The clonal population structure of <em>Daphnia</em> spp. in Lake Maarsseveen, a small mesotrophic lake with a maximum depth of 32 m, was studied from April 1989 to July 1991. During this period three distinct periods of diel vertical migration (DVM) occurred. <em>Daphnia galeata</em> and the hybrid <em>D. galeata x D. hyalina</em> were found, the former for a restricted period from June 1989 to December 1990. Both 'species' showed genetic variation at the <em>Pgm</em> locus and high temporal fluctuations in genotype frequencies. These fluctuations and DVM were not related. During 1991 a single hybrid genotype reached frequencies of more than 95%. The relation between clonal composition and DVM of <em>Daphnia</em> in Lake Maarsseveen is discussed.

The problem of organizing collective action campaigns is tackled with a multiagent simulation, in which the actor’s decision to participate is modeled on the basis of an expansion of the social psychological Theory of Planned Behavior. The variables entering into the model of the individual’s decision to participate in a collective action are attitude, return, subjective social norm, and perceived behavioral control. With these four variables, various social scientific theories become integrated (Elaboration Likelihood Model, Theory of Planned Behavior, Rational Choice Theory). The theories allow conceptualization of interactions among individuals, and the effect of activators, who seek to recruit others to participate in a collective action, can be studied. The Simulations of a population of 10,000 different agents presented in this paper reveal the influence of the following factors on the effectiveness of collective action campaigns: The dynamics of creating the collective good, forms of recruitment by activators (allor- none contracts), the size of the collective good, and the resources available to activators (training in persuasion methods, possibility to reward participants).

Sediment cores around Antarctica provide a unique opportunity to cross check and supplement the climatic information recorded in ice cores. Suitable high-resolution data, however, have not been available until now from East Antarctica. We present results from the longest continuous postglacial marine sediment succession (1290 cm) ever obtained from an East Antarctic basin. Twenty-one radiocarbon dates show a consistent age to depth correlation over the last 9400 calibrated years BP (cal. yr BP). For this time interval distinct changes in the silicified ice-related biotic species assemblages, accumulation rates of organic carbon, δ¹³C values, and C/N ratios were detected. We demonstrate that these sediment signatures can be used as climate proxies. Our results indicate significant Holocene climatic variability with a climatic optimum between 3500 and 2500 cal. yr BP. This was followed by an abrupt and dramatic cooling that took place within less than 200 yr. Corroborating the results of other researchers we hypothesize that this climatic optimum and its termination was a circumantarctic event which would appear to be out of phase with a proposed global temperature trend (maximum) during the Holocene.

Resting eggs of planktonic organisms from datable sediment cores are increasingly used to reconstruct historical information on the abundance, size, genetic composition, and microevolution of planktonic organisms. All of these studies have relied on the (up to now) mostly untested assumption that the resting egg bank in sediment will indeed allow an accurate reconstruction of past populations. Here we test the performance of the egg bank to reconstruct historical data of the <I>Daphnia</I> population of Lake Constance, which was thoroughly investigated throughout the past century. We show that it is possible to reproduce the variability in the abundance, size, and genetic composition of <I>Daphnia galeata</I> within a period of ∼2 decades. Furthermore, resting egg data allowed us to reconstruct the timing of the invasion of <I>D. galeata</I> into Lake Constance. However, the egg bank did not reconstruct (1) the dynamics of the native <I>Daphnia</I> species of Lake Constance, <I>D. hyalina</I>, and (2) the relative importance of the two <I>Daphnia</I> species. We present evidence that the latter is caused by differences in the sexually reproductive activity between the two species. The failure to reconstruct the long-term dynamics of <I>D. hyalina</I> in the lake is most probably due to a change in the frequency and timing of sexual activity during the course of eutrophication.

Detecting small amounts of genetic subdivision across geographic space remains a persistent challenge. Often a failure to detect genetic structure is mistaken for evidence of panmixia, when more powerful statistical tests may uncover evidence for subtle geographic differentiation. Such slight subdivision can be demographically and evolutionarily important as well as being critical for management decisions. We introduce here a method, called spatial analysis of shared alleles (SAShA), that detects geographically restricted alleles by comparing the spatial arrangement of allelic co-occurrences with the expectation under panmixia. The approach is allele-based and spatially explicit, eliminating the loss of statistical power that can occur with user-defined populations and statistical averaging within populations. Using simulated data sets generated under a stepping-stone model of gene flow, we show that this method outperforms spatial autocorrelation (SA) and Φ_ST under common real-world conditions: at relatively high migration rates when diversity is moderate or high, especially when sampling is poor. We then use this method to show clear differences in the genetic patterns of 2 nearshore Pacific mollusks, <em>Tegula funebralis</em> (= <em>Chlorostoma funebralis</em>) and <em>Katharina tunicata</em>, whose overall patterns of within-species differentiation are similar according to traditional population genetics analyses. SAShA meaningfully complements Φ_ST/<em>F</em>_ST, SA, and other existing geographic genetic analyses and is especially appropriate for evaluating species with high gene flow and subtle genetic differentiation.

Im vorliegenden Feldexperiment zum sparsamen Umgang mit Elektrizität wurde in einer mittelgroßen Gemeinde untersucht, ob die Wirksamkeit von Information mit verschiedenen Kombinationen bewährter umweltpsychologischer Interventionsinstrumente gesteigert werden kann. Gleichzeitig wurde eine neue Methode getestet, Interventionsinstrumente weiterzuverbreiten und bei den angestrebten Zielgruppen zur Wirkung zu bringen. Die Stromsparaktion gliederte sich in zwei Phasen: eine Diffusionsphase und eine Interventionsphase mit vier experimentellen Bedingungen. In der Diffusionsphase wurden Diffusionsinstrumente in Form von Abreißblöcken mit Rücksendekarten an fünfzig zufällig ausgewählte Personen verteilt, die sie gemäß einer Instruktion an Bekannte und Nachbarn weitergeben sollten. Mit Hilfe der Rücksendekarten wurden eine Baseline-Messung des Stromzählerstands sowie Adressen potentieller Teilnehmer gewonnen. In der nachfolgenden, einen Monat dauernden Interventionsphase wurden die Teilnahmewilligen zufällig vier Interventionsgruppen zugeteilt: nur Information; Information und Selbstfeedback; Information und private, schriftliche Selbstverpflichtung sowie eine Kombination von Information, Selbstverpflichtung und Selbstfeedback. Außerdem wurde eine Kontrollgruppe gebildet, bei der lediglich der Stromverbrauch gemessen wurde. Einerseits zeigte sich, dass die instruierte Selbstverbreitung als neuartiges Diffusionsinstrument gut funktionierte, anderseits konnten sowohl die Verbrauchsreduktionen in der Größenordnung von 10%, die sich auch anlässlich einer unangekündigten Nachmessung vier Wochen nach Abschluss des Experiments als stabil erwiesen hatten, als auch die Unterschiede zwischen den Interventionsbedingungen statistisch leider nicht gesichert werden.

<b>Aim</b> Current estimates of species richness within rapidly evolving species flocks are often highly dependent on the species status of allopatric populations that differ in phenotypic traits. These traits may be unreliable indicators of biological species status and systematists may have inconsistently assigned species among lineages or locations on the basis of these traits, thus hampering comparative studies of regional species richness and speciation rates. Our aim was to develop a method of generating standardized estimates of regional species richness suitable for comparative analysis, and to use these estimates to examine the extent and consistency of species assignment of allopatric populations within rapidly evolving cichlid fish flocks present in three east African lakes.<br/> <b>Location</b> Lakes Malawi, Victoria and Tanganyika.<br/> <B>Methods</B> Using published taxon co-occurrence data, a novel approach was employed to calculate standardized 'minimum' estimates of regional species richness for hard substrate associated complexes of cichlids within each of the lakes. Minimum estimates were based on an explicit assumption that if taxa present on equivalent habitats have disjunct distributions, then they are allopatric forms of the same species. These estimates were compared with current observed 'high-end' regional species richness estimates for those complexes to determine the consistency of species assignment of allopatric populations between lineages within a lake. A 'sympatry' index was developed to enable comparisons of levels of species assignment of allopatric populations between-lakes to be made.<br/> <B>Results</B> Within each lake, the minimum and high-end estimates for species richness were significantly correlated across complexes, indicating that the complexes that contain more recognized species contain the most genuine biological species. However, comparisons of complexes among lakes revealed considerable differences. For equivalent geographical areas, substantially higher proportions of recognized species were totally allopatric within the studied Lake Malawi and Lake Victoria complexes, than those of Lake Tanganyika.<br/> <B>Main</B> Conclusions Among African lakes, levels of assignment to species status of allopatric populations were found to be distinctly different. It is unclear whether the discrepancies are a consequence of differences between the lake faunas in degrees of phenotypic divergence among allopatric populations, or are simply the result of inconsistent taxonomic practices. In either case, these results have considerable wider relevance for they emphasize that quantitative measures of regional and beta diversity are critically dependent on the species status of allopatric populations, an issue usually neglected in comparative studies of species richness. The technique introduced here can be used to standardize measures of regional diversity of lineages for comparative analyses, potentially enabling more accurate identification of processes influencing rates of speciation.

Evaluating uncertainty in solute transport under nonstationary flow conditions is a computationally demanding task. This is particularly true for cases with a two-point covariance function of log conductivity depending on the actual positions of the points rather than their distance vector. These may occur when the geological formation exhibits a trend. Nonstationarity can also be the result of uncertainty in the trend parameters of the mean log conductivity value, or it may originate from conditioning of the log conductivity field to measurements of, for example, head or conductivity. We present an efficient numerical method for evaluating the variance of travel time in such formations. We cover cases in which the nonstationary covariance functions are constructed from stationary counterparts, either by scaling functions or by summation with nonstationary functions resulting from marginalization or conditioning. We apply a matrix-based first- order second-moment (FOSM) method for uncertainty propagation, using the continuous adjoint-state method for coupled systems to evaluate the sensitivity matrix. The resulting matrix-matrix multiplications are accelerated by fast Fourier transformation (FFT) techniques after periodic embedding of the covariance matrices referring to the stationary counterparts. The combination of these methods makes it possible to compute the travel time uncertainty in domains discretized by several hundred thousand log conductivity values on standard personal computers within a reasonable time-frame. For demonstration, we apply the method to a binary medium and a medium exhibiting a continuous trend in the covariance function. In the latter application we also demonstrate the effects of marginalization and conditioning.

The Quasi-Linear Geostatistical Approach is a method of inverse modeling to identify parameter fields, such as the hydraulic conductivity in heterogeneous aquifers, given observations of related quantities like hydraulic heads or arrival times of tracers. Derived in the Bayesian framework, it allows to rigorously quantify the uncertainty of the identified parameter field. Since inverse modeling in subsurface flow is in general a non-linear problem, the Quasi-Linear Geostatistical Approach employs an algorithm for non-linear optimization. Up to presence, this algorithm has been similar to the Gauss-Newton algorithm for least-squares fitting and fails in cases of strong non-linearity. In this study, we present and discuss a new modified Levenberg-Marquardt algorithm for the Quasi-Linear Geostatistical Approach. Compared to the original method, the new algorithm offers increased stability and is more robust, allowing for stronger on-linearity and higher variability of the parameter field to be identified. We demonstrate its efficiency and improved convergence compared to the original version in several test cases. The new algorithm is designed for the general case of an uncertain mean of the parameter field, which includes the cases of completely known and entirely unknown mean as special cases.

Numerical and theoretical studies have indicated that pore- scale mixing can be the limiting process for reactions among dissolved compounds in porous media. It has been claimed that multicomponent reactions in porous media could be accurately estimated using mixing coefficients obtained from point-like measurements of conservative tracer concentrations. In this study, we verify these concepts experimentally by tracer tests in a homogeneously packed saturated sand column. Fiber-optic fluorometry was applied to detect point-related concentrations of fluorescein, which was used as both the conservative and the reactive tracer. In the reactive tracer experiment, an acidic solution containing the tracer was displaced by an alkaline solution without tracer. Since the fluorescence of fluorescein is quenched at low pH, the fluorescence intensity measured in the reactive breakthrough curve indicated the mixing of the two solutions. The measured reactive breakthrough curves were compared to predictions based on the conservative breakthrough curves. Predictions and measurements agreed well. Our results imply that incomplete mixing on the pore scale is of minor significance for field-scale applications. On this scale, however, even weak sorption might influence mixing significantly.

The performance of four microscale toxicity bioassays conducted on whole sediments was evaluated during a bioremediation project undertaken in 1999-2000 on a crude oil-contaminated freshwater shoreline of the St. Lawrence River, Quebec, Canada. The toxicity tests assessed included: (1) the Microtox^® solid-phase assay (MSPT), (2) the Biotox^TM Flash solid-phase test (Flash), (3) the algal solid-phase assay (ASPA), and 4) the Ostracodtoxkit solid-phase assay. Data generated with these assays were compared with those obtained using the standard endobenthic amphipod (<I>Hyalella azteca</I>) bioassay. Bioanalytical comparisons indicated that all five solid-phase tests were useful in detecting the toxicity of oiled sediments; however, statistical analyses distinguished a difference in response between the invertebrate (amphipod and Ostracodtoxkit) and bacterial luminescence tests (MSPT and Flash). Based on these results, it is recommended that careful selection of biotests be made in the design of the test battery for assessment of residual oil sediment toxicity. Time-series toxicity data generated with ASPA indicated that oiled sediments in the freshwater wetlands of the St. Lawrence River remained toxic to phytoplankton for at least 65 weeks and that remediation treatment was able to accelerate detoxification by 16 weeks.

A pronounced decline in catch of brown trout (<I>Salmo trutta</I> L.) over the last 10–20 years has been reported for many rivers in Switzerland. Impaired health status of the fishes has been suggested as one possible cause of the decline. The present study investigated the health status of juvenile brown trout from four Swiss rivers which experienced reductions of brown trout catches during the last two decades: Emme, Liechtensteiner Binnenkanal (LBK), Necker and Venoge. A gradient approach was applied, studying at each river a headwater (HW), midstream (D1) and downstream site (D2). Fish health was assessed by the following indices: hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity, organ (liver, kidney) histopathology, and gross biometric indices (condition factor, hepatosomatic index). Hepatic EROD activities were generally low without showing significant within- or between-stream differences. Histopathological alterations of the liver displayed a moderate downstream increase in the Emme, LBK and Necker, but not in the Venoge. Between-stream differences of liver pathology were small. Kidney histopathology was not different between upstream and downstream sites, except for Emme and Venoge, where fishes at the downstream sites were infected with the parasite <I>Tetracapsuloides bryosalmonae</I>, the cause of the proliferative kidney disease (PKD). The findings from this study point to an association of within-stream gradients in water quality, PKD prevalence, fish health and brown trout biomass, whereas between-stream differences of actual fish health status reflecting the different levels of catch declines observed in the four rivers during the last two decades are not evident.

Mineralogical composition and pore fluid pressure are the crucial controls for mechanical stability of water-saturated sediments. Their in situ measurements were undertaken in earthquake-triggered slope deposits in Lake Lucerne (Switzerland) in addition to geophysical characterization and laboratory index properties, shear and consolidation experiments on core. Two lithological units were identified: A weak, lightly underconsolidated section of postglacial silty clays overlies overconsolidated fine-grained glacial deposits with coarser components and excess fluid pressure (ca. 2.5 × higher than in the hanging wall clay). In the event of an earthquake, hydrofracturing in the overconsolidated section facilitates an upward pore pressure pulse to the base of the softer, less stable unit. Here, excess pore pressure initiates sliding along a failure plane at the lithological boundary, causing the entire postglacial sedimentary section to slip downslope. We propose that many submarine landslides at active and passive continental margins may follow this mechanism of pore pressure-induced failure.

The Minqin Basin is a type area for examining stress on groundwater resources in the Gobi Desert, and has been investigated here using a combination of isotopic, noble gas and chemical indicators. The basin is composed of clastic sediments of widely differing grain size and during the past half century over 10 000 boreholes have been drilled with a groundwater decline of around 1 m a<SUP>-1</SUP>. Modern diffuse recharge is unlikely to exceed 3 mm a<SUP>-1</SUP>, as determined using unsaturated zone profiles and Cl<SUP>-</SUP> mass balance. A small component of modern (<50 a) groundwater is identified in parts of the basin from <SUP>3</SUP>H-<SUP>3</SUP>He data, probably from irrigation returns. A clear distinction is found between modern waters with median δ<SUP>18</SUP>O values of 6.5 ± 0.5‰ and most groundwaters in the basin with more depleted isotopic signatures. Radiocarbon values as pmc range from 0.6% to 85% modern, but it is difficult to assign absolute ages to these, although a value of 20% modern C probably represents the late Pleistocene to Holocene transition. The δ<SUP>13</SUP>C compositions remain near-constant throughout the basin (median value of -8.1‰ δ<SUP>13</SUP>C) and indicate that carbonate reactions are unimportant and also that little reaction takes place. There is a smooth decrease in <SUP>14</SUP>C activity accompanied by a parallel increase in <SUP>4</SUP>He accumulations from S-N across the basin, which define the occurrence of a regional flow system. Noble gas temperatures indicate recharge temperatures of about 5.6 °C for late Pleistocene samples, which is some 2-3 °C cooler than the modern mean annual air temperature and the recharge temperature obtained from several Holocene samples. Groundwaters in the Minqin Basin have salinities generally below 1 g/L and are aerobic, containing low Fe but elevated concentrations of U, Cr and Se (mean values of 27.5, 5.8 and 5.3 μg L<SUP>-1</SUP>, respectively). Nitrate is present at baseline concentrations of around 2 mg L<SUP>-1</SUP> but there is little evidence of impact of high NO<SUB>3</SUB> from irrigation returns. Strontium isotope and major ion ratios suggest that silicate reactions predominate in the aquifer. The results have important implications for groundwater management in the Minqin and other water-stressed basins in NW China - a region so far destined for rapid development. The large proportion of the water being used at present is in effect being mined and significant changes are urgently needed in water use strategy.

An increasing number of studies have documented phenotypic selection on life-history traits in human populations, but less is known of the heritability and genetic constraints that mediate the response to selection on life-history traits in humans. We collected pedigree data for four generations of preindustrial (1745-1900) Finns who lived in premodern fertility and mortality conditions, and by using a restricted maximum-likelihood animal-model framework, we estimated the heritability of and genetic correlations between a suite of life-history traits and two alternative measures of fitness. First, we demonstrate high heritability of key life-history traits (fecundity, interbirth interval, age at last reproduction, and adult longevity) and measures of fitness (individual lambda and lifetime reproductive success) for females but not for males. This sex difference may have arisen because most of the measured traits are under physiological control of the female, such that a male's fitness in monogamous societies may depend mainly on the reproductive quality of his spouse. We found strong positive genetic correlations between female age at first reproduction and longevity, and between interbirth intervals and longevity, suggesting reduced life spans in females who either started to breed relatively early or who then bred frequently. Our results suggest that key female life-history traits in this premodern human population had high heritability and may have responded to natural selection. However genetic constraints between longevity and reproductive life-history traits may have constrained the evolution of life history and facilitated the maintenance of additive genetic variance in key life-history traits.

Adaptive radiations are an important source of biodiversity, but resolving which ecological pressures seed these processes in natural systems remains difficult. Here the adaptive radiation among <I>Telmatherina</I>, a genus of freshwater fish endemic to an ancient lake in central Sulawesi, Indonesia, was examined to determine its causal root. We demonstrate that all <I>Telmatherina</I> in this lake can be categorized into three lineages each possessing specialized skull shapes and pharyngeal jaw bones allowing them to exploit different resources. These data demonstrate a natural example of how resource partitioning has likely initiated adaptive radiation in a resource limited environment.

Expression profiling of exposed cells or organisms can reveal genes sensitive to environmental contaminants or toxic compounds. However, the mechanistic relevance of altered gene expression often remains to be elucidated. Toxicant-dependent differential gene expression may indicate protection to or mediation of toxicity. Previous studies revealed a number of differentially transcribed genes in zebrafish embryos exposed to the model compound 3,4-dichloroaniline (3,4-DCA). To evaluate the significance of two of the most sensitive genes, cytochrome P 450 1a (<I>cyp1α</I>) and heme oxygenase 1 (<I>hmox1</I>), for 3,4-DCA toxicity, RNA interference-mediated knockdown and overexpression studies have been conducted. Knockdown of gene transcription by siRNA for <I>cyp1α</I> and <I>hmox1</I> enhanced the frequency of developmental disorders in embryos exposed to 3,4-DCA. Vice versa, injection of <I>cyp1α</I> and <I>hmox1</I> mRNA reduced the number of disorders. The opposite effects of siRNA and mRNA injection clearly indicate a protective role of the corresponding proteins. Functional studies such as the one presented could be applied to a wide variety of genes. They would be ideally suited to study the role of genes identified from toxicogenomic studies in the zebrafish embryo model.

High-iron sediments in North Haiwee Reservoir (Olancha, CA), resulting from water treatment for removal of elevated dissolved arsenic in the Los Angeles Aqueduct system, were studied to examine arsenic partitioning between solid phases and porewaters undergoing shallow burial. To reduce arsenic in drinking water supplies, ferric chloride and a cationic polymer coagulant are added to the aqueduct upstream of Haiwee Reservoir, forming an iron-rich floc that scavenges arsenic from the water. Analysis by synchrotron X-ray absorption spectroscopy (XAS) showed that the aqueduct precipitate is an amorphous hydrous ferric oxide (HFO) similar to ferrihydrite, and that arsenic is associated with the floc as adsorbed and/or coprecipitated As(V). Arsenic-rich floc and sediments are deposited along the inlet channel as aqueduct waters enter the reservoir. Sediment core samples were collected in two consecutive years from the edge of the reservoir along the inlet channel using 30- or 90-cm push cores. Cores were analyzed for total and extractable arsenic and iron concentrations. Arsenic and iron speciation and mineralogy in sediments were examined at selected depths by synchrotron XAS and X-ray diffraction (XRD).Sediment–porewater measurements were made adjacent to the core sample sites using polyacrylamide gel probe samplers. Results showed that sediment As(V) is reduced to As(III) in all cores at or near the sediment–water interface (0–4 cm), and only As(III) was observed in deeper sediments. Analyses of EXAFS spectra indicated that arsenic is present in the sediments mostly as a bidentate–binuclear, inner-sphere sorption complex with local atomic geometries similar to those found in laboratory studies. Below about 10 cm depth, XAS indicated that the HFO floc had been reduced to a mixed Fe(II, III) solid with a local structure similar to that of synthetic green rust (GR) but with a slightly contracted average interatomic Fe–Fe distance in the hydroxide layer. There was no evidence from XRD for the formation of a crystalline GR phase. The release of dissolved iron (presumably Fe<SUP>2+</SUP>) and arsenic to solution, as monitored by <I>in situ</I> gel probes, was variable but, in general, occurred at greater depths than arsenic reduction in the sediments by spectroscopic observations and appears to be near or below the depth at which sediment GR was identified. These data point to reductive dissolution of the sorbent iron phase as the primary mechanism of release of sorbed arsenic to solution.

Located at 54º S in the heart of the Island of Tierra del Fuego, Lago Fagnano occupies the deepest of a chain of <I>en-echelon</I> tectonic depressions along the Magallanes-Fagnano Transform system (MFT). A recent geophysical campaign combining 3.5 kHz (pinger) single-channel with 1 in3 airgun multi-channel systems surveyed more than 100 m of glacio-lacustrine sediments filling two main sub-basins. These data provide a unique opportunity to visualize the most recent lacustrine sequence with high-resolution while simultaneously imaging the oldest infill. A preliminary seismic stratigraphic analysis of the high-resolution 3.5 kHz pinger data allowed the identification of three major seismostratigraphic units (A, the oldest and C, the youngest). While unit A is interpreted as glacially derived sediments, the overlying unit B is interpreted as fining upward sequences of proglacial turbidites reflecting sediment pulses released by the retreating Fagnano glacier during the last deglaciation. A major environmental change occurred during deposition of unit C when pelagic style of sedimentation is intercalated by sequences of downslope mass flow events probably triggered by relatively strong tectonic pulses along the MFT system. Gravity cores show a regular alternation of light and dark laminae occasionally interrupted by homogenous sedimentary units interpreted as turbidites. Ultra-high resolution X-ray fluorescence micro-profiles show fluctuations in major trace elements at mm scale that may indicate seasonal variations in the sedimentary influx. These core data provide a unique record of decadal changes in regional climate that can be compared with other marine and continental archives to improve our understanding of the forcing mechanisms behind climate change.

Background: Orthologous genes are frequently presumed to perform similar functions. However, outside of model organisms, this is rarely tested. One means of inferring changes in function is if there are changes in the level of gene conservation and selective constraint. Here we compare levels of gene conservation across three bacterial groups to test for changes in gene functionality.<br /> Findings: The level of gene conservation for different orthologous genes is highly correlated across clades, even for highly divergent groups of bacteria. These correlations do not arise from broad differences in gene functionality (e.g. informational genes vs. metabolic genes), but instead seem to result from very specific differences in gene function. Furthermore, these functional differences appear to be maintained over very long periods of time.<br /> Conclusion: These results suggest that even over broad time scales, most bacterial genes are under a nearly constant level of purifying selection, and that bacterial evolution is thus dominated by selective and functional stasis.

In this study the effects of 3,4-dichloroaniline (3,4-DCA), a decomposition product of the herbicides propanil and diuron (and other pesticides), and diazinon, a neurotoxic insecticide, on early life stages of zebrafish <I>Danio rerio</I> were assessed. The toxicity of these substances with different modes of action (acetylcholine esterase inhibitor vs. polar narcosis) was tested for single substances as well as in binary mixtures. To study effects on different biological organisation levels (from the molecular up to the whole organism level) the molecular stress response regarding Hsp70, the embryonic and larval development and the locomotor activity were investigated as integrative biomarkers. In single substance tests 3,4-dichloroaniline elicited deformations at ≥0.25 mg/l during the 11 days subchronic test, whereas locomotor activity and mortality were impaired at ≥0.5 mg/l. Diazinon effects on those parameters were obvious at ≥2 mg/l, except for the deformation rate (11 days:1 mg/l). In equitoxic mixtures of both substances concentration additivity was observed for deformation rate and mortality (11 days). An increase in the Hsp70 content occurred in zebrafish exposed to 0.25 mg 3,4-DCA/l as well as to 0.05 mg diazinon/l; in mixtures concentration additivity could be shown. The investigated endpoints varied in respect to their sensitivity, with deformations and Hsp70 levels as most sensitive parameters concerning 3,4-DCA and Hsp70 as most sensitive parameter concerning diazinon. Accordingly, for an integrated understanding of the effects of chemicals and their mixtures on fish, a battery of different test methods should be applied.