Variation of stable silicon isotopes: Analytical developments and applications in Precambrian geochemistry

Die vorliegende Dissertation behandelt die Gesamtgesteinsanalyse stabiler Siliziumisotope mit Hilfe einer „Multi Collector-ICP-MS“. Die Analysen fanden in Kooperation mit dem „Royal Museum for Central Africa“ in Belgien statt. Einer der Schwerpunkte des ersten Kapitels ist die erstmalige Analyse des δ30Si –Wertes an einem konventionellen Nu PlasmaTM „Multi-Collector ICP-MS“ Instrument, durch die Eliminierung der den 30Si “peak” überlagernden 14N16O Interferenz. Die Analyse von δ30Si wurde durch technische Modifikationen der Anlage erreicht, welche eine höherer Massenauflösung ermöglichten. Die sorgsame Charakterisierung eines adäquaten Referenzmaterials ist unabdingbar für die Abschätzung der Genauigkeit einer Messung. Die Bestimmung der „U.S. Geological Survey“ Referenzmaterialien bildet den zweiten Schwerpunkt dieses Kapitales. Die Analyse zweier hawaiianischer Standards (BHVO-1 and BHVO-2), belegt die präzise und genaue δ30Si Bestimmung und bietet Vergleichsdaten als Qualitätskontrolle für andere Labore. Das zweite Kapitel befasst sich mit kombinierter Silizium-/Sauerstoffisotope zur Untersuchung der Entstehung der Silizifizierung vulkanischer Gesteine des „Barberton Greenstone Belt“, Südafrika. Im Gegensatz zu heute, war die Silizifizierung der Oberflächennahen Schichten, einschließlich der „Chert“ Bildung, weitverbreitete Prozesse am präkambrischen Ozeanboden. Diese Horizonte sind Zeugen einer extremen Siliziummobilisierung in der Frühzeit der Erde. Dieses Kapitel behandelt die Analyse von Silizium- und Sauerstoffisotopen an drei unterschiedlichen Gesteinsprofilen mit unterschiedlich stark silizifizierten Basalten und überlagernden geschichteten „Cherts“ der 3.54, 3.45 und 3.33 Mill. Jr. alten Theespruit, Kromberg und Hooggenoeg Formationen. Siliziumisotope, Sauerstoffisotope und die SiO2-Gehalte demonstrieren in allen drei Gesteinsprofilen eine positive Korrelation mit dem Silizifizierungsgrad, jedoch mit unterschiedlichen Steigungen der δ30Si-δ18O-Verhältnisse. Meerwasser wird als Quelle des Siliziums für den Silizifizierungsprozess betrachtet. Berechnungen haben gezeigt, dass eine klassische Wasser-Gestein Wechselwirkung die Siliziumisotopenvariation nicht beeinflussen kann, da die Konzentration von Si im Meerwasser zu gering ist (49 ppm). Die Daten stimmen mit einer Zwei-Endglieder-Komponentenmischung überein, mit Basalt und „Chert“ als jeweilige Endglieder. Unsere gegenwärtigen Daten an den „Cherts“ bestätigen einen Anstieg der Isotopenzusammensetzung über der Zeit. Mögliche Faktoren, die für unterschiedliche Steigungen der δ30Si-δ18O Verhältnisse verantwortlich sein könnten sind Veränderungen in der Meerwasserisotopie, der Wassertemperatur oder sekundäre Alterationseffekte. Das letzte Kapitel beinhaltet potentielle Variationen in der Quellregion archaischer Granitoide: die Si-Isotopen Perspektive. Natriumhaltige Tonalit-Trondhjemit-Granodiorit (TTG) Intrusiva repräsentieren große Anteile der archaischen Kruste. Im Gegensatz dazu ist die heutige Kruste kaliumhaltiger (GMS-Gruppe: Granit-Monzonite-Syenite). Prozesse, die zu dem Wechsel von natriumhaltiger zu kaliumhaltiger Kruste führten sind die Thematik diesen Kapitels. Siliziumisotopenmessungen wurden hier kombiniert mit Haupt- und Spurenelementanalysen an unterschiedlichen Generationen der 3.55 bis 3.10 Mill. Yr. alten TTG und GMS Intrusiva aus dem Arbeitsgebiet. Die δ30Si-Werte in den unterschiedlichen Plutonit Generationen zeigen einen leichten Anstieg der Isotopie mit der Zeit, wobei natriumhaltige Intrusiva die niedrigste Si-Isotopenzusammensetzung aufweisen. Der leichte Anstieg in der Siliziumisotopenzusammensetzung über die Zeit könnte auf unterschiedliche Temperaturbedingungen in der Quellregion der Granitoide hinweisen. Die Entstehung von Na-reichen, leichten d30Si Granitoiden würde demnach bei höheren Temperaturen erfolgen. Die Ähnlichkeit der δ30Si-Werte in archaischen K-reichen Plutoniten und phanerozoischen K-reichen Plutoniten wird ebenfalls deutlich.

Time-resolved surface enhanced resonance Raman spectro-electrochemistry of heme proteins

The membrane protein Cytochrome c Oxidase (CcO) is one of the most important functional bio-molecules. It appears in almost every eukaryotic cell and many bacteria. Although the different species differ in the number of subunits, the functional differences are merely marginal. CcO is the terminal link in the electron transfer pathway of the mitochondrial respiratory chain. Electrons transferred to the catalytic center of the enzyme conduce to the reduction of molecular oxygen to water. Oxygen reduction is coupled to the pumping of protons into the inter-membrane space and hence generates a difference in electrochemical potential of protons across the inner mitochondrial membrane. This potential difference drives the synthesis of adenosine triphosphate (ATP), which is the universal energy carrier within all biological cells. rnrnThe goal of the present work is to contribute to a better understanding of the functional mechanism of CcO by using time-resolved surface enhanced resonance Raman spectroscopy (TR-SERRS). Despite intensive research effort within the last decades, the functional mechanism of CcO is still subject to controversial discussions. It was the primary goal of this dissertation to initiate electron transfer to the redox centers CuA, heme a, heme a3 and CuB electrochemically and to observe the corresponding redox transitions in-situ with a focus on the two heme structures by using SERRS. A measuring cell was developed, which allowed combination of electrochemical excitation with Raman spectroscopy for the purpose of performing the accordant measurements. Cytochrome c was used as a benchmark system to test the new measuring cell and to prove the feasibility of appropriate Raman measurements. In contrast to CcO the heme protein cc contains only a single heme structure. Nevertheless, characteristic Raman bands of the hemes can be observed for both proteins.rnrnIn order to investigate CcO it was immobilized on top of a silver substrate and embedded into an artificial membrane. The catalytic activity of CcO and therefore the complete functional capability of the enzyme within the biomimetic membrane architecture was verified using cyclic voltammetry. Raman spectroscopy was performed using a special nano-structured silver surface, which was developed within the scope of the present work. This new substrate combined two fundamental properties. It facilitated the formation of a protein tethered bilayer lipid membrane (ptBLM) and it allowed obtaining Raman spectra with sufficient high signal-to-noise ratios.rnSpectro-electrochemical investigations showed that at open circuit potential the enzyme exists in a mixed-valence state, with heme a and and heme a3 in the reduced and oxidized state, respectively. This was considered as an intermediate state between the non-activated and the fully activated state of CcO. Time-resolved SERRS measurements revealed that a hampered electron transfer to the redox center heme a3 characterizes this intermediate state.rn

Identification of stock units of Mullus barbatus (Linnaeus, 1758) in the Italian seas: development of genomic 2b-RAD markers and biological variation analysis.

This thesis is settled within the STOCKMAPPING project, which represents one of the studies that were developed in the framework of RITMARE Flagship project. The main goals of STOCKMAPPING were the creation of a genomic mapping for stocks of demersal target species and the assembling of a database of population genomic, in order to identify stocks and stocks boundaries. The thesis focuses on three main objectives representing the core for the initial assessment of the methodologies and structure that would be applied to the entire STOCKMAPPING project: individuation of an analytical design to identify and locate stocks and stocks boundaries of Mullus barbatus, application of a multidisciplinary approach to validate biological methods and an initial assessment and improvement for the genotyping by sequencing technique utilized (2b-RAD). The first step is the individuation of an analytical design that has to take in to account the biological characteristics of red mullet and being representative for STOCKMAPPING commitments. In this framework a reduction and selection steps was needed due to budget reduction. Sampling areas were ranked according the individuation of four priorities. To guarantee a multidisciplinary approach the biological data associated to the collected samples were used to investigate differences between sampling areas and GSAs. Genomic techniques were applied to red mullet for the first time so an initial assessment of molecular protocols for DNA extraction and 2b-RAD processing were needed. At the end 192 good quality DNAs have been extracted and eight samples have been processed with 2b-RAD. Utilizing the software Stacks for sequences analyses a great number of SNPs markers among the eight samples have been identified. Several tests have been performed changing the main parameter of the Stacks pipeline in order to identify the most explicative and functional sets of parameters.

Stock boundaries of Parapenaeus longirostris (Lucas, 1846) populations in the Italian seas: Development of genomic 2b-RAD markers and biological variation analysis.

This thesis is developed in the contest of Ritmare project WP1, which main objective is the development of a sustainable fishery through the identification of populations boundaries in commercially important species in Italian Seas. Three main objectives are discussed in order to help reach the main purpose of identification of stock boundaries in Parapenaeus longirostris: 1 -Development of a representative sampling design for Italian seas; 2 -Evaluation of 2b-RAD protocol; 3 -Investigation of populations through biological data analysis. First of all we defined and accomplished a sampling design which properly represents all Italian seas. Then we used information and data about nursery areas distribution, abundance of populations and importance of P. longirostris in local fishery, to develop an experimental design that prioritize the most important areas to maximize the results with actual project funds. We introduced for the first time the use of 2b-RAD on this species, a genotyping method based on sequencing the uniform fragments produced by type IIB restriction endonucleases. Thanks to this method we were able to move from genetics to the more complex genomics. In order to proceed with 2b-RAD we performed several tests to identify the best DNA extraction kit and protocol and finally we were able to extract 192 high quality DNA extracts ready to be processed. We tested 2b-RAD with five samples and after high-throughput sequencing of libraries we used the software “Stacks” to analyze the sequences. We obtained positive results identifying a great number of SNP markers among the five samples. To guarantee a multidisciplinary approach we used the biological data associated to the collected samples to investigate differences between geographical samples. Such approach assures continuity with other project, for instance STOCKMED, which utilize a combination of molecular and biological analysis as well.

Gespeicherte Ionen in der Paulfalle: Voruntersuchungen zur Lebensdauermessung des metastabilen 6D-3/2-Zustands des 226 Ra +, Speichereigenschaften von 138 Ba + und 28 N 2 + bei Variation des Puffergasdrucks

Auf Paulfallen basierende Experimente spielen eine wichtige Rolle in verschiedenen Bereichen der Physik, z.B. der Atomphysik zum Test theoretischer Modelle und der Massenspektroskopie. Die vorliegende Arbeit widmet sich beiden Themengebieten und gliedert sich entsprechend in zwei Teilbereiche: 1) Erdalkali-Ionen sind aufgrund ihrer Energieniveaus optimale Kandidaten für Laserspektroskopie-Experimente mit Ionenfallen und bestens geeignet, um mittels der spektroskopischen Daten die theoretischen Modelle zu testen. Lediglich für Ra+ fehlen bislang als einzigem Erdalkali-Ion diese Daten wie z.B. die Lebensdauern der metastabilen Niveaus. Diese wären auch von Interesse für bereits geplante Radium-Experimente zur Paritätsverletzung. Im ersten Teil dieser Arbeit wird der Aufbau eines Laser-Paulfallenexperiments zur Messung der Lebensdauer des 6D3/2 Zustands von 226Ra+ dokumentiert und es werden Testmessungen mit 138Ba+ vorgestellt. 2) Für die Verwendung der Paulfalle in der Massenspektroskopie und zur Analyse von Reaktionsprodukten ist die Kenntnis der Lage der im Speicherbereich auftretenden nichtlinearen Resonanzen wesentlich, ebenso wie deren Veränderung durch Dämpfung und Raumladung. Im zweiten Teil dieser Arbeit werden detaillierte Untersuchungen der Speicherung großer puffergasgekühlter Ionenwolken an zwei unterschiedlichen Paulfallen-Experimenten vorgestellt. Am ersten wurden 138Ba+-Ionenwolken kontinuierlich durch Laserspektroskopie bzw. über einen elektronischen Nachweis beobachtet, während das zweite N2+-Molekülionen automatisiert destruktiv nachwies. Am N2+-Experiment wurden zwei hochaufgelöste Messungen des ersten Speicherbereichs durchgeführt, die erstmals eine direkte Überprüfung der theoretisch berechneten Verläufe der Resonanzen mit experimentellen Daten erlauben. Die Nachweiseichung ermöglichte dabei zum ersten Mal die Angabe absoluter Ionenzahlen. Im Gegensatz zu vergleichbaren früheren Messungen wurden hierbei die sich überlagernden Speicherbereiche von 4 simultan gespeicherten Ionensorten beobachtet und zur Analyse der Resonanzen herangezogen. Die nichtlinearen Resonanzen wurden untersucht bei Variation von Puffergasdruck und Ionenzahl, wobei kollektive Resonanzen ohne zusätzliche externe Anregung beobachtet wurden. Die gemessenen Raumladungsverschiebungen wurden mit theoretischen Modellen verglichen. Bei Variation des Puffergasdrucks wurde mit Bariumionen die räumliche Ausdehnung der Ionenwolke gemessen und mit Stickstoffionen die Verschiebung des Punktes optimaler Speicherung bestimmt. Dabei wurde festgestellt, daß der zum Ioneneinfang optimale Puffergasdruck kleiner ist als der, bei dem die längsten Speicherdauern erzielt werden. Mit gespeicherten N2+-Ionen wurde die Position extern angeregter kollektiver und individueller Resonanzen im Frequenzspektrum bei Änderung der Parameter Ionenzahl, Puffergasdruck und Dauer der Anregung untersucht, ebenso wie die Resonanzform, die mit theoretischen Linienformen verglichen wurde. Bei Änderung der Fallenparameter wurden verstärkende Effekte zwischen nahen kollektiven Resonanzen festgestellt. Die Beobachtung, welche der im Frequenzspektrum vorher identifizierten Bewegungs-Resonanzen sich bei Variation der Fallenparameter a bzw. q überlagern, ermöglicht eine bislang nicht beschriebene einfache Methode der Bestimmung von nichtlinearen Resonanzen im Stabilitätsdiagramm.

Temporal variation of genetic diversity and differentiation of albacore, Thunnus alalunga, in the Mediterranean Sea

This study is on albacore (Thunnus alalunga, Bonnaterre 1788), an epi- and mesopelagic oceanic tuna species cosmopolitan in the tropical and temperate waters of all oceans including the Mediterranean Sea, extending in a broad band between 40°N and 40°S. What it’s known about albacore population structure is based on different studies that used fisheries data, RFLP, mtDNA control region and nuDNA markers, blood lectins analysis, individual tags and microsatellite. At the moment, for T. alalunga six management units are recognized: the North Pacific, South Pacific, Indian, North Atlantic, South Atlantic and Mediterranean stocks. In this study I have done a temporal and spatial comparison of genetic variability between different Mediterranean populations of Thunnus alalunga matching an historical dataset ca. from 1920s composed of 43 individuals divided in 3 populations (NADR, SPAIN and CMED) with a modern dataset composed of 254 individuals and 7 populations (BAL, CYP, LIG, TYR, TUR, ADR, ALB). The investigation was possible using a panel of 94 nuclear SNPs, built specifically for the target species at the University of Basque Country UPV/EHU. First analysis done was the Hardy-Weinberg, then the number of clusters (K) was determined using STRUCTURE and to assess the genetic variability, allele frequencies, the average number of alleles per locus, expected (He) and observed (Ho) heterozygosis, and the index of polymorphism (P) was used the software Genetix. Historical and modern samples gives different results, showing a clear loss of genetic diversity over time leading to a single cluster in modern albacore instead of the two found in historical samples. What this study reveals is very important for conservation concerns, and additional research endeavours are needed.

Seasonality and diel variation in blue whale D calls recorded in the Southern California Bight

Passive acoustic data have been collected using HARPs (High-frequency Acoustic Recording Packages) and were used to assess (1) the seasonality of blue whale D calls in the Southern California Bight, (2) their interannual abundance during 2007-2012 and (3) their diel variation. This goal has been achieved running the GPL (Generalized Power-Law) automated detector. (1) Blue whale D calls were detected in the Southern California Bight from May through November with a peak in July, even though few detections were from December to April as well. A key predictor for blue whale distribution and movement in the California Current region has been identified with zooplankton aggregations, paying a particular attention to those euphausiid species, such as E. pacifica and T. spinifera, which are blue whale favorite krill. The Southern California Bight experiences seasonal upwelling, resulting in an increase of productivity and prey availability. The summer and early fall have been marked as the most favorable periods. This supports the presence of blue whales in the area at that time, supposing these marine mammals exploit the region as a feeding ground. (2) As to the interannual abundance during 2007-2012, I found a large variability. I observed a great increase of vocalizations in 2007 and 2010, whereas a decrease was shown in the other years, which is well marked in 2009. It is my belief that these fluctuations in abundance of D calls detections through the deployed period are due to the alternation of El Nino and La Nina events, which occurred in those years. (3) The assessment of the daily timing of D calls production shows that D calls are more abundant during the day than during the night with a peak at 12:00 and 13:00. Assuming that D calling is associated with feeding, the daily pattern of D calls may be linked to the prey availability. E. pacifica and T. spinifera are among those species of krill which undertake daily vertical migrations, remaining at depth during the day and slowly coming up towards the surface at night. Because of some anatomical arrangements, these euphausiids are very sensitive to the light. Given that we believe D calls have a social function, I hypothesize that blue whales may recognize the hours at the highest solar incidence as the best moment of the day in terms of prey availability, exploiting this time window to advert their conspecifics.

Common parietal activation in musical mental transformations across pitch and time

We previously observed that mental manipulation of the pitch level or temporal organization of melodies results in functional activation in the human intraparietal sulcus (IPS), a region also associated with visuospatial transformation and numerical calculation. Two outstanding questions about these musical transformations are whether pitch and time depend on separate or common processing in IPS, and whether IPS recruitment in melodic tasks varies depending upon the degree of transformation required (as it does in mental rotation). In the present study we sought to answer these questions by applying functional magnetic resonance imaging while musicians performed closely matched mental transposition (pitch transformation) and melody reversal (temporal transformation) tasks. A voxel-wise conjunction analysis showed that in individual subjects, both tasks activated overlapping regions in bilateral IPS, suggesting that a common neural substrate subserves both types of mental transformation. Varying the magnitude of mental pitch transposition resulted in variation of IPS BOLD signal in correlation with the musical key-distance of the transposition, but not with the pitch distance, indicating that the cognitive metric relevant for this type of operation is an abstract one, well described by music-theoretic concepts. These findings support a general role for the IPS in systematically transforming auditory stimulus representations in a nonspatial context. (C) 2013 Elsevier Inc. All rights reserved.

Geophysical Analysis of Seasonal Montandon Gravel Ridge Water Table Fluctuation and Moisture Gradient Variation due to Storm Events

The purpose of this research project is to continue exploring the Montandon Long-Term Hydrologic Research Site(LTHR) by using multiple geophysical methods to obtain more accurate and precise information regarding subsurface hydrologic properties of a local gravel ridge,which are important to both the health of surrounding ecosystems and local agriculture. Through using non-invasive geophysical methods such as seismic refraction, Direct Current resistivity and ground penetrating radar (GPR) instead of invasive methods such as boreholedrilling which displace sediment and may alter water flow, data collection is less likely to bias the data itself. In addition to imaging the gravel ridge subsurface, another important researchpurpose is to observe how both water table elevation and the moisture gradient (moisture content of the unsaturated zone) change over a seasonal time period and directly after storm events. The combination of three types of data collection allows the strengths of each method combine together and provide a relatively strongly supported conclusions compared to previous research. Precipitation and geophysical data suggest that an overall increase in precipitation during the summer months causes a sharp decrease in subsurface resistivity within the unsaturated zone. GPR velocity data indicate significant immediate increase in moisture content within the shallow vadose zone (< 1m), suggesting that rain water was infiltrating into the shallow subsurface. Furthermore, the combination of resistivity and GPR results suggest that the decreased resistivity within the shallow layers is due to increased ion content within groundwater. This is unexpected as rainwater is assumed to have a DC resistivity value of 3.33*105 ohm-m. These results may suggest that ions within the sediment must beincorporated into the infiltrating water.

Detecting and resolving position-dependent temperature effects in real-time quantitative polymerase chain reaction

Real-time quantitative polymerase chain reaction (qPCR) depends on precise temperature control of the sample during cycling. In the current study, we investigated how temperature variation in plate-based qPCR instruments influences qPCR results. Temperature variation was measured by amplicon melting analysis as a convenient means to assess well-to-well differences. Multiple technical replicates of several SYBR Green I-based qPCR assays allowed correlation of relative well temperature to quantification cycle. We found that inadequate template denaturation results in an inverse correlation and requires increasing the denaturation temperature, adding a DNA destabilizing agent, or pretreating with a restriction enzyme. In contrast, inadequate primer annealing results in a direct correlation and requires lowering the annealing temperature. Significant correlations were found in 18 of 25 assays. The critical nature of temperature-dependent effects was shown in a blinded study of 29 patients for the diagnosis of Prader-Willy and Angelman syndromes, where eight diagnoses were incorrect unless temperature-dependent effects were controlled. A method to detect temperature-dependent effects by pairwise comparisons of replicates in routine experiments is presented and applied. Systematic temperature errors in qPCR instruments can be recognized and their effects eliminated when high precision is required in quantitative genetic diagnostics and critical complementary DNA analyses.

Color variation in museum specimens of birds: effects of stress, pigmentation, and duration of storage

Animal coloration often serves as a signal to others that may communicate traits about the individual such as toxicity, status, or quality. Colorful ornaments in many animals are often honest signals of quality assessed by mates, and different colors may beproduced by different biochemical pigments. Investigations of the mechanisms responsible for variation in color expression among birds are best when including a geographically and temporally broad sample. In order to obtain such a sample, studies such as this often use museum specimens; however, in order for museum specimens toserve as an accurate replacement, they must accurately represent living birds, or we must understand the ways in which they differ. In this thesis, I investigated the link between feather corticosterone, a hormone secreted in response to stress, and carotenoid-basedcoloration in the Red-winged Blackbird (Agelaius phoeniceus) in order to explore a mechanistic link between physiological state and color expression. Male Red-winged Blackbirds with lower feather corticosterone had significantly brighter red epaulets than birds with higher feather corticosterone, while I found no significant changes in red chroma. I also performed a methodological comparison of color change in museum specimens among different pigment types (carotenoid and psittacofulvin) and pigments in different locations in the body (feather and bill carotenoids) in order to quantify colorchange over time. Carotenoids and psittacofulvins showed significant reductions in red brightness and chroma over time in the collection, and carotenoid color changed significantly faster than psittacofulvin color. Both bill and feather carotenoids showed significant reductions in red brightness and red chroma over time, but change of both red chroma and red brightness occurred at a similar rate in feathers and bills. In order to use museum specimens of ecological research on bird coloration specimen age must be accounted for before the data can be used; however, once this is accomplished, museum- based color data may be used to draw conclusions about wild populations.

DECOMPOSITION OF REGRESSION ESTIMATORS TO EXPLORE THE INFLUENCE OF "UNMEASURED" TIME-VARYING CONFOUNDERS

In environmental epidemiology, exposure X and health outcome Y vary in space and time. We present a method to diagnose the possible influence of unmeasured confounders U on the estimated effect of X on Y and to propose several approaches to robust estimation. The idea is to use space and time as proxy measures for the unmeasured factors U. We start with the time series case where X and Y are continuous variables at equally-spaced times and assume a linear model. We define matching estimator b(u)s that correspond to pairs of observations with specific lag u. Controlling for a smooth function of time, St, using a kernel estimator is roughly equivalent to estimating the association with a linear combination of the b(u)s with weights that involve two components: the assumptions about the smoothness of St and the normalized variogram of the X process. When an unmeasured confounder U exists, but the model otherwise correctly controls for measured confounders, the excess variation in b(u)s is evidence of confounding by U. We use the plot of b(u)s versus lag u, lagged-estimator-plot (LEP), to diagnose the influence of U on the effect of X on Y. We use appropriate linear combination of b(u)s or extrapolate to b(0) to obtain novel estimators that are more robust to the influence of smooth U. The methods are extended to time series log-linear models and to spatial analyses. The LEP plot gives us a direct view of the magnitude of the estimators for each lag u and provides evidence when models did not adequately describe the data.

Variation of the mechanical properties of PMMA to suit osteoporotic cancellous bone

Poly(methyl methacrylate) (PMMA) is by far the most frequently used bone substitute material for vertebroplasty. However, there are serious complications, such as cement leakage and an increased fracture rate of the adjacent vertebral bodies. The latter may be related to the mechanical properties of the augmented segment within the osteoporotic spine. A possible counter-measure is prophylactic augmentation at additional levels, but this aggravates the risk for the patient. Introduction of pores is a possible method to reduce the inherent high stiffness of PMMA. This study investigates the effect of porosity on the mechanical properties of PMMA bone cement. Different fractions of a highly viscous liquid were mixed into the PMMA during preparation. An open-porous material with adjustable mechanical properties resulted after removal of the aqueous phase. Different radiopacifiers were admixed to investigate their suitability for vertebroplasty. The final material was characterized mechanically by compressive testing, microscopically and radiologically. In addition, the monomer release subsequent to hardening was measured by means of gas chromatography. The Young's modulus in compression could be varied between 2800 +/- 70 MPa and 120 +/- 150 MPa, and the compression ultimate strength between 170 +/- 5 MPa and 8 +/- 9 MPa for aqueous fractions ranging between 0 and 50% of volume. Only a slight decrease of the Young's modulus and small changes of ultimate strength were found when the mixing time was increased. An organic hydrophilic and lipophilic radiopacifier led to a higher Young's modulus of the porous material; however, the ultimate strength was not significantly affected by adding different radiopacifiers to the porous cement. The radiopacity was lost after washing the aqueous phase out of the pores. No separation occurred between the aqueous and the PMMA phase during injection into an open porous ceramic material. The monomer released was found to increase for increasing aqueous fractions, but remained comparable in magnitude to standard PMMA. This study demonstrates that a conventional PMMA can be modified to obtain a range of mechanical properties, including those of osteoporotic bone.

Diel variation in a dynamic sexual display and its association with female mate-searching behaviour

Dynamic sexual signals often show a diel rhythm and may vary substantially with time of day. Diel and short-term fluctuations in such sexual signals pose a puzzle for condition capture models of mate choice, which assume a female preference for male traits that reliably reflect a male's quality. Here we experimentally manipulated the food supply of individual male field crickets Gryllus campestris in their natural habitat in two consecutive seasons to determine (i) the effect of male nutritional condition on the fine-scaled variation of diel investment in acoustic signalling and (ii) the temporal association between the diel variation in male signalling and female mate-searching behaviour. Overall food-supplemented males signalled more often, but the effect was only visible during the daytime. In the evening and the night, signal output was still high but the time spent signalling was unrelated to a male's nutritional condition. Females' mate-searching behaviour also showed a diel rhythm with peak activity during the afternoon, when differences among calling males were highest, and where signal output reliably reflects male quality. These findings suggest that males differing in nutritional condition may optimize their investment in signalling in relation to time of day as to maximize mating success.

Investigating within-canopy variation of functional traits and cellular structure of sugar maple (Acer saccharum) leaves

Patterns of increasing leaf mass per area (LMA), area-based leaf nitrogen (Narea), and carbon isotope composition (δ13C) with increasing height in the canopy have been attributed to light gradients or hydraulic limitation in tall trees. Theoretical optimal distributions of LMA and Narea that scale with light maximize canopy photosynthesis; however, sub-optimal distributions are often observed due to hydraulic constraints on leaf development. Using observational, experimental, and modeling approaches, we investigated the response of leaf functional traits (LMA, density, thickness, and leaf nitrogen), leaf carbon isotope composition (δ13C), and cellular structure to light availability, height, and leaf water potential (Ψl) in an Acer saccharum forest to tease apart the influence of light and hydraulic limitations. LMA, leaf and palisade layer thickness, and leaf density were greater at greater light availability but similar heights, highlighting the strong control of light on leaf morphology and cellular structure. Experimental shading decreased both LMA and area-based leaf nitrogen (Narea) and revealed that LMA and Narea were more strongly correlated with height earlier in the growing season and with light later in the growing season. The supply of CO2 to leaves at higher heights appeared to be constrained by stomatal sensitivity to vapor pressure deficit (VPD) or midday leaf water potential, as indicated by increasing δ13C and VPD and decreasing midday Ψl with height. Model simulations showed that daily canopy photosynthesis was biased during the early growing season when seasonality was not accounted for, and was biased throughout the growing season when vertical gradients in LMA and Narea were not accounted for. Overall, our results suggest that leaves acclimate to light soon after leaf expansion, through an accumulation of leaf carbon, thickening of palisade layers and increased LMA, and reduction in stomatal sensitivity to Ψl or VPD. This period of light acclimation in leaves appears to optimize leaf function over time, despite height-related constraints early in the growing season. Our results imply that vertical gradients in leaf functional traits and leaf acclimation to light should be incorporated in canopy function models in order to refine estimates of canopy photosynthesis.