.8 earthquake and a C5 typhoon ("Nepartak") hitting KST (12th May, and 2nd-10th July, 2016) were studied within a 10-year time series (2009-2018) combining aerial drone imagery, technical diving, and hydrographic surveys. The catastrophic disturbances triggered landslides that reshaped the shoreline, burying the seabed and, as a consequence, native sulfur accretions that were abundant on the seafloor disappeared. A significant reduction in venting activity and fluid flow was observed at the high-temperature YV. Dissolved Inorganic Carbon (DIC) maxima in surrounding seawater reached 3000-5000 µmol kg-1, and Total Alkalinity (TA) drawdowns were below 1500-1000 µmol kg-1 lasting for one year. A strong decrease and, in some cases, depletion of dissolved elements (Cd, Ba, Tl, Pb, Fe, Cu, As) including Mg and Cl in seawater from shallow depths to the open ocean followed the disturbance, with a recovery of Mg and Cl to pre-disturbance concentrations in 2018. The WV and YV benthic megafauna exhibited mixed responses in their skeleton Mg:Ca and Sr:Ca ratios, not always following directions of seawater chemical changes. Over 70% of the organisms increased skeleton Mg:Ca ratio during rising DIC (higher CO2) despite decreasing seawater Mg:Ca ratios showing a high level of resilience. KST benthic organisms have historically co-existed with such events providing them ecological advantages under extreme conditions. The sudden and catastrophic changes observed at the KST site profoundly reshaped biogeochemical processes in shallow and offshore waters for one year, but they remained transient in nature, with a possible recovery of the system within two years.

13C values of glycolytic amino acids as indicators of carbohydrate utilization in carnivorous fish.

BACKGROUND: Stable isotope analysis of single amino acids (AA) is usually applied in food web studies for tracing biosynthetic origins of AA carbon backbones and establishing trophic positions of consumers, but the method is also showing promise for characterizing quantity and quality of dietary lipids and carbohydrates. METHODS: To investigate whether changes in high- and low-digestible carbohydrates affect δ 13C values of glycolytic AA, i.e., AA carbon backbones sourced from the glycolytic pathway, we compared Atlantic salmon (Salmo salar) from a feeding experiment with and without dietary inclusion of the red macroalga Palmaria palmata. The Control and experimental diets had similar relative proportions of macronutrients, but their ingredients differed; in the experimental treatment, 15% Palmaria inclusion substituted proteins from fishmeal and carbohydrates from corn starch. RESULTS: We found that 13C values of the glycolytic AA were highly sensitive to substitution of corn starch with Palmaria. The δ 13C offsets of glycolytic AA between salmon and their diets were significantly greater in the Palmaria inclusion than Control treatment. This greater offset can be attributed to the different utilization of high- vs. low-digestible carbohydrate sources, i.e., corn starch vs. Palmaria, in the two treatments, and metabolic routing of dietary lipids. In addition, similar δ 13C values of essential AA between treatments indicate similar nutrient assimilation efficiency for all terrestrial (pea protein concentrate and wheat gluten meal) and marine (fishmeal and red alga) derived protein sources. These results show that δ 13CAA analysis is a promising tool for improving our understanding of how carnivorous fish utilize macronutrient and route metabolic intermediates to tissue.

Know your fish: A novel compound-specific isotope approach for tracing wild and farmed salmon.

The rapid expansion of the aquaculture industry with carnivorous fish such as salmon has been accompanied by an equally rapid development in alternative feed ingredients. This has outpaced the ability of prevailing authentication method to trace the diet and origins of salmon products at the retail end. To close this gap, we developed a new profiling tool based on amino acid δ13C fingerprints. With this tool, we discriminated with high-accuracy among wild-caught, organically, and conventionally farmed salmon groups, as well as salmon fed alternative diets such as insects and macroalgae. Substitution of fishmeal with macroalgae was detected at 5% difference level. The δ13C fingerprints of essential amino acids appear particularly well suited for tracing protein sources, and the non-essentials for tracing lipid origins (terrestrial vs. aquatic). In an industry constantly developing new feed proteins and functional additives, our method is a promising tool for tracing salmon and other seafood products.

The dominant detritus-feeding invertebrate in Arctic peat soils derives its essential amino acids from gut symbionts.

Supplementation of nutrients by symbionts enables consumers to thrive on resources that might otherwise be insufficient to meet nutritional demands. Such nutritional subsidies by intracellular symbionts have been well studied; however, supplementation of de novo synthesized nutrients to hosts by extracellular gut symbionts is poorly documented, especially for generalists with relatively undifferentiated intestinal tracts. Although gut symbionts facilitate degradation of resources that would otherwise remain inaccessible to the host, such digestive actions alone cannot make up for dietary insufficiencies of macronutrients such as essential amino acids (EAA). Documenting whether gut symbionts also function as partners for symbiotic EAA supplementation is important because the question of how some detritivores are able to subsist on nutritionally insufficient diets has remained unresolved. To answer this poorly understood nutritional aspect of symbiont-host interactions, we studied the enchytraeid worm, a bulk soil feeder that thrives in Arctic peatlands. In a combined field and laboratory study, we employed stable isotope fingerprinting of amino acids to identify the biosynthetic origins of amino acids to bacteria, fungi and plants in enchytraeids. Enchytraeids collected from Arctic peatlands derived more than 80% of their EAA from bacteria. In a controlled feeding study with the enchytraeid Enchytraeus crypticus, EAA derived almost exclusively from gut bacteria when the worms fed on higher fibre diets, whereas most of the enchytraeids' EAA derived from dietary sources when fed on lower fibre diets. Our gene sequencing results of gut microbiota showed that the worms harbour several taxa in their gut lumen absent from their diets and substrates. Almost all gut taxa are candidates for EAA supplementation because almost all belong to clades capable of biosynthesizing EAA. Our study provides the first evidence of extensive symbiotic supplementation of EAA by microbial gut symbionts and demonstrates that symbiotic bacteria in the gut lumen appear to function as partners both for symbiotic EAA supplementation and for digestion of insoluble plant fibres.

The influence of diet and water on the stable oxygen and hydrogen isotope composition of Chironomidae (Diptera) with paleoecological implications.

Stable oxygen and hydrogen isotope analyses of fossil aquatic organisms, such as the chitinous head capsules of chironomid larvae (Chironomidae: Diptera), are promising proxies for inferring paleoecological conditions. In order for analyses of stable oxygen (delta(18)O) and hydrogen isotope ratios (delta(2)H) of fossil chironomid head capsules to be used effectively in paleoecological research, it is necessary to understand the factors controlling their stable oxygen and hydrogen composition. We cultured chironomid larvae in two isotopically distinct waters under controlled, replicated laboratory conditions. Chironomid larvae were fed on identical diets, to examine the degree to which water and diet influence the delta(18)O and delta(2)H of these organisms. We used a two-end member mixing model to determine the proportional contributions of oxygen and hydrogen from water to the oxygen and hydrogen of chironomid larvae. Our experiment demonstrated that 69.0 +/- 0.4% of oxygen and 30.8 +/- 2.6% of hydrogen in chironomid larvae are derived from habitat water. Our results show that oxygen isotopes from chironomid remains can better constrain past habitat water isotopic changes compared to hydrogen, due to 69% of the chironomid oxygen being influenced by habitat water. Our data add to a small but growing suite of comparative data on the sources of oxygen and hydrogen in animal tissues, and provide the first such analyses from aquatic insects.