Reframing the Mammoth Steppe: Examining Mammoth Steppe Ecology Using Carbon and Nitrogen Isotopic Compositions of Megafauna Collagen

The Pleistocene mammoth steppe was a vast biome that stretched from northwestern Europe to central Canada. A diverse set of megaherbivore and megacarnivore species lived within this biome and there was significant ecosystem faunal and floral homogeneity. At the end of the Pleistocene, this biome disappeared, with the extinction or extirpation of many of the megafaunal species that inhabited it. This thesis reconstructs the ecology of the mammoth steppe using the isotopic compositions of carbon and nitrogen from megafaunal collagen. The reconstruction is done at a variety of ecological scales, beginning with individual animal- and season-specific isotopic studies of antlers, and then comparison to bones from the same species. This provides a framework to understand the habitat and diet of antlered species through the Pleistocene and into the Holocene. Non-ruminant species ecology is assessed using the carbon and nitrogen isotopic compositions of the individual amino acids that comprise their bulk collagen. The compound-specific technique allows metabolic and habitat or dietary effects to be separated and diets to be classified. These studies indicate woolly mammoths ate a distinct diet, likely comprising decayed plants, and that some horses shared this dietary niche. The Pleistocene giant beaver consumed aquatic plants, while the mastodon consumed unmodified terrestrial plant material. Finally, the bulk collagen isotopic compositions measured in this work as well as reviewed from the literature are compiled and the mathematical tool SIBER (Stable Isotope Bayesian Ellipses in R) is used to define the isotopic niche for multiple megaherbivore species at different times and sites across the mammoth steppe. This, combined with the dietary and habitat information gleaned from the antler and amino acid isotopic measurements, allows an in-depth analysis of mammoth steppe ecology. Before the LGM (Last Glacial Maximum), most species occupied consistent isotopic niches between sites across the mammoth steppe, suggesting consistent diets or habitats during the pre-LGM period. These isotopic niche patterns changed during the LGM, and the patterns were not re-established post-LGM or in the Holocene. These changes suggest that the ecosystem suffered a major disturbance during the LGM, before the extinctions that occurred at the end of the Pleistocene

Solving the woolly mammoth conundrum: amino acid 15N-enrichment suggests a distinct forage or habitat

Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions. Previous isotopic studies of mammoths’ diet and physiology have been hampered by the ‘mammoth conundrum’: woolly mammoths have anomalously high collagen δ15N values, which are more similar to coeval carnivores than herbivores and which could imply a distinct diet and (or) habitat, or a physiological adaptation. We analyzed individual amino acids from collagen of adult woolly mammoths and coeval species and discovered greater  15N enrichment in source amino acids of woolly mammoths than in most other herbivores or carnivores. Woolly mammoths consumed an isotopically distinct food source, reflective of extreme aridity, dung fertilization and (or) plant selection. This dietary signal suggests that woolly mammoths occupied a distinct habitat or forage niche relative to other Pleistocene herbivores

Reframing the mammoth steppe: Insights from analysis of isotopic niches

Woolly mammoth (Mammuthus primigenius), horse (Equus spp.) and bison (Bison spp.) coexisted with a variety of mammalian megafauna across the Pleistocene mammoth steppe – a megacontinental ecosystem that spanned northern Eurasia and northwestern North America. Previous research has suggested that highly conserved niches with minimal niche overlap allowed high levels of species diversity on the mammoth steppe. Here we evaluate previously published and some new collagen carbon and nitrogen isotope data (δ13C, δ15N) for mammoth steppe megaherbivores using Stable Isotope Bayesian Ellipses in R (SIBER) and linear regression models to determine isotopic niches for individual species during broad time intervals (pre-, during and post-Last Glacial Maximum (LGM)) at multiple geographic regions across the mammoth steppe. Individual species maintained relatively consistent isotopic niche positions at different geographic locations and during different times. Diet and habitat niches for any given species appear to have been similar across the mammoth steppe. Between some regions and times, however, species' isotopic niches changed, suggesting adaptation to local climatic conditions and/or changes in the nitrogen isotope patterns at the base of the food web. Isotopic niche overlap, including at the level of core niche overlap (>60% overlap), was observed in at least one time and region for most species. This overlap suggests high levels of functional redundancy in the ecosystem, whereby one species could fulfil another's ecological role in the latter's absence. Despite spatial and temporal environmental variation, species' adaptability and functional redundancy within the ecosystem would have made the mammoth steppe a highly resilient ecosystem

Seasonal paleoecological records from antler collagen δ13C and δ15N

Cervids living in high latitudes have evolved to thrive in ecosystems that experience dramatic seasonal changes. Understanding these seasonal adaptations is important for reconstructing cervid life histories, ecosystem dynamics and responses in the distant and not-so-distant past to changing seasonality caused by climate change. Cervid antlers provide a rare opportunity for insight into faunal seasonal ecology, as they are grown and shed each year. Stable isotopes of carbon and nitrogen measured directly from antlers have the potential to provide seasonal dietary data for individuals. If the isotopic signals in bone and antler are controlled by the same metabolic processes, then the stable carbon and nitrogen isotope compositions of collagen (δ13CColl and δ15NColl) from incrementally grown antler tissue provide time-constrained dietary signals from the spring and summer growth season. Bone, by comparison, provides an average signal over several years. The amino acid (glutamate and phenylalanine) δ15N in antlers from modern captive caribou showed similar trophic discrimination factors to earlier results for other collagenous tissues (bone, tooth dentin and cementum). Hence, growth rate was not the primary control on the stable isotope composition of antler collagen. We applied this knowledge to assess seasonal shifts in Quaternary fossils of three Cervidae species: elk (Cervus elaphus), moose (Alces alces), and caribou (Rangifer tarandus). Paired antler-bone δ13CColl and δ15NColl from the same individual were used to identify differences between summer and annual diet and ecology. Intra-antler isotopic variability from serially sampled antlers was used to examine seasonal dietary shifts and specialization

Analysis of non-derivatized bacteriohopanepolyols using UHPLC-HRMS reveals great structural diversity in environmental lipid assemblages

Bacteriohopanepolyols (BHPs) are lipids with great chemotaxonomic potential for microbial populations and biogeochemical processes in the environment. The most commonly used methods for BHP analysis are chemical degradation followed by gas chromatography-mass spectrometry (MS) or derivatization followed by high performance liquid chromatography (HPLC)- atmospheric pressure chemical ionization/MS. Here we report on significant advances in the analysis of non-derivatized BHPs using U(ltra)HPLC-electrospray ionization-high resolution MS2. Fragmentation mass spectra provided information on the BHP core, functionalized side chain, as well as the conjugated moiety of composite BHPs. We successfully identified the common bacteriohopanepolyols and their (di)methylated and (di)unsaturated homologues, aminoBHPs, and composite BHPs (e.g., cyclitol ethers and methylcarbamateBHPs) in biomass of several known BHP-producing micro-organisms. To show how the method can be exploited to reveal the diversity of BHPs in the environment, we investigated a soil from an active methane seep, in which we detected ca. 130 individual BHPs, including a complex distribution of adenosylhopanes. We identified the nucleoside base moiety of both adenosylhopane type-2 and type-3. Adenosyl hopane type-3 contains a methylated adenine as its nucleobase, while type-2 appears to contain a deaminated and methylated adenine, or N1-methylinosine. In addition, we detected novel adenosylhopanes. Furthermore, we identified a novel series of composite BHPs comprising of bacteriohopanepolyols conjugated to an ethenolamine moiety. The novel ethanolamineBHPs as well as aminoBHPs were also detected acylated to fatty acids. The analytical approach described allows for simultaneous analysis of the full suite of IPLs, now including BHPs, and represents a further step towards environmental lipidomics

A unique bacteriohopanetetrol stereoisomer of marine anammox

Anaerobic ammonium oxidation (anammox) is a major process of bioavailable nitrogen removal from marine systems. Previously, a bacteriohopanetetrol (BHT) isomer, with unknown stereochemistry, eluting later than BHT using high performance liquid chromatography (HPLC), was detected in ‘Ca. Scalindua profunda’ and proposed as a biomarker for anammox in marine paleo-environments. However, the utility of this BHT isomer as an anammox biomarker is hindered by the fact that four other, non-anammox bacteria are also known to produce a late-eluting BHT stereoisomer. The stereochemistry in Acetobacter pasteurianus, Komagataeibacter xylinus and Frankia sp. was known to be 17β, 21β(H), 22R, 32R, 33R, 34R (BHT-34R). The stereochemistry of the late-eluting BHT in Methylocella palustris was unknown. To determine if marine anammox bacteria produce a unique BHT isomer, we studied the BHT distributions and stereochemistry of known BHT isomer producers and of previously unscreened marine (‘Ca. Scalindua brodeae’) and freshwater (‘Ca. Brocadia sp.’) anammox bacteria using HPLC and gas chromatographic (GC) analysis of acetylated BHTs and ultra high performance liquid chromatography (UHPLC)-high resolution mass spectrometry (HRMS) analysis of non-acetylated BHTs. The 34R stereochemistry was confirmed for the BHT isomers in Ca. Brocadia sp. and Methylocella palustris. However, ‘Ca. Scalindua sp.’ synthesise a stereochemically distinct BHT isomer, with still unconfirmed stereochemistry (BHT-x). Only GC analysis of acetylated BHT and UHPLC analysis of non-acetylated BHT distinguished between late-eluting BHT isomers. Acetylated BHT-x and BHT-34R co-elute by HPLC. As BHT-x is currently only known to be produced by ‘Ca. Scalindua spp.’, it may be a biomarker for marine anammox

University student-led public engagement event: increasing audience diversity and impact in a non-science space

There is a wealth of innovation in microbiology outreach events globally, including in the setting where the public engagement is hosted. Previous data indicate an underrepresentation of marginalized ethnic groups attending UK science-based public engagement events. This project engaged our student cohort, encompassing a diverse range of ethnic groups, to create an integrated art and science event within an existing series of adult education evenings. The study’s objectives were to increase the proportion of visitors from marginalized ethnic groups and to gain a greater understanding of the impact of the event on the visitors’ reported science capital. The participants’ demographics, links to our students and University, and detailed impact on participants’ science capital of the event were determined through analysis of exit questionnaires. There was an increase in the proportion of marginalized ethnic group visitors compared to similar previous events. A higher proportion of visitors from marginalized ethnic groups had links with our students and University compared to white/white British visitors. Elements of the exit questionnaire were mapped to the science capital framework and participants’ science capital was determined. Both ethnically marginalized participants and white/white British visitors showed an increase in science capital, specifically dimensions of science-related social capital and science-related cultural capital, after the event. In conclusion, our study suggests that a student-led blended art and science public engagement can increase the ethnic diversity of those attending and can contribute towards creating more inclusive public engagement events.</jats:p

Student-led public engagement event: increasing audience diversity and impact in a non-science space

There is a wealth of innovation in microbiology outreach events globally, including in the setting where the public engagement is hosted. Previous data indicates underrepresentation of marginalised ethnic groups attending UK science-based public engagement events. This project engaged our student cohort, encompassing a diverse range of ethnic groups, to create an integrated art and science event within an existing series of adult education evenings. The study’s objectives were to increase the proportion of visitors from marginalised ethnic groups and to gain a greater understanding of the impact of the event on the visitors’ reported science capital. The participants' demographics, links to our students and University, and detailed impact on participants' science capital of the event were determined through analysis of exit questionnaires. There was an increase in the proportion of marginalised ethnic group visitors compared to similar previous events. A higher proportion of visitors from marginalised ethnic groups had links with our students and University compared to white/white British visitors. Elements of the exit-questionnaire were mapped to the science capital framework and participants' science capital determined. Both ethnically marginalised participants and white/white British visitors showed an increase in science capital, specifically dimensions of science-related social capital and science-related cultural capital, after the event. In conclusion, our study suggests that a student-led blended art and science public engagement can increase the ethnic diversity of those attending and can contribute towards creating more inclusive public engagement events.</jats:p

Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)

In response to rising CO2concentrations and increasing global sea surface temperatures,oxygen minimum zones (OMZ), or“dead zones”, are expected to expand. OMZs are fueled by highprimary productivity, resulting in enhanced biological oxygen demand at depth, subsequent oxygen depletion, and attenuation of remineralization. This results in the deposition of organic carbon‐rich sediments. Carbon drawdown is estimated by biogeochemical models; however, a major process is ignored: carbon fixation in the mid‐and lower water column. Here, we show that chemoautotrophic carbon fixation is important in the Arabian Sea OMZ; and manifests in a13C‐depleted signature of sedimentary organic carbon. We determined theδ13C values of Corg deposited in close spatial proximity but over a steepbottom‐water oxygen gradient, and theδ13C composition of biomarkers of chemoautotrophic bacteriacapable of anaerobic ammonia oxidation (anammox). Isotope mixing models show that detritus fromanammox bacteria or other chemoautotrophs likely forms a substantial part of the organic matter depositedwithin the Arabian Sea OMZ (~17%), implying that the contribution of chemoautotrophs to settling organicmatter is exported to the sediment. This has implications for the evaluation of past, and future, OMZs:biogeochemical models that operate on the assumption that all sinking organic matter is photosynthetically derived, without new addition of carbon, could significantly underestimate the extent of remineralization. Oxygen demand in oxygen minimum zones could thus be higher than projections suggest, leading to a more intense expansion of OMZs than expected