Trace Element Concentrations Associated with Mid-Paleozoic Microfossils as Biosignatures to Aid in the Search for Life.

Identifying microbial fossils in the rock record is a difficult task because they are often simple in morphology and can be mimicked by non-biological structures. Biosignatures are essential for identifying putative fossils as being definitively biological in origin, but are often lacking due to geologic effects which can obscure or erase such signs. As such, there is a need for robust biosignature identification techniques. Here we show new evidence for the application of trace elements as biosignatures in microfossils. We found elevated concentrations of magnesium, aluminum, manganese, iron, and strontium colocalized with carbon and sulfur in microfossils from Drummond Basin, a mid-Paleozoic hot spring deposit in Australia. Our results also suggest that trace element sequestrations from modern hot spring deposits persist through substantial host rock alteration. Because some of the oldest fossils on Earth are found in hot spring deposits and ancient hot spring deposits are also thought to occur on Mars, this biosignature technique may be utilized as a valuable tool to aid in the search for extraterrestrial life.

A statistical model of secondary ion emission and attenuation clarifies disparities in quasi-simultaneous arrival coefficients measured with secondary ion mass spectrometry.

RATIONALE: Secondary ion mass spectrometry data collected using electron multiplier detectors are subject to a correction for the quasi-simultaneous arrival (QSA) effect. Published Poisson statistical models indicate that the QSA coefficients, ß, should have an invariant value of 0.5, whereas, with one exception, published experimental determinations vary between 0.6 and 1.0, with a mean value of 0.75. METHODS: We developed a more complex model, combining both ion emission and attenuation, that predicts the observed range in measured ß and elucidates the mechanism of secondary ion formation. For a given aperture setting, any secondary ion has an equal probability of successful transit to the electron multiplier. Binomial statistics can model pass-fail aperture attenuation but require probability distributions of the quasi-simultaneously emitted (QSE) ion tally, per primary ion, as input. Assuming (a) that each primary ion impact results in 0, 1, 2,… secondary ion emissions, randomly, with an average Ks and (b) that there is finite probability (P2) of a further emission process dependent on Ks , the required QSE probability distributions were generated via a combined Poisson-binomial statistical model. RESULTS: The value of ß was output as a function of Ks and P2. For values of P2 > 0 and any value of Ks , ß always exceeds 0.5. As P2 → 0, ß â†’ 0.5; for values of increasing P2 > 0.5 and decreasing Ks < 0.5, ß â†’ >1. CONCLUSIONS: Were the emission of one ion not to influence the probability of the formation of a second (i.e. model output for P2 = 0), ß should always be 0.5. Yet measurements have never reported this value. Consequently, assuming that published ß values are correct, emissions of QSE secondary ions do not occur independently, and it may be inferred that there are linked mechanisms of secondary ion formation as shown here.

Trace Element Concentrations in Hydrothermal Silica Deposits as a Potential Biosignature.

Uncovering and understanding the chemical and fossil record of ancient life is crucial to understanding how life arose, evolved, and distributed itself across Earth. Potential signs of ancient life, however, are often challenging to establish as definitively biological and require multiple lines of evidence. Hydrothermal silica deposits may preserve some of the most ancient evidence of life on Earth, and such deposits are also suggested to exist on the surface of Mars. Here we use micron-scale elemental mapping by secondary ion mass spectrometry to explore for trace elements that are preferentially sequestered by microbial life and subsequently preserved in hydrothermal deposits. The spatial distributions and concentrations of trace elements associated with life in such hydrothermal silica deposits may have a novel application as a biosignature in constraining ancient life on Earth as well as the search for evidence of past life on Mars. We find that active microbial mats and recent siliceous sinter deposits from an alkaline hot spring in Yellowstone National Park appear to sequester and preserve Ga, Fe, and perhaps Mn through early diagenesis as indicators of the presence of life during formation.

Phototrophic extracellular electron uptake is linked to carbon dioxide fixation in the bacterium Rhodopseudomonas palustris.

Extracellular electron uptake (EEU) is the ability of microbes to take up electrons from solid-phase conductive substances such as metal oxides. EEU is performed by prevalent phototrophic bacterial genera, but the electron transfer pathways and the physiological electron sinks are poorly understood. Here we show that electrons enter the photosynthetic electron transport chain during EEU in the phototrophic bacterium Rhodopseudomonas palustris TIE-1. Cathodic electron flow is also correlated with a highly reducing intracellular redox environment. We show that reducing equivalents are used for carbon dioxide (CO2) fixation, which is the primary electron sink. Deletion of the genes encoding ruBisCO (the CO2-fixing enzyme of the Calvin-Benson-Bassham cycle) leads to a 90% reduction in EEU. This work shows that phototrophs can directly use solid-phase conductive substances for electron transfer, energy transduction, and CO2 fixation.

Sulfur isotope analysis of microcrystalline iron sulfides using secondary ion mass spectrometry imaging: Extracting local paleo-environmental information from modern and ancient sediments.

RATIONALE: Sulfur isotope ratio measurements of bulk sulfide from marine sediments have often been used to reconstruct environmental conditions associated with their formation. In situ microscale spot analyses by secondary ion mass spectrometry (SIMS) and laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) have been utilized for the same purpose. However, these techniques are often not suitable for studying small (≤10 µm) grains or for detecting intra-grain variability. METHODS: Here, we present a method for the physical extraction (using lithium polytungstate heavy liquid) and subsequent sulfur isotope analysis (using SIMS; CAMECA IMS 7f-GEO) of microcrystalline iron sulfides. SIMS sulfur isotope ratio measurements were made via Cs+ bombardment of raster squares with sides of 20-130 µm, using an electron multiplier (EM) detector to collect counts of 32 S- and 34 S- for each pixel (128 × 128 pixel grids) for between 20 and 960 cycles. RESULTS: The extraction procedure did not discernibly alter pyrite grain-size distributions. The apparent inter-grain variability in 34 S/32 S in 1-4 µm-sized pyrite and marcasite fragments from isotopically homogeneous hydrothermal crystals was ~ ±2‰ (1σ), comparable with the standard error of the mean for individual measurements (≤ ±2‰, 1σ). In contrast, grain-specific 34 S/32 S ratios in modern and ancient sedimentary pyrites and marcasites can have inter- and intra-grain variability >60‰. The distributions of intra-sample isotopic variability are consistent with bulk 34 S/32 S values. CONCLUSIONS: SIMS analyses of isolated iron sulfide grains yielded distributions that are isotopically representative of bulk 34 S/32 S values. Populations of iron sulfide grains from sedimentary samples record the evolution of the S-isotopic composition of pore water sulfide in their S-isotopic compositions. These data allow past local environmental conditions to be inferred.

Boom-bust dynamics in biological invasions: towards an improved application of the concept.

Boom-bust dynamics - the rise of a population to outbreak levels, followed by a dramatic decline - have been associated with biological invasions and offered as a reason not to manage troublesome invaders. However, boom-bust dynamics rarely have been critically defined, analyzed, or interpreted. Here, we define boom-bust dynamics and provide specific suggestions for improving the application of the boom-bust concept. Boom-bust dynamics can arise from many causes, some closely associated with invasions, but others occurring across a wide range of ecological settings, especially when environmental conditions are changing rapidly. As a result, it is difficult to infer cause or predict future trajectories merely by observing the dynamic. We use tests with simulated data to show that a common metric for detecting and describing boom-bust dynamics, decline from an observed peak to a subsequent trough, tends to severely overestimate the frequency and severity of busts, and should be used cautiously if at all. We review and test other metrics that are better suited to describe boom-bust dynamics. Understanding the frequency and importance of boom-bust dynamics requires empirical studies of large, representative, long-term data sets that use clear definitions of boom-bust, appropriate analytical methods, and careful interpretations.

Investigation of the quasi-simultaneous arrival (QSA) effect on a CAMECA IMS 7f-GEO.

RATIONALE: IMS 7f-GEO isotope ratio applications increasingly involve analyses (e.g., S- or O- isotopes, coupled with primary ion currents <30 pA) for which quasi-simultaneous arrival (QSA) could compromise precision and accuracy of data. QSA and associated correction have been widely investigated for the CAMECA NanoSIMS instruments, but not for the IMS series. METHODS: Sulfur and oxygen isotopic ratio experiments were performed using an electron multiplier (EM) detector, employing Cs+ primary ion currents of 1, 2, 5 and 11.5 pA (nominal) and a variety of secondary ion transmissions to vary QSA probability. An experiment to distinguish between QSA undercounting and purported aperture-related mass fractionation was performed using an EM for 16 O- and 18 O- plus an additional 16 O- measurement using a Faraday cup (FC) detector. An experiment to investigate the accuracy of the QSA correction was performed by comparing S isotopic ratios obtained using an EM with those obtained on the same sample using dual FCs. RESULTS: The QSA effect was observed on the IMS-7f-GEO, and QSA coefficients (ß) of ~0.66 were determined, in agreement with reported NanoSIMS measurements, but different from the value (0.5) predicted using Poisson statistics. Aperture-related fractionation was not sufficient to explain the difference but uncertainties in primary ion flux measurement could play a role. When QSA corrected, the isotope ratio data obtained using the EM agreed with the dual FC data, within statistical error. CONCLUSIONS: QSA undercounting could compromise isotope ratio analyses requiring ~1 × 105 counts per second for the major isotope and primary currents <20 pA. The error could be >8‰ for a 1 pA primary current. However, correction can be accurately applied. For instrumental mass fractionation (IMF)-corrected data, the magnitude of the error resulting from not correcting for QSA is dependent on the difference in secondary ion count rate between the unknown and standard analyses. Copyright © 2017 John Wiley & Sons, Ltd.

Oceanographic Currents and Local Ecological Knowledge Indicate, and Genetics Does Not Refute, a Contemporary Pattern of Larval Dispersal for The Ornate Spiny Lobster, Panulirus ornatus in the South-East Asian Archipelago.

Here we utilize a combination of genetic data, oceanographic data, and local ecological knowledge to assess connectivity patterns of the ornate spiny lobster Panulirus ornatus (Fabricius, 1798) in the South-East Asian archipelago from Vietnam to Australia. Partial mitochondrial DNA control region and 10 polymorphic microsatellites did not detect genetic structure of 216 wild P. ornatus samples from Australia, Indonesia and Vietnam. Analyses show no evidence for genetic differentiation among populations (mtDNA control region sequences ΦST = -0.008; microsatellite loci FST = 0.003). A lack of evidence for regional or localized mtDNA haplotype clusters, or geographic clusters of microsatellite genotypes, reveals a pattern of high gene flow in P. ornatus throughout the South-East Asian Archipelago. This lack of genetic structure may be due to the oceanography-driven connectivity of the pelagic lobster larvae between spawning grounds in Papua New Guinea, the Philippines and, possibly, Indonesia. The connectivity cycle necessitates three generations. The lack of genetic structure of P. ornatus population in the South-East Asian archipelago has important implications for the sustainable management of this lobster in that the species within the region needs to be managed as one genetic stock.

Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea).

Rates of biodiversity loss are higher in freshwater ecosystems than in most terrestrial or marine ecosystems, making freshwater conservation a priority. However, prioritization methods are impeded by insufficient knowledge on the distribution and conservation status of freshwater taxa, particularly invertebrates. We evaluated the extinction risk of the world's 590 freshwater crayfish species using the IUCN Categories and Criteria and found 32% of all species are threatened with extinction. The level of extinction risk differed between families, with proportionally more threatened species in the Parastacidae and Astacidae than in the Cambaridae. Four described species were Extinct and 21% were assessed as Data Deficient. There was geographical variation in the dominant threats affecting the main centres of crayfish diversity. The majority of threatened US and Mexican species face threats associated with urban development, pollution, damming and water management. Conversely, the majority of Australian threatened species are affected by climate change, harvesting, agriculture and invasive species. Only a small proportion of crayfish are found within the boundaries of protected areas, suggesting that alternative means of long-term protection will be required. Our study highlights many of the significant challenges yet to come for freshwater biodiversity unless conservation planning shifts from a reactive to proactive approach.

Public broadcasting, media engagement, and 2-1-1: using mass communication to increase the use of social services.

BACKGROUND: The 2008-2009 subprime mortgage crisis was catastrophic, not only for the global economy but for families across the social spectrum. The resultant economic upheaval threatened the livelihoods, well-being, and health of many citizens, who were often unsure where to turn for help. At this critical juncture, public broadcasting stations worked to connect viewers to support resources through 2-1-1. PURPOSE: This study was designed to evaluate the ability of public broadcasting to increase the use of information and referral services. METHODS: Autoregressive integrated moving average (ARIMA) modeling and regression analysis document the relationship between public broadcasting initiatives and 2-1-1 call volume in 35 highly affected U.S. markets. Time-series data from St. Louis MO were collected and analyzed in 2008. Station-level data from across the nation were collected during 2009-2010 and analyzed in 2010. RESULTS: ARIMA results show a distinct linkage between the timing and duration of Channel 9 in St. Louis MO (KETC) programming and a subsequent (approximately 400%) increase in 2-1-1 calls regarding financial services and assistance. Regression path analysis not only found evidence of this same effect nationally but also showed that differences in the broadcaster's orientation and approach mediated effects. Specifically, stations' orientations toward engagement were mediated through strong outreach strategies to increase 2-1-1 use. CONCLUSIONS: This study documents the ability of public broadcasting to help citizens in need connect with social resources through 2-1-1 services. By focusing attention on the mortgage crisis and its attendant consequences, and by publicizing 2-1-1 services as a gateway to supportive resources, public broadcasters fostered linkages between those in need and social resources. Moreover, the level of a station's commitment to engaging citizens had a strong bearing on the success of its programming initiatives and community partnerships with organizations such as 2-1-1.

Quantifying a dynamic risk landscape: heterogeneous predator activity and implications for prey persistence.

Spatial heterogeneity in predation risk can ameliorate impacts on prey populations, particularly for prey of generalists. Spatially heterogeneous risk implies the existence of refugia, and the spatial scale of those refugia and their persistence over time affect whether prey can avoid predation by aggregating therein. Our objective was to quantify the magnitude, spatial scale, and temporal persistence of heterogeneity in risk of predation by white-footed mice (Peromyscus leucopus), an abundant generalist predator of gypsy moths (Lymantria dispar) and songbirds. We used track plates to measure white-footed mouse activity at > 170 trees in each of three forest plots in upstate New York during summers of 2003-2005. We quantified the mean and coefficient of variation of track activity among trees by fitting the beta-binomial distribution to data from each plot and study period. We measured temporal persistence by disattenuated autocorrelation, and spatial scale by fitting exponential variograms. Mice were much less abundant in 2005 than the other two years, leading to lower overall track activity but higher coefficient of variation among trees. Mouse track activity at individual trees was positively autocorrelated between monthly study periods in 2003 and 2004, and even between the two years, whereas temporal autocorrelation in 2005 was much weaker. Track activity showed positive spatial autocorrelation over lag distances from approximately 30 to > 1000 m. These findings indicate that mouse activity, and hence risk to their prey, varies substantially in space at spatial and temporal scales that appear responsive to mouse population dynamics. The spatial scale and temporal persistence of that variation imply that prey may benefit from returning to, or failing to disperse from, refugia.

A Darwinian view of metabolism: molecular properties determine fitness.

Why do organisms make the types of chemicals that they do? Evolutionary theory tells us that individuals within populations will be subject to mutation and that some of those mutations will be enzyme variants that make new chemicals. A mutant making a novel chemical for that species will only survive in the population if the 'cost' of making the new chemical is outweighed by the benefits that result from making that molecule. The benefits, or adverse consequences, that a novel chemical X can confer to the individual organism are not a property of the simple existence of X in the cell but can be traced to one of the multiple properties that X will possess because of its molecular structure. By considering only three basic types of molecular property and by considering how selection pressures will differ for each kind of property, it is possible to account for much of the chemical diversity made by organisms. Such an evolutionary model can also explain why the properties of enzymes will differ depending on the molecular properties of the chemicals they make, and why the widely accepted terms 'primary metabolism' and 'secondary metabolism' have been so misleading and unsatisfactory.

Leaf- and shoot-level plasticity in response to different nutrient and water availabilities.

Phenotypic plasticity in response to environmental variation occurs at all levels of organization and across temporal scales within plants. However, the magnitude and functional significance of plasticity is largely unexplored in perennial species. We measured the plasticity of leaf- and shoot-level physiological, morphological and developmental traits in nursery-grown Populus deltoides Bartr. ex Marsh. individuals subjected to different nutrient and water availabilities. We also examined the extent to which nutrient and water availability influenced the relationships between these traits and productivity. Populus deltoides responded to changes in resource availability with high plasticity in shoot-level traits and moderate plasticity in leaf-level traits. Although shoot-level traits generally correlated strongly with productivity across fertilization and irrigation treatments, few leaf-level traits correlated with productivity, and the relationships depended on the resource examined. In fertilized plants, leaf nitrogen concentration was negatively correlated with productivity, suggesting that growth, rather than enhanced leaf quality, is an important response to fertilization in this species. With the exception of photosynthetic nitrogen-use efficiency, traits associated with resource conservation (leaf senescence rate, water-use efficiency and leaf mass per area) were uncorrelated with short-term productivity in nutrient- and water-stressed plants. Our results suggest that plasticity in shoot-level growth traits has a greater impact on plant productivity than does plasticity in leaf-level traits and that the relationships between traits and productivity are highly resource dependent.

Spatial selection and inheritance: applying evolutionary concepts to population dynamics in heterogeneous space.

Organisms in highly suitable sites generally produce more offspring, and offspring can inherit this suitability by not dispersing far. This combination of spatial selection and spatial inheritance acts to bias the distribution of organisms toward suitable sites and thereby increase mean fitness (i.e., per capita population increase). Thus, population growth rates in heterogeneous space change over time by a process conceptually analogous to evolution by natural selection, opening avenues for theoretical cross-pollination between evolutionary biology and ecology. We operationally define spatial inheritance and spatial selective differential and then combine these two factors in a modification of the breeder's equation, derived from simple models of population growth in heterogeneous space. The modified breeder's equation yields a conservative criterion for persistence in hostile environments estimable from field measurements. We apply this framework for understanding gypsy moth population persistence amidst abundant predators and find that the predictions of the modified breeder's equation match initial changes in population growth rate in independent simulation output. The analogy between spatial dynamics and natural selection conceptually links ecology and evolution, provides a spatially implicit framework for modeling spatial population dynamics, and represents an important null model for studying habitat selection.

Ecosystem engineering in space and time.

The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than 10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism--engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences.

Variation in Eastern cottonwood (Populus deltoides Bartr.) phloem sap content caused by leaf development may affect feeding site selection behavior of the aphid, Chaitophorous populicola Thomas (Homoptera: Aphididae).

Apterous populations of Chaitophorous populicola Thomas (Homoptera: Aphididae) appear to track Eastern cottonwood (Populus deltoides Bartr.) leaf development. Few aphids occur on mature leaves. Marked individual aphids on leaves of different developmental stages were observed through a period of new leaf initiation. Nymph and adult C. populicola frequently track leaf development by moving up to younger leaves. A comparison of phloem sap constituents and leaf toughness among leaf developmental stages revealed some differences that could be used by C. populicola to determine leaf age. Phloem sap exudates, collected from P. deltoides leaves of different developmental stages, were analyzed by high-performance liquid chromatography for free amino acids and the phenolic glycoside salicin. Sucrose concentration in exudates, indicative of phloem sap exudation rate, was uniform among leaf stages. Of 20 amino acids examined, only aspartic acid and gamma-amino-n-butyric acid (GABA) concentrations differed significantly between leaf stages. Forward stepwise discriminant function analysis showed that seven of the amino acids analyzed are useful for classifying leaf maturity groupings. Aphid-infested cottonwoods had lower cystine concentrations in phloem sap than aphid-free plants. Salicin concentration was significantly higher in new leaves. Leaf toughness was assessed by lignin density and distance measurements in petiole cross-sections. Rapidly expanding leaves had significantly less lignification and new leaves had shorter distances to the vascular bundles than senescent leaves. These physiological and phytochemical differences among P. deltoides leaf developmental stages may contribute to the leaf stage selection patterns exhibited by the aphid, C. populicola.

Using ecosystem engineers to restore ecological systems.

Ecosystem engineers affect other organisms by creating, modifying, maintaining or destroying habitats. Despite widespread recognition of these often important effects, the ecosystem engineering concept has yet to be widely used in ecological applications. Here, we present a conceptual framework that shows how consideration of ecosystem engineers can be used to assess the likelihood of restoration of a system to a desired state, the type of changes necessary for successful restoration and how restoration efforts can be most effectively partitioned between direct human intervention and natural ecosystem engineers.

Physiological and developmental effects of O3 on cottonwood growth in urban and rural sites.

Previously we found that cloned cottonwood saplings (Populus deltoides) grew twice as large in New York, New York, USA, compared to surrounding rural environments and that soils, temperature, CO2, nutrient deposition, and microclimatic variables could not account for the greater urban plant biomass. Correlations between final season biomass and cumulative O3 exposures, combined with twofold growth reductions in an open-top chamber experiment provided strong evidence that higher cumulative O3 exposures in rural sites reduced growth in the country. Here, we assess the field gas exchange, growth and development, and allocation responses underlying the observed growth differences and compare them with isolated O3 responses documented in the open-top chamber experiment. Cottonwoods showed no visible foliar injury, reduced photosynthesis of recently expanded foliage, early leaf senescence, protective reduction in stomatal conductance, or compensatory allocation to shoot relative to root biomass for either the chamber or field experiment. Instead, O3-impacted chamber plants had significantly higher conductance and reduced photosynthesis of older foliage that led to reduced leaf area production and a twofold biomass reduction in the absence of visible injury. Rural-grown field plants showed the same pattern of significantly higher conductance in the absence of concomitant increases in photosynthesis that was indicative of a loss of stomatal control. Incremental changes in foliar production were also significantly inversely related to fluctuations in ambient O3 exposures. The similarity in biomass, gas exchange, phenological, and allocation responses between chamber and field experiments indicate that mechanisms accounting for reduced growth at rural sites were consistent with those in the open-top chamber O3 experiment. This study shows the limitation of visible symptoms as a sole diagnostic factor for documenting detrimental O3 impacts and points toward a new approach to show O3 impacts when visible injury is not present. Namely, O3-impacted vegetation showed an unusual inverse relationship of increased conductance with lower photosynthesis of older foliage that was indicative of a loss of stomatal control. This increased stomatal conductance of O3-impacted vegetation accentuates pollutant flux into affected foliage and has important implications for system water balance during warm, dry portions of the growing season when O3 concentrations are highest.