Isolation and characterization of ten polymorphic microsatellite markers for three cryptic Gammarus fossarum (Amphipoda) species

The ecologically important stream invertebrate Gammarus fossarum is a morphospecies that includes at least three genetically differentiated biological species. We developed ten microsatellite markers and tested them in a total of 208 individuals from all three known cryptic species (types A, B and C). All markers were polymorphic and successfully amplified in type A, nine in type B and five in type C. There were up to 11 alleles per marker and specie

Intrinsic incompatibilities evolving as a by-product of divergent ecological selection : Considering them in empirical studies on divergence with gene flow

The possibility of intrinsic barriers to gene flow is often neglected in empirical research on local adaptation and speciation with gene flow, for example when interpreting patterns observed in genome scans. However, we draw attention to the fact that, even with gene flow, divergent ecological selection may generate intrinsic barriers involving both ecologically selected and other interacting loci. Mechanistically, the link between the two types of barriers may be generated by genes that have multiple functions (i.e., pleiotropy), and/or by gene interaction networks. Because most genes function in complex networks, and their evolution is not independent of other genes, changes evolving in response to ecological selection can generate intrinsic barriers as a by-product. A crucial question is to what extent such by-product barriers contribute to divergence and speciation-that is whether they stably reduce gene flow. We discuss under which conditions by-product barriers may increase isolation. However, we also highlight that, depending on the conditions (e.g., the amount of gene flow and the strength of selection acting on the intrinsic vs. the ecological barrier component), the intrinsic incompatibility may actually destabilize barriers to gene flow. In practice, intrinsic barriers generated as a by-product of divergent ecological selection may generate peaks in genome scans that cannot easily be interpreted. We argue that empirical studies on divergence with gene flow should consider the possibility of both ecological and intrinsic barriers. Future progress will likely come from work combining population genomic studies, experiments quantifying fitness and molecular studies on protein function and interactions.Peer reviewe

Targeted re-sequencing reveals geographic patterns of differentiation for loci implicated in parallel evolution

Parallel divergence and speciation provide evidence for the role of divergent selection in generating biological diversity. Recent studies indicate that parallel phenotypic divergence may not have the same genetic basis in different geographical locations - "outlier loci" (loci potentially affected by divergent selection) are often not shared among parallel instances of phenotypic divergence. However, limited sharing may be due, in part, to technical issues if false positive outliers occur. Here, we test this idea in the marine snail Littorina saxatilis, which has evolved two partly isolated ecotypes (adapted to crab predation vs. wave action) in multiple locations independently. We argue that if the low extent of sharing observed in earlier studies in this system is due to sampling effects, we expect outliers not to show elevated FST when sequenced in new samples from the original locations, and also not to follow predictable geographical patterns of elevated FST . Following a hierarchical sampling design (within vs. between country), we applied capture sequencing, targeting outliers from earlier studies and control loci. We found that outliers again showed elevated levels of FST in their original location, suggesting they were not generated by sampling effects. Outliers were also likely to show increased FST in geographically close locations, which may be explained by higher levels of gene flow or shared ancestral genetic variation compared to more distant locations. However, in contrast to earlier findings, we also found some outlier types to show elevated FST in geographically distant locations. We discuss possible explanations for this unexpected result. This article is protected by copyright. All rights reserved

Cyclic Fatigue Crack Growth In PZT Piezoelectric Ceramics Induced By Mechanical Load

In this work the crack propagation behaviour of a commercially obtained lead zirconate titanate (PZT) piezoceramic is studied under monotonic and cyclic loading. Piezoelectric ceramics contain an electrical dipole in their crystal structure such that when a mechanical load is applied an electrical potential is formed, and vice versa. Permanent electrical domain orientation may be induced by the application of a large electrical potential in a process known as poling. Piezoelectric ceramics are used for applications such as actuators, sonar transducers and microphones. These and most other application involve high levels of cyclic loading and fatigue degradation is will known. However, cyclic fatigue to date has only been considered under electrical loading despite the fact that most components are subjected to high levels of mechanical load. Crack growth studies are rare. In the vicinity of a crack tip, local stress causes switching of the crystal domains leading to dilation perpendicular to the crack propagation direction. This explains the observed crack growth resistance (R-curve) toughening which is characterised in this work. Furthermore, it is shown that the extent of toughening is dependent upon the crack propagation direction relative to the poling direction. When a cyclic mechanical load is applied, subcritical crack growth is shown to occur below the plateau value of the R-curve and at rates which are independent of poling direction. A measurement of static fatigue rates show that a true cyclic fatigue degradation process exists. Another experiment which measured the R-curve behaviour as a function of intermittent loading time showed that the observed fatigue behaviour could not be explained by reverse switching of the crystal domains. The question arises therefore as to the mechanism of cyclic fatigue degradation in PZT and whether it is the same under both cyclic electrical and mechanical loading. In both cases it is currently unknown however a parallel study has shown that plastic strain accumulates in bulk PZT under mechanical loading in a strain-softening type process. The link between this and crack propagation behaviour will be discussed

Hidden Biodiversity in an Ecologically Important Freshwater Amphipod: Differences in Genetic Structure between Two Cryptic Species

Cryptic species, i.e. species that are morphologically hard to distinguish, have been detected repeatedly in various taxa and ecosystems. In order to evaluate the importance of this finding, we have to know in how far cryptic species differ in various aspects of their biology. The amphipod Gammarus fossarum is a key invertebrate in freshwater streams and contains several cryptic species. We examined the population genetic structure, genetic diversity and demographic history of two of them (type A and type B) using microsatellite markers and asked whether they show significant differences. We present results of population genetic analyses based on a total of 37 populations from the headwaters of two major European drainages, Rhine and Rhone. We found that, in both species, genetic diversity was geographically structured among and within drainages. For type A in the Rhine and type B in the Rhone, we detected significant patterns of isolation by distance. The increase of genetic differentiation with geographical distance, however, was much higher in type A than in type B. This result indicates substantial interspecific differences in population history and/or the extent of current gene flow between populations. In the Rhine, type B does not show evidence of isolation by distance, and population differentiation is relatively low across hundreds of kilometres. The majority of these populations also show signatures of recent bottlenecks. These patterns are consistent with a recent expansion of type B into the Rhine drainage. In summary, our results suggest considerable and previously unrecognized interspecific differences in the genetic structure of these cryptic keystone species

Is embryo abortion a post‐zygotic barrier to gene flow between Littorina ecotypes?

Genetic incompatibilities contribute to reproductive isolation between many diverging populations, but it is still unclear to what extent they play a role if divergence happens with gene flow. In contact zones between the "Crab" and "Wave" ecotypes of the snail Littorina saxatilis, divergent selection forms strong barriers to gene flow, while the role of post‐zygotic barriers due to selection against hybrids remains unclear. High embryo abortion rates in this species could indicate the presence of such barriers. Post‐zygotic barriers might include genetic incompatibilities (e.g. Dobzhansky–Muller incompatibilities) but also maladaptation, both expected to be most pronounced in contact zones. In addition, embryo abortion might reflect physiological stress on females and embryos independent of any genetic stress. We examined all embryos of >500 females sampled outside and inside contact zones of three populations in Sweden. Females' clutch size ranged from 0 to 1,011 embryos (mean 130 ± 123), and abortion rates varied between 0% and 100% (mean 12%). We described female genotypes by using a hybrid index based on hundreds of SNPs differentiated between ecotypes with which we characterized female genotypes. We also calculated female SNP heterozygosity and inversion karyotype. Clutch size did not vary with female hybrid index, and abortion rates were only weakly related to hybrid index in two sites but not at all in a third site. No additional variation in abortion rate was explained by female SNP heterozygosity, but increased female inversion heterozygosity added slightly to increased abortion. Our results show only weak and probably biologically insignificant post‐zygotic barriers contributing to ecotype divergence, and the high and variable abortion rates were marginally, if at all, explained by hybrid index of females

Using replicate hybrid zones to understand the genomic basis of adaptive divergence

Combining hybrid zone analysis with genomic data is a promising approach to understanding the genomic basis of adaptive divergence. It allows for the identification of genomic regions underlying barriers to gene flow. It also provides insights into spatial patterns of allele frequency change, informing about the interplay between environmental factors, dispersal and selection. However, when only a single hybrid zone is analysed, it is difficult to separate patterns generated by selection from those resulting from chance. Therefore, it is beneficial to look for repeatable patterns across replicate hybrid zones in the same system. We applied this approach to the marine snail Littorina saxatilis, which contains two ecotypes, adapted to wave-exposed rocks vs. high-predation boulder fields. The existence of numerous hybrid zones between ecotypes offered the opportunity to test for the repeatability of genomic architectures and spatial patterns of divergence. We sampled and phenotyped snails from seven replicate hybrid zones on the Swedish west coast and genotyped them for thousands of single nucleotide polymorphisms. Shell shape and size showed parallel clines across all zones. Many genomic regions showing steep clines and/or high differentiation were shared among hybrid zones, consistent with a common evolutionary history and extensive gene flow between zones, and supporting the importance of these regions for divergence. In particular, we found that several large putative inversions contribute to divergence in all locations. Additionally, we found evidence for consistent displacement of clines from the boulder–rock transition. Our results demonstrate patterns of spatial variation that would not be accessible without continuous spatial sampling, a large genomic data set and replicate hybrid zones.publishedVersio

Evaluation of sequence alignments and oligonucleotide probes with respect to three-dimensional structure of ribosomal RNA using ARB software package

BACKGROUND: Availability of high-resolution RNA crystal structures for the 30S and 50S ribosomal subunits and the subsequent validation of comparative secondary structure models have prompted the biologists to use three-dimensional structure of ribosomal RNA (rRNA) for evaluating sequence alignments of rRNA genes. Furthermore, the secondary and tertiary structural features of rRNA are highly useful and successfully employed in designing rRNA targeted oligonucleotide probes intended for in situ hybridization experiments. RNA3D, a program to combine sequence alignment information with three-dimensional structure of rRNA was developed. Integration into ARB software package, which is used extensively by the scientific community for phylogenetic analysis and molecular probe designing, has substantially extended the functionality of ARB software suite with 3D environment. RESULTS: Three-dimensional structure of rRNA is visualized in OpenGL 3D environment with the abilities to change the display and overlay information onto the molecule, dynamically. Phylogenetic information derived from the multiple sequence alignments can be overlaid onto the molecule structure in a real time. Superimposition of both statistical and non-statistical sequence associated information onto the rRNA 3D structure can be done using customizable color scheme, which is also applied to a textual sequence alignment for reference. Oligonucleotide probes designed by ARB probe design tools can be mapped onto the 3D structure along with the probe accessibility models for evaluation with respect to secondary and tertiary structural conformations of rRNA. CONCLUSION: Visualization of three-dimensional structure of rRNA in an intuitive display provides the biologists with the greater possibilities to carry out structure based phylogenetic analysis. Coupled with secondary structure models of rRNA, RNA3D program aids in validating the sequence alignments of rRNA genes and evaluating probe target sites. Superimposition of the information derived from the multiple sequence alignment onto the molecule dynamically allows the researchers to observe any sequence inherited characteristics (phylogenetic information) in real-time environment. The extended ARB software package is made freely available for the scientific community via

Schule und das neue Medium Internet - nicht ohne Lehrerinnen und

In der Arbeit wurde den Fragen nachgegangen, warum die Beteiligung sowohl von Lehrerinnen als auch Schülerinnen beim Einsatz des Internet in der Schule so gering ist und wie dies geändert werden kann. Nach verschiedenen Vorerhebungen wie der Auswertung von Fragebögen einer Klasse 10 (Gymnasium) und einer Expertenrunde von Lehrkräften zur Einführung des Internet Analyse der Beiträge zweier ausgewählter Mailinglisten zum Internet in der Schule Untersuchung der Homepages von Gymnasien wurden 1344 Projektanträge, mit denen sich Schulen in NRW um Teilnahme bei Schulen ans Netz - Verständigung weltweit beworben haben, quantitativ ausgewertet. Dabei stellte sich eine extreme Ungleichverteilung von Frauen und Männern am Projekt sowie eine sehr dominante Beteiligung von Lehrkräften des mathematisch-naturwissenschaftlichen Fachbereichs heraus. Zur Begründung dieser "nackten", erklärungsbedürftigen Zahlen sollten ExpertInneninterviews geführt werden, was sich schnell als wenig ergiebig herausstellte. Statt dessen wurden narrativ episodische Interviews mit 10 Lehrerinnen und 20 Lehrern (die z. T. als ModeratorInnen tätig sind) geführt, wodurch Gründe für die geringe Beteiligung von Lehrerinnen und Schülerinnen sichtbar wurden. Die Interviews mit zwei Moderatorinnen und zwei Moderatoren wurden umfangreich ausgewertet und eine Typisierung unterschiedlicher LehrerInnenpersönlichkeiten im Umgang mit dem Internet vorgenommen. In der Arbeit kam eine Methodenkombination von quantitativen und qualitativen Verfahren zur Anwendung, um den Untersuchungsgegenstand aus unterschiedlichen Perspektiven ausleuchten zu können. Einige ausgewählte Beispiele aus den schulischen Aufgabenfeldern zeigen auf überzeugende Weise, dass es sehr wohl geeignete Projekte gibt, die zu angemessener Beteiligung von Mädchen führen. Dadurch konnten zu den oben aufgestellten Fragen detailliert Stellung bezogen werden. Als Ergebnis kann u.a. festgehalten werden: Die Beteiligung von Lehrerinnen und Schülerinnen ist bisher marginal. Die dem Internet aufgeschlossene (kleine) Gruppe der Lehrerinnen, gehört entgegen gängiger Klischees eher der Gruppe der älteren (mit erwachsenen Kindern) an. Durch die Auswertung der Interviews konnten plausible Gründe dafür gefunden werden. Die Beteiligung von Mädchen hängt stark von den Fächern ab, in denen das Internet als Medium eingesetzt wird: sind es gern gewählte Fächer wie z. B. Sprachen (u. U. auch Kurse, in denen sie die Mehrzahl der Teilnehmenden stellen), akzeptieren sie den Einsatz des neuen Mediums Internet eher als in anderen. Die Beteiligung und das Engagement von Schülerinnen als auch die Akzeptanz monoedukativer Kurse durch Mädchen und Jungen hängt ganz entscheidend von den Persönlichkeiten der beteiligten Lehrkräfte ab. Mädchen können beispielsweise durch ihre Vorliebe für Chatten an das Internet herangeführt werden. Die Verknüpfung des Internet mit Informatik, der oftmals anzutreffende synonyme Gebrauch der beiden Wörter und die vielfach vorherrschende Meinung, fundierte Kenntnisse in der Informatik seien für einen qualifizierten Einsatz des Internet notwendig, stellen eine kaum zu überwindende Hürde für viele Lehrkräfte dar. Der Schlüssel zum Computer- oder besser Medienraum ist einer der zentralen Punkte: einerseits halten ihn Informatiklehrer unter Verschluß, andererseits ist die Hemmschwelle von Lehrkräften anderer Fächer kaum überwindbar. Lehrerfort- und weiterbildung sind dringend notwendig und zwar sowohl für einen kompetenten Umgang mit dem neuen Medium Internet als auch zu geschlechtsspezifischen Aspekten bzgl. des Verhaltens von Mädchen und Jungen bei der Arbeit am Computer. Insgesamt wurde ein durch die enge Verbindung von Internet mit Informatik geprägter Prozess der schulischen Neu-Konstruktion von Geschlechterdifferenzen in einem Feld, das zunächst keine geschlechtstypischen Zuschreibungen aufwies, rekonstruiert. Daraus resultierend wurden Vorschläge unterbreitet, wie eine größere Beteiligung von Lehrerinnen und Schülerinnen erreicht werden kann. Es wurden pädagogische Konsequenzen und Empfehlungen für ihre verstärkte Einbindung in die schulische Arbeit mit dem Internet dargestellt

A developmentally descriptive method for quantifying shape in gastropod shells

The growth of snail shells can be described by simple mathematical rules. Variation in a few parameters can explain much of the diversity of shell shapes seen in nature. However, empirical studies of gastropod shell shape variation typically use geometric morphometric approaches, which do not capture this growth pattern. We have developed a way to infer a set of developmentally descriptive shape parameters based on three-dimensional logarithmic helicospiral growth and using landmarks from two-dimensional shell images as input. We demonstrate the utility of this approach, and compare it to the geometric morphometric approach, using a large set of Littorina saxatilis shells in which locally adapted populations differ in shape. Our method can be modified easily to make it applicable to a wide range of shell forms, which would allow for investigations of the similarities and differences between and within many different species of gastropods