Stable Southern Hemisphere westerly winds throughout the Holocene until intensification in the last two millennia

The Southern Hemisphere westerly winds sustain the Southern Ocean’s role as one of Earth’s main carbon sinks, and have helped sequester nearly half the anthropogenic CO2 stored in the ocean. Observations show shifts in the vigor of this climate regulator, but models disagree how future change impacts carbon storage due to scarce baseline data. Here, we use the hydrogen isotope ratios of sedimentary lipids to resolve Holocene changes in Southern Hemisphere westerly wind strength. Our reconstruction reveals stable values until ~2150 years ago when aquatic compounds became more 2H-enriched. We attribute this isotope excursion to wind-driven lake water evaporation, and regional paleoclimate evidence shows it marks a trend towards a negative Southern Annular Mode – the Southern Ocean’s main mode of atmospheric variability. Because this shift is unmatched in the past 7000 years, our findings suggest that previously published millennium-long Southern Annular Mode indices used to benchmark future change may not capture the full range of natural variability.publishedVersio

Holocene changes in the position of the Southern Hemisphere Westerlies recorded by long-distance transport of pollen to the Kerguelen Islands

The Southern Hemisphere Westerlies (SHW) are a vital part of the Southern Hemisphere's coupled ocean-atmosphere system and play an important role in the global climate system. The SHW affect the upwelling of carbon-rich deep water and exchange of CO2 from the ocean to the atmosphere by driving the Antarctic Circumpolar Current. On seasonal to millennial timescales, changes in the strength and position of the SHW are associated with temperature and precipitation changes throughout the extratropical Southern Hemisphere. Understanding the behaviour of the SHW under different background climate states is important for anticipating its future behaviour and remains a subject of ongoing research. Terrestrial paleoclimate records from lake sediments are valuable for reconstructing past atmospheric change and records from the handful of sub-Antarctic islands provide the opportunity to develop datasets to document spatio-temporal patterns of long-term SHW behaviour. Here, we generate palynological, microcharcoal, and sedimentological reconstructions (including CT imagery, μXRF analysis, magnetic susceptibility, and loss-on-ignition) on lake sediments from the Kerguelen Islands (49°S) to constrain variability in Holocene vegetation, climate, and atmospheric circulation (SHW position). Due to the influence of the SHW on the Kerguelen Islands, the influx of long-distance transported (LDT) pollen and microcharcoal from southern Africa serve as proxies for the meridional position of the SHW. In contrast with the stable conditions that prevailed on the Kerguelen Islands over the past 8,600 cal yr BP, our findings reveal a highly dynamic Early Holocene period. Consistent with local palynological evidence of warmer conditions, a high influx of LDT pollen and charcoal from southern Africa suggest that the SHW core belt was located further south of the Kerguelen Islands during this time. Comparison against paleoclimate records from the surrounding region and beyond suggests that the inferred changes might be explained by changes to our planet's interhemispheric thermal gradient, triggered by North Atlantic cooling in response to melting of the last remnants of the Laurentide Ice Sheet.publishedVersio

Tools for better SLM knowledge management and informed decision-making in addressing land degradation at different scales: the WOCAT–LADA–DESIRE methodology

Desertification research conventionally focuses on the problem – that is, degradation – while neglecting the appraisal of successful conservation practices. Based on the premise that Sustainable Land Management (SLM) experiences are not sufficiently or comprehensively documented, evaluated, and shared, the World Overview of Conservation Approaches and Technologies (WOCAT) initiative (www.wocat.net), in collaboration with FAO’s Land Degradation Assessment in Drylands (LADA) project (www.fao.org/nr/lada/) and the EU’s DESIRE project (http://www.desire-project.eu/), has developed standardised tools and methods for compiling and evaluating the biophysical and socio-economic knowledge available about SLM. The tools allow SLM specialists to share their knowledge and assess the impact of SLM at the local, national, and global levels. As a whole, the WOCAT–LADA–DESIRE methodology comprises tools for documenting, self-evaluating, and assessing the impact of SLM practices, as well as for knowledge sharing and decision support in the field, at the planning level, and in scaling up identified good practices. SLM depends on flexibility and responsiveness to changing complex ecological and socioeconomic causes of land degradation. The WOCAT tools are designed to reflect and capture this capacity of SLM. In order to take account of new challenges and meet emerging needs of WOCAT users, the tools are constantly further developed and adapted. Recent enhancements include tools for improved data analysis (impact and cost/benefit), cross-scale mapping, climate change adaptation and disaster risk management, and easier reporting on SLM best practices to UNCCD and other national and international partners. Moreover, WOCAT has begun to give land users a voice by backing conventional documentation with video clips straight from the field. To promote the scaling up of SLM, WOCAT works with key institutions and partners at the local and national level, for example advisory services and implementation projects. Keywords: Sustainable Land Management (SLM), knowledge management, decision-making, WOCAT–LADA–DESIRE methodology

Behaviourally modern humans in coastal southern Africa experienced an increasingly continental climate during the transition from Marine Isotope Stage 5 to 4

Unravelling evolution-by-environment interactions on the gut microbiome is particularly relevant considering the unprecedented level of human-driven disruption of the ecological and evolutionary trajectories of species. Here, we aimed to evaluate whether an evolutionary response to size-selective mortality influences the gut microbiome of medaka (Oryzias latipes), how environmental conditions interact with the genetic background of medaka on their microbiota, and the association between microbiome diversity and medaka growth-related traits. To do so, we studied two lineages of medaka with known divergence in foraging efficiency and life history raised under antagonistic size-selective regimes for 10 generations (i.e. the largest or the smallest breeders were removed to mimic fishing-like or natural mortality). In pond mesocosms, the two lineages were subjected to contrasting population density and light intensity (used as proxies of resource availability). We observed significant differences in the gut microbiome composition and richness between the two lines, and this effect was mediated by light intensity. The bacterial richness of fishing-like medaka (small-breeder line) was reduced by 34% under low-light conditions compared to high-light conditions, while it remained unchanged in natural mortality-selected medaka (large-breeder line). However, the observed changes in bacterial richness did not correlate with changes in adult growth-related traits. Given the growing evidence about the gut microbiomes importance to host health, more in-depth studies are required to fully understand the role of the microbiome in size-selected organisms and the possible ecosystem-level consequences.publishedVersio

Evolution of the deaminase fold and multiple origins of eukaryotic editing and mutagenic nucleic acid deaminases from bacterial toxin systems

The deaminase-like fold includes, in addition to nucleic acid/nucleotide deaminases, several catalytic domains such as the JAB domain, and others involved in nucleotide and ADP-ribose metabolism. Using sensitive sequence and structural comparison methods, we develop a comprehensive natural classification of the deaminase-like fold and show that its ancestral version was likely to operate on nucleotides or nucleic acids. Consequently, we present evidence that a specific group of JAB domains are likely to possess a DNA repair function, distinct from the previously known deubiquitinating peptidase activity. We also identified numerous previously unknown clades of nucleic acid deaminases. Using inference based on contextual information, we suggest that most of these clades are toxin domains of two distinct classes of bacterial toxin systems, namely polymorphic toxins implicated in bacterial interstrain competition and those that target distantly related cells. Genome context information suggests that these toxins might be delivered via diverse secretory systems, such as Type V, Type VI, PVC and a novel PrsW-like intramembrane peptidase-dependent mechanism. We propose that certain deaminase toxins might be deployed by diverse extracellular and intracellular pathogens as also endosymbionts as effectors targeting nucleic acids of host cells. Our analysis suggests that these toxin deaminases have been acquired by eukaryotes on several independent occasions and recruited as organellar or nucleo-cytoplasmic RNA modifiers, operating on tRNAs, mRNAs and short non-coding RNAs, and also as mutators of hyper-variable genes, viruses and selfish elements. This scenario potentially explains the origin of mutagenic AID/APOBEC-like deaminases, including novel versions from Caenorhabditis, Nematostella and diverse algae and a large class of fast-evolving fungal deaminases. These observations greatly expand the distribution of possible unidentified mutagenic processes catalyzed by nucleic acid deaminases

The Zinc Dyshomeostasis Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Hallmark AD neuropathology includes extracellular amyloid plaques composed largely of the amyloid-β protein (Aβ), intracellular neurofibrillary tangles (NFTs) composed of hyper-phosphorylated microtubule-associated protein tau (MAP-tau), and microtubule destabilization. Early-onset autosomal dominant AD genes are associated with excessive Aβ accumulation, however cognitive impairment best correlates with NFTs and disrupted microtubules. The mechanisms linking Aβ and NFT pathologies in AD are unknown. Here, we propose that sequestration of zinc by Aβ-amyloid deposits (Aβ oligomers and plaques) not only drives Aβ aggregation, but also disrupts zinc homeostasis in zinc-enriched brain regions important for memory and vulnerable to AD pathology, resulting in intra-neuronal zinc levels, which are either too low, or excessively high. To evaluate this hypothesis, we 1) used molecular modeling of zinc binding to the microtubule component protein tubulin, identifying specific, high-affinity zinc binding sites that influence side-to-side tubulin interaction, the sensitive link in microtubule polymerization and stability. We also 2) performed kinetic modeling showing zinc distribution in extra-neuronal Aβ deposits can reduce intra-neuronal zinc binding to microtubules, destabilizing microtubules. Finally, we 3) used metallomic imaging mass spectrometry (MIMS) to show anatomically-localized and age-dependent zinc dyshomeostasis in specific brain regions of Tg2576 transgenic, mice, a model for AD. We found excess zinc in brain regions associated with memory processing and NFT pathology. Overall, we present a theoretical framework and support for a new theory of AD linking extra-neuronal Aβ amyloid to intra-neuronal NFTs and cognitive dysfunction. The connection, we propose, is based on β-amyloid-induced alterations in zinc ion concentration inside neurons affecting stability of polymerized microtubules, their binding to MAP-tau, and molecular dynamics involved in cognition. Further, our theory supports novel AD therapeutic strategies targeting intra-neuronal zinc homeostasis and microtubule dynamics to prevent neurodegeneration and cognitive decline