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Search Results: 1 - 10 of 1516 matches for " Marko Rohlfs "
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Clash of kingdoms or why Drosophila larvae positively respond to fungal competitors
Marko Rohlfs
Frontiers in Zoology , 2005, DOI: 10.1186/1742-9994-2-2
Abstract: Based on laboratory experiments in which Drosophila larvae were offered the choice between fungal-infected and uninfected food patches, larvae significantly aggregated on patches containing young fungal colonies. Grouping behaviour was also visible when larvae were offered only fungal-infected or only uninfected patches; however, larval aggregation was less strong under these conditions than in a heterogeneous environment (infected and uninfected patches).Because filamentous fungi can be deadly competitors for insect larvae on ephemeral resources, social attraction of Drosophila larvae to fungal-infected sites leading to suppression of mould growth may reflect an adaptive behavioural response that increases insect larval fitness and can thus be discussed as an anti-competitor behaviour. These observations support the hypothesis that adverse environmental conditions operate in favour of social behaviour. In a search for the underlying mechanisms of communal behaviour in Drosophila, this study highlights the necessity of investigating the role of inter-kingdom competition as a potential driving force in the evolution of spatial behaviour in insects.A common idea in animal ecology is that adverse or stressful environmental conditions facilitate the evolution of social behaviour [1]. The formation of groups across a huge number of animal taxa is thus considered to have broad implications for the benefit of individuals, including mate finding, the efficient location and use of resources, thermoregulation, energetic benefits and defence against natural enemies or competitors [2,3]. Basic proximate prerequisites for communal behaviour are cues indicating the location of conspecifics and the ability to receive and process information regarding these cues, which in turn induce inter-individual attraction [3]. Because the costs and benefits of communal behaviour typically vary with environmental conditions, the degree to which individuals are mutually attracted is regulated b
Experimental evolution of defense against a competitive mold confers reduced sensitivity to fungal toxins but no increased resistance in Drosophila larvae
Monika Trienens, Marko Rohlfs
BMC Evolutionary Biology , 2011, DOI: 10.1186/1471-2148-11-206
Abstract: To examine the relationship between the ability to survive competition with toxic fungi, sensitivity to fungal toxins and resistance, we created fungal-selected (FS) replicated insect lines by exposing Drosophila melanogaster larvae to the fungal competitor Aspergillus nidulans over 26 insect generations. Compared to unselected control lines (UC), larvae from the FS lines had higher survival rates in the presence of A. nidulans indicating selection for increased protection against the fungal antagonist. In line with our expectation, FS lines were less susceptible to the A. nidulans mycotoxin Sterigmatocystin. Of particular interest is that evolved protection against A. nidulans and Sterigmatocytin was not correlated with increased insect survival in the presence of other fungi and mycotoxins. We found no evidence that FS lines were better at suppressing the expansion of fungal colonies but observed a trend towards a less detrimental effect of FS larvae on fungal growth.Antagonistic but non-pathogenic fungi favor insect variants better protected against the fungal chemical arsenal. This highlights the often proposed but experimentally underexplored importance of secondary metabolites in driving animal-fungus interactions. Instead of enhanced resistance, insect larvae tend to have evolved increased tolerance of the fungal competitor. Future studies should examine whether sensitivity to allelopathic microbial metabolites drives a trade-off between resistance and tolerance in insect external defense.The fungal kingdom contains an underexplored diversity of organisms occurring in almost all terrestrial, marine and freshwater ecosystems [1]. Because fungi constitute an important food source for animals or act as serious competitors of them [2,3] they are assumed to have evolved defense strategies employing toxic or deterrent secondary chemicals [4-6]. Animals, in turn, may be selected for counter-adaptations that render fungal toxins less detrimental [7], thus placing a h
Induced Fungal Resistance to Insect Grazing: Reciprocal Fitness Consequences and Fungal Gene Expression in the Drosophila-Aspergillus Model System
Silvia Caballero Ortiz, Monika Trienens, Marko Rohlfs
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0074951
Abstract: Background Fungi are key dietary resources for many animals. Fungi, in consequence, have evolved sophisticated physical and chemical defences for repelling and impairing fungivores. Expression of such defences may entail costs, requiring diversion of energy and nutrients away from fungal growth and reproduction. Inducible resistance that is mounted after attack by fungivores may allow fungi to circumvent the potential costs of defence when not needed. However, no information exists on whether fungi display inducible resistance. We combined organism and fungal gene expression approaches to investigate whether fungivory induces resistance in fungi. Methodology/Principal Findings Here we show that grazing by larval fruit flies, Drosophila melanogaster, induces resistance in the filamentous mould, Aspergillus nidulans, to subsequent feeding by larvae of the same insect. Larval grazing triggered the expression of various putative fungal resistance genes, including the secondary metabolite master regulator gene laeA. Compared to the severe pathological effects of wild type A.?nidulans, which led to 100% insect mortality, larval feeding on a laeA loss-of-function mutant resulted in normal insect development. Whereas the wild type fungus recovered from larval grazing, larvae eradicated the chemically deficient mutant. In contrast, mutualistic dietary yeast, Saccharomyces cerevisiae, reached higher population densities when exposed to Drosophila larval feeding. Conclusions/Significance Our study presents novel evidence that insect grazing is capable of inducing resistance to further grazing in a filamentous fungus. This phenotypic shift in resistance to fungivory is accompanied by changes in the expression of genes involved in signal transduction, epigenetic regulation and secondary metabolite biosynthesis pathways. Depending on reciprocal insect-fungus fitness consequences, fungi may be selected for inducible resistance to maintain high fitness in fungivore-rich habitats. Induced fungal defence responses thus need to be included if we wish to have a complete conception of animal-fungus co-evolution, fungal gene regulation, and multitrophic interactions.
Aspergillus nidulans Synthesize Insect Juvenile Hormones upon Expression of a Heterologous Regulatory Protein and in Response to Grazing by Drosophila melanogaster Larvae
Morten Thrane Nielsen, Marie Louise Klejnstrup, Marko Rohlfs, Diana Chinyere Anyaogu, Jakob Bl?sbjerg Nielsen, Charlotte Held Gotfredsen, Mikael R?rdam Andersen, Bjarne Gram Hansen, Uffe Hasbro Mortensen, Thomas Ostenfeld Larsen
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073369
Abstract: Secondary metabolites are known to serve a wide range of specialized functions including communication, developmental control and defense. Genome sequencing of several fungal model species revealed that the majority of predicted secondary metabolite related genes are silent in laboratory strains, indicating that fungal secondary metabolites remain an underexplored resource of bioactive molecules. In this study, we combine heterologous expression of regulatory proteins in Aspergillus nidulans with systematic variation of growth conditions and observe induced synthesis of insect juvenile hormone-III and methyl farnesoate. Both compounds are sesquiterpenes belonging to the juvenile hormone class. Juvenile hormones regulate developmental and metabolic processes in insects and crustaceans, but have not previously been reported as fungal metabolites. We found that feeding by Drosophila melanogaster larvae induced synthesis of juvenile hormone in A. nidulans indicating a possible role of juvenile hormone biosynthesis in affecting fungal-insect antagonisms.
Shallow Axi-symmetric Bimetallic Shell as a Switching Element in a Non-Homogenous Temperature Field  [PDF]
Marko Jakomin
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.32015
Abstract: In this contribution we discuss the stability of thin, axi-symmetric, shallow bimetallic shells in a non-homo- geneous temperature field. The presented model with a mathematical description of the geometry of the system, displacements, stresses and thermoelastic deformations on the shell, is based on the theory of the third order, which takes into account not only the equilibrium of forces on a deformed body but also the non-linear terms of the strain tensor. The equations are based on the large displacements theory. As an example, we pre- sent the results for a bimetallic shell of parabolic shape, which has a temperature point load at the apex. We translated the boundary-value problem with the shooting method into saving the initial-value problem. We calculate the snap-through of the system numerically by the Runge-Kutta fourth order method.
On equivariant Euler-Poincaré characteristic in sheaf cohomology
Steffen Kionke,Jürgen Rohlfs
Mathematics , 2013,
Abstract: Let X be a topological Hausdorff space together with a continuous action of a finite group G. Let R be the ring of integers of a number field F. Let E be a G-sheaf of flat R-modules over X and let $\Phi$ be a G-stable paracompactifying family of supports on X. We show that under some natural cohomological finiteness conditions the Lefschetz number of the action of g in G on the cohomology $H_\Phi(X,E) \otimes_{R} F$ equals the Lefschetz number of the g-action on $H_\Phi(X^g, E_{|X^g}) \otimes_{R} F$, where $X^g$ is the set of fixed points of g in X. More generally, the class $\sum_j (-1)^j [H^j_\Phi (X,E) \otimes_R F]$ in the character group equals a sum of representations induced from irreducible F-rational representations $V_\lambda$ of $H$ where $H$ runs in the set of G-conjugacy classes of subgroups of G. The integral coefficients $m_\lambda$ in this sum are explicitly determined.
Actuar contra la violencia de género: un reto para la salud pública
Rohlfs Izabella,Valls-Llobet Carme
Gaceta Sanitaria , 2003,
Abstract:
Accuracy of the WKB approximation: the case of general quartic potential
Marko Vranicar,Marko Robnik
Physics , 2000, DOI: 10.1143/PTPS.139.214
Abstract: We analyse the accuracy of the approximate WKB quantization for the case of general one-dimensional quartic potential. In particular, we are interested in the validity of semiclassically predicted energy eigenvalues when approaching the limit $E\to \infty$, and in the accuracy of low lying energy levels below the potential barrier in the case of generally asymmetric double-well quartic potential. In the latter case, using the standard WKB quantization an unnatural localization of eigenstates due to the negligence of tunneling is implied and thus the validity of semiclassics is uncertain. In all computations the higher order corrections to the leading semiclassical approximation are included using the complex contour integration technique. We show that these corrections can improve accuracy of semiclassical approximation greatly by many orders of magnitude.
Familial Identification: Population Structure and Relationship Distinguishability
Rori V. Rohlfs ,Stephanie Malia Fullerton,Bruce S. Weir
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002469
Abstract: With the expansion of offender/arrestee DNA profile databases, genetic forensic identification has become commonplace in the United States criminal justice system. Implementation of familial searching has been proposed to extend forensic identification to family members of individuals with profiles in offender/arrestee DNA databases. In familial searching, a partial genetic profile match between a database entrant and a crime scene sample is used to implicate genetic relatives of the database entrant as potential sources of the crime scene sample. In addition to concerns regarding civil liberties, familial searching poses unanswered statistical questions. In this study, we define confidence intervals on estimated likelihood ratios for familial identification. Using these confidence intervals, we consider familial searching in a structured population. We show that relatives and unrelated individuals from population samples with lower gene diversity over the loci considered are less distinguishable. We also consider cases where the most appropriate population sample for individuals considered is unknown. We find that as a less appropriate population sample, and thus allele frequency distribution, is assumed, relatives and unrelated individuals become more difficult to distinguish. In addition, we show that relationship distinguishability increases with the number of markers considered, but decreases for more distant genetic familial relationships. All of these results indicate that caution is warranted in the application of familial searching in structured populations, such as in the United States.
Desigualdades en salud según la clase social en las mujeres: ?Cómo influye el tipo de medida de la clase social?
Borrell,Carme; Rohlfs,Izabella; Artazcoz,Lucía; Muntaner,Carles;
Gaceta Sanitaria , 2004, DOI: 10.1590/S0213-91112004000800010
Abstract: classical theories of social stratification share the assumption that the family is the unit of stratification, using the man's occupation as a measure of social class. these theories were criticized by feminism, which claimed that women were not visible in class analysis. the present article aims firstly to review measurement of women's social class, secondly to review studies on the impact of different measures of social class on inequalities in health among women, and thirdly to illustrate the differences among alternative measures, using data from the barcelona health interview survey 2000 as an example. there are few studies analyzing inequalities in health among women that take into account several measures of social class; most studies have been performed in the united kingdom, although some studies have been conducted in other countries. typically, these studies compare several social class indicators: the ?conventional social class? measure, which uses the husband's occupation or tal of the head of household (a household measure); the ?individual social class? measure, which uses women's occupation, and the ?dominant social class? measure, which allocates an individual the highest social class within a household (also a household measure). the impact of the various measures on inequalities in health varies according to the study performed, but is usually greater with the conventional and dominant approaches. data from the health interview survey of barcelona 2000 show the existence of inequalities in health using these three approaches, with varied impact according to the health indicators used and women's characteristics. the ?dominant social class? measure has several advantages: it is gender-blind and is not sexist. when the dominant social class is a less privileged class (i.e. manual laborer) it means that both partners have an occupation equal to or lower than this measure. finally, this indicator is easily obtained.
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