Structure of bone in the skulls of Neanderthal fossils

Close inspection of surface bone in skulls of Neanderthal man reveals weathering cracks extensive enough in one specimen, La Chapelle-aux-Saints, to allow preliminary analysis of major patterns of orientation and to make inferences about functional relationships of structures. The fine structure of the bone of the brow ridges is very different from the rest of the skull in the two adults examined, having a peculiar vermiculate surface pattern. Weathering cracks do not appear in this region. This indicates that Neanderthal brow ridges are not closely related to normal mechanical forces such as chewing exertion. It may, however, give further support to theories of Neanderthal brow ridges as protection for the eyes. The localized structure of bone often differs from region to region, and offers new possibilities for the analysis of both contemporary and fossil forms.     

Three major mesoplanktonic communities resolved by in situ imaging in the upper 500 m of the global ocean

Aim

The distribution of mesoplankton communities has been poorly studied at global scale, especially from in situ instruments. This study aims to (1) describe the global distribution of mesoplankton communities in relation to their environment and (2) assess the ability of various environmental-based ocean regionalizations to explain the distribution of these communities.

Location

Global ocean, 0–500 m depth.

Time Period

2008–2019.

Major Taxa Studied

Twenty-eight groups of large mesoplanktonic and macroplanktonic organisms, covering Metazoa, Rhizaria and Cyanobacteria.

Methods

From a global data set of 2500 vertical profiles making use of the Underwater Vision Profiler 5 (UVP5), an in situ imaging instrument, we studied the global distribution of large (>600 μm) mesoplanktonic organisms. Among the 6.8 million imaged objects, 330,000 were large zooplanktonic organisms and phytoplankton colonies, the rest consisting of marine snow particles. Multivariate ordination (PCA) and clustering were used to describe patterns in community composition, while comparison with existing regionalizations was performed with regression methods (RDA).

Results

Within the observed size range, epipelagic plankton communities were Trichodesmium-enriched in the intertropical Atlantic, Copepoda-enriched at high latitudes and in upwelling areas, and Rhizaria-enriched in oligotrophic areas. In the mesopelagic layer, Copepoda-enriched communities were also found at high latitudes and in the Atlantic Ocean, while Rhizaria-enriched communities prevailed in the Peruvian upwelling system and a few mixed communities were found elsewhere. The comparison between the distribution of these communities and a set of existing regionalizations of the ocean suggested that the structure of plankton communities described above is mostly driven by basin-level environmental conditions.

Main Conclusions

In both layers, three types of plankton communities emerged and seemed to be mostly driven by regional environmental conditions. This work sheds light on the role not only of metazoans, but also of unexpected large protists and cyanobacteria in structuring large mesoplankton communities.     

Reduction in animal abundance and oxygen availability during and after the end-Triassic mass extinction

The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η² = 0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η² = 0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.     

Scanning and transmission electron microscopy of the squamose gill-filament epithelium from fresh- and seawater adaptedTilapia

Synopsis The architecture of the gill structure of variousTilapia species was studied in relation to their adaptability to hypersaline media. Using SEM and EM, it was shown that the squamose epithelial cells of the gills have species-typical patterns of ridges on their outer surfaces. These have previously been misinterpreted by other authors as microvilli or stereocillia. The ridges are more dense and better developed in euryhaline species, likeT. zillii, and less so in stenohaline species likeSarotherodon niloticus. Comparing freshwater and seawater-adapted individuals ofT. zillii, S. niloticus, S. galflaeus, andTristramella sacra, it was shown that in fresh water the surface cells are slightly swollen, extending over the openings of the chloride cells. During adaptation to sea water, these ridges become higher and denser and the cell surface shrinks, exposing the underlying orifices of the apical crypts of the chloride cells. The more euryhaline the species, the less change there is in the ridge pattern of the cells during passage from fresh to sea water. This evidence implicates the gill epithelium, together with the chloride cells, in the process of osmoregulation.     

Long-Term m5C Methylome Dynamics Parallel Phenotypic Adaptation in the Cyanobacterium Trichodesmium

A major challenge in modern biology is understanding how the effects of short-term biological responses influence long-term evolutionary adaptation, defined as a genetically determined increase in fitness to novel environments. This is particularly important in globally important microbes experiencing rapid global change, due to their influence on food webs, biogeochemical cycles, and climate. Epigenetic modifications like methylation have been demonstrated to influence short-term plastic responses, which ultimately impact long-term adaptive responses to environmental change. However, there remains a paucity of empirical research examining long-term methylation dynamics during environmental adaptation in nonmodel, ecologically important microbes. Here, we show the first empirical evidence in a marine prokaryote for long-term m5C methylome modifications correlated with phenotypic adaptation to CO₂, using a 7-year evolution experiment (1,000+ generations) with the biogeochemically important marine cyanobacterium Trichodesmium. We identify m5C methylated sites that rapidly changed in response to high (750 µatm) CO₂ exposure and were maintained for at least 4.5 years of CO₂ selection. After 7 years of CO₂ selection, however, m5C methylation levels that initially responded to high-CO₂ returned to ancestral, ambient CO₂ levels. Concurrently, high-CO₂ adapted growth and N₂ fixation rates remained significantly higher than those of ambient CO₂ adapted cell lines irrespective of CO₂ concentration, a trend consistent with genetic assimilation theory. These data demonstrate the maintenance of CO₂-responsive m5C methylation for 4.5 years alongside phenotypic adaptation before returning to ancestral methylation levels. These observations in a globally distributed marine prokaryote provide critical evolutionary insights into biogeochemically important traits under global change.     

Effects of global change on key processes of primary production in marine ecosystems

工业革命以来, 不断加剧的人类活动所引起的大气CO₂浓度增加、温度上升等全球变化问题, 正使得海洋生态系统面临着前所未有的压力。该文通过文献计量的方法分析了国内外的研究现状, 简要地回顾了全球变化对海洋生态系统影响研究的发展简史, 并聚焦海洋暖化、海洋酸化和富营养化与缺氧这三个核心研究方向, 重点阐述了它们对海洋生态系统初级生产的关键过程的影响, 总结了已取得的重要进展以及存在的主要问题, 最后提出前沿展望。     

Combined effects of CO2 and light on large and small isolates of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii from the western tropical Atlantic Ocean

We examined the combined effects of light and pCO₂ on growth, CO₂-fixation and N₂-fixation rates by strains of the unicellular marine N₂-fixing cyanobacterium Crocosphaera watsonii with small (WH0401) and large (WH0402) cells that were isolated from the western tropical Atlantic Ocean. In low-pCO₂-acclimated cultures (190 ppm) of WH0401, growth, CO₂-fixation and N₂-fixation rates were significantly lower than those in cultures acclimated to higher (present-day ～385 ppm, or future ～750 ppm) pCO₂ treatments. Growth rates were not significantly different, however, in low-pCO₂-acclimated cultures of WH0402 in comparison with higher pCO₂ treatments. Unlike previous reports for C. watsonii (strain WH8501), N₂-fixation rates did not increase further in cultures of WH0401 or WH0402 when acclimated to 750 ppm relative to those maintained at present-day pCO₂. Both light and pCO₂ had a significant negative effect on gross : net N₂-fixation rates in WH0402 and trends were similar in WH0401, implying that retention of fixed N was enhanced under elevated light and pCO₂. These data, along with previously reported results, suggest that C. watsonii may have wide-ranging, strain-specific responses to changing light and pCO₂, emphasizing the need for examining the effects of global change on a range of isolates within this biogeochemically important genus. In general, however, our data suggest that cellular N retention and CO₂-fixation rates of C. watsonii may be positively affected by elevated light and pCO₂ within the next 100 years, potentially increasing trophic transfer efficiency of C and N and thereby facilitating uptake of atmospheric carbon by the marine biota.     

Sedimentation of ballasted cells‐free EPS in meromictic Fayetteville Green Lake

Fayetteville Green Lake (FGL) is a recognized, extensively studied present‐day model of the stratified Proterozoic ocean. Nonetheless, biomass sedimentation in FGL remains hard to explain: while virtually all sediment pigments belong to photosynthetic sulfur bacteria from a chemocline, the isotopic carbon signature of the bulk organic matter suggests its epilimnetic phytoplankton origin. To explain the epilimnetic origin of sedimented carbon, we studied the dominant Synechococci, isolated from FGL. Here, we present experimental evidence that FGL Synechococci produce copious extracellular polysaccharides (EPS) especially when availability of inorganic carbon (C_i) is high relative to availability of other macronutrients, for example phosphorus. The accumulating EPS become impregnated with calcium, magnesium, and sodium cations and are released to the environment as ballasted cell coverings. Sedimentation of these cell‐free EPS can constitute the bulk of pigment‐free organic material in FGL sediment. Because increased availability of C_i specifically stimulates production of EPS and the accumulated EPS adsorb cations and become ballasted, we propose the universal role of cyanobacterial EPS in biomass sedimentation in the high‐C_i Paleoproterozoic ocean as well as in modern aquatic systems like FGL.     

Microbial tropicalization driven by a strengthening western ocean boundary current

Western boundary currents (WBCs) redistribute heat and oligotrophic seawater from the tropics to temperate latitudes, with several displaying substantial climate change‐driven intensification over the last century. Strengthening WBCs have been implicated in the poleward range expansion of marine macroflora and fauna, however, the impacts on the structure and function of temperate microbial communities are largely unknown. Here we show that the major subtropical WBC of the South Pacific Ocean, the East Australian Current (EAC), transports microbial assemblages that maintain tropical and oligotrophic (k‐strategist) signatures, to seasonally displace more copiotrophic (r‐strategist) temperate microbial populations within temperate latitudes of the Tasman Sea. We identified specific characteristics of EAC microbial assemblages compared with non‐EAC assemblages, including strain transitions within the SAR11 clade, enrichment of Prochlorococcus, predicted smaller genome sizes and shifts in the importance of several functional genes, including those associated with cyanobacterial photosynthesis, secondary metabolism and fatty acid and lipid transport. At a temperate time‐series site in the Tasman Sea, we observed significant reductions in standing stocks of total carbon and chlorophyll a, and a shift towards smaller phytoplankton and carnivorous copepods, associated with the seasonal impact of the EAC microbial assemblage. In light of the substantial shifts in microbial assemblage structure and function associated with the EAC, we conclude that climate‐driven expansions of WBCs will expand the range of tropical oligotrophic microbes, and potentially profoundly impact the trophic status of temperate waters.     

Defining CO2 and O2 syndromes of marine biomes in the Anthropocene

Research efforts have intensified to foresee the prospects for marine biomes under climate change and anthropogenic drivers over varying temporal and spatial scales. Parallel with these efforts is the utilization of terminology, such as ‘ocean acidification’ (OA) and ‘ocean deoxygenation’ (OD), that can foster rapid comprehension of complex processes driving carbon dioxide (CO₂) and oxygen (O₂) concentrations in the global ocean and thus, are now widely used in discussions within and beyond academia. However, common usage of the terms ‘acidification’ and ‘deoxygenation’ alone are subjective and, without adequate contextualization, have the potential to mislead inferences over drivers that may ultimately shape the future state of marine ecosystems. Here we clarify the usage of the terms OA and OD as global, climate change‐driven processes and discuss the various attributes of elevated CO₂ and reduced O₂ syndromes common to coastal ecosystems. We support the use of the existing terms ‘coastal acidification’ and ‘coastal deoxygenation’ because they help differentiate the sometimes rapid and extreme nature of CO₂ and O₂ syndromes in coastal ecosystems from the global, climate change‐driven processes of OA and OD. Given the complexity and breadth of the processes involved in altering CO₂ and O₂ concentrations across marine ecosystems, we provide a workflow to enable contextualization and clarification of the usage of existing terms and highlight the close link between these two gases across spatial and temporal scales in the ocean. These distinctions are crucial to guide effective communication of research within the scientific community and guide policymakers responsible for intervening on the drivers to secure desirable future ocean states.