Host specificity and adaptation of Schistocephalus to its stickleback hosts

Parasites are a major evolutionary driving force. They impose a selection factor not only on individual hosts, but also on whole populations altering natural and sexual selection. The coevolution between hosts and parasites leads to an evolutionary arms race, where hosts evolve towards higher resistance and parasites towards increased exploitation. Parasites have evolved many different adaptations to increase their potential to successfully infect and exploit their hosts. A parasite with a multi-host life cycle may use the different hosts for different purposes and must adapt to different conditions at each stage. All adaptations should ultimately increase the parasite’s fitness: through higher growth and higher rates of transmission and reproduction. The work of my thesis examines the adaptations of parasites, specifically tapeworms of the genus Schistocephalus (S. solidus and S. pungitii), to their host organisms: three-spined sticklebacks (Gasterosteus aculeatus) and nine-spined sticklebacks (Pungitius pungitius). Schistocephalus has long been known to be very specific regarding the second intermediate (stickleback) host, which indicates close coevolution of these species. In chapter I of this thesis I examined this high degree of host specificity by experimentally exposing sticklebacks to either their specific or the incompatible parasite species and monitoring the infection process histologically. This could show that the incompatible parasite species can still establish in the stickleback, but is eliminated within the first two weeks after infection. I also tested, whether the known immune manipulation by S. solidus in three-spined sticklebacks allows a superinfection with the incompatible parasite in sequential exposures, but the results indicate that this is not possible. In the second experiment I hybridized two different Schistocephalus species (S. solidus and S. pungitii) in an in vitro breeding system and measured fitness relevant traits throughout the whole life cycle. I could show that the two species are capable of producing viable hybrid offspring, even though the outcrossing and hatching rates are lower in these pairings than in the parental species. Nevertheless, the hybrids exhibit no decreased infection rate in the first and second intermediate hosts and surprisingly show an extended host range, as they are able to infect both stickleback species, while the parental lines can only infect their specific host. This is surprising, as natural hybrids between S. solidus and S. pungitii have not yet been observed and molecular data indicates a deep lineage divergence and no gene flow. In the next part of this thesis I therefore tested, if prezygotic barriers prevent hybridization in natural populations. The results suggest that the species can hybridize in natural hosts, there are no barriers to hybridization in sympatric populations and the parasites even prefer parasites of the different species over conspecifics in a mate choice experiment. In summary, these results indicate that host specificity in Schistocephalus is presumably maintained in this system due to the specific reaction of the stickleback’s immune system, even though the advantages and the mechanisms are still unclear. It is possible that the high degree of host specificity is important for successful long term interactions with the stickleback immune system, even though our results indicate no trade-off at this level. The ability of a parasite to successfully establish and exploit a host is also determined by parasite virulence, which depends on many factors that also include intraspecific interactions among co-infecting parasites. In the last part of this thesis, I investigated the plasticity of individual parasite virulence using experimental co-infections with two different strains of S. solidus that differ in virulence within three-spined sticklebacks. This showed that intraspecific interactions alter individual virulence in S. solidus, where the less virulent parasite benefits from the presence of a high-virulent conspecific and the high-virulent parasite exhibits reduced virulence in heterologous co-infections. This thesis demonstrates that these parasites use numerous and elaborate approaches to adapt to their host. Furthermore, the outcome of a parasitic infection is dependent on the close coevolution between parasitic exploitation strategies and host defenses, and finally, these interactions become even more complex with multiple infections.Table of Contents Summary .............................................................................................................................. 1 Zusammenfassung................................................................................................................ 3 Introduction .......................................................................................................................... 7 Thesis outline ..................................................................................................................... 16 Chapter I............................................................................................................................. 19 Chapter II ........................................................................................................................... 33 Chapter III .......................................................................................................................... 53 Chapter IV .......................................................................................................................... 67 Conclusion & Perspectives ................................................................................................ 87 Author contributions .......................................................................................................... 93 Acknowledgements ............................................................................................................ 95 References .......................................................................................................................... 97 List of publications .......................................................................................................... 117 Eidesstattliche Erklärung ................................................................................................. 119 Appendix .......................................................................................................................... 12

Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach

A quantum transport model incorporating spin scattering processes is presented using the non-equilibrium Green's function (NEGF) formalism within the self-consistent Born approximation. This model offers a unified approach by capturing the spin-flip scattering and the quantum effects simultaneously. A numerical implementation of the model is illustrated for magnetic tunnel junction devices with embedded magnetic impurity layers. The results are compared with experimental data, revealing the underlying physics of the coherent and incoherent transport regimes. It is shown that small variations in magnetic impurity spin-states/concentrations could cause large deviations in junction magnetoresistances.Comment: NEGF Formalism, Spin Dephasing, Magnetic Tunnel Junctions, Magnetoresistanc

Small quantum networks operating as quantum thermodynamic machines

We show that a 3-qubit system as studied for quantum information purposes can alternatively be used as a thermodynamic machine when driven in finite time and interfaced between two split baths. The spins are arranged in a chain where the working spin in the middle exercises Carnot cycles the area of which defines the exchanged work. The cycle orientation (sign of the exchanged work) flips as the difference of bath temperatures goes through a critical value.Comment: RevTeX, 4 pages, 7 figures. Replaced by version accepted for publication in EP

Ab-initio study of BaTiO3 surfaces

We have carried out first-principles total-energy calculations of (001) surfaces of the tetragonal and cubic phases of BaTiO3. Both BaO-terminated (type I) and TiO2-terminated (type II) surfaces are considered, and the atomic configurations have been fully relaxed. We found no deep-gap surface states for any of the surfaces, in agreement with previous theoretical studies. However, the gap is reduced for the type-II surface, especially in the cubic phase. The surface relaxation energies are found to be substantial, i.e., many times larger than the bulk ferroelectric well depth. Nevertheless, the influence of the surface upon the ferroelectric order parameter is modest; we find only a small enhancement of the ferroelectricity near the surface.Comment: 8 pages, two-column style with 4 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#pad_sur

Overconfidence is universal? Elicitation of genuine overconfidence (EGO) procedure reveals systematic differences across domain, task knowledge, and incentives in four populations

Overconfidence is sometimes assumed to be a human universal, but there remains a dearth of data systematically measuring overconfidence across populations and contexts. Moreover, cross-cultural experiments often fail to distinguish between placement and precision and worse still, often compare population-mean placement estimates rather than individual performance subtracted from placement. Here we introduce a procedure for concurrently capturing both placement and precision at an individual level based on individual performance: The Elicitation of Genuine Overconfidence (EGO) procedure. We conducted experiments using the EGO procedure, manipulating domain, task knowledge, and incentives across four populations—Japanese, Hong Kong Chinese, Euro Canadians, and East Asian Canadians. We find that previous measures of population-level overconfidence may have been misleading; rather than universal, overconfidence is highly context dependent. Our results reveal cross-cultural differences in sensitivity to incentives and differences in overconfidence strategies, with underconfidence, accuracy, and overconfidence. Comparing sexes, we find inconsistent results for overplacement, but that males are consistently more confident in their placement. These findings have implications for our understanding of the adaptive value of overconfidence and its role in explaining population-level and individual-level differences in economic and psychological behavior

Tests of silicon sensors for the CMS pixel detector

The tracking system of the CMS experiment, currently under construction at the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland), will include a silicon pixel detector providing three spacial measurements in its final configuration for tracks produced in high energy pp collisions. In this paper we present the results of test beam measurements performed at CERN on irradiated silicon pixel sensors. Lorentz angle and charge collection efficiency were measured for two sensor designs and at various bias voltages.Comment: Talk presented at 6th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, September 29-October 1, 2003, Firenze, Italy. Proceedings will be published in Nuclear Instr. & Methods in Phys. Research, Section

A combinatorial approach to knot recognition

This is a report on our ongoing research on a combinatorial approach to knot recognition, using coloring of knots by certain algebraic objects called quandles. The aim of the paper is to summarize the mathematical theory of knot coloring in a compact, accessible manner, and to show how to use it for computational purposes. In particular, we address how to determine colorability of a knot, and propose to use SAT solving to search for colorings. The computational complexity of the problem, both in theory and in our implementation, is discussed. In the last part, we explain how coloring can be utilized in knot recognition

Nest use is influenced by the positions of nests and drinkers in aviaries

The influence of the nest location and the placement of nipple drinkers on nest use by laying hens in a commercial aviary was assessed. Twenty pens in a laying hen house were equipped with the same commercial aviary system, but the pens differed in the nest location and the placement of nipple drinkers. Nests were placed along the walls in 10 pens, and nipple drinkers were installed in front of the nests in 5 of these pens. The other 10 pens were equipped with nests placed on a tier within the aviary (integrated nests). Nipple drinkers were installed in front of the nests in 5 of these pens. A total of 225 Lohmann Selected Leghorns were housed per pen. The hens were offered 4 nests per pen: 2 facing the service corridor of the laying hen house and 2 facing the outdoor area. The numbers of nest eggs and mislaid eggs were counted daily per pen. At 25, 36, and 43 wk of age, the nest platforms were videotaped and the behavior of laying hens in front of the nests was analyzed. The nest location affected the stationary and locomotive behaviors in front of the nests. Hens in front of the integrated nests and the nests with drinkers displayed more stationary behaviors than hens in front of wall-placed nests or nests without drinkers. No difference in the number of nest eggs could be detected, but the integration of the nests inside the aviary led to a more even distribution of hens while nest searching. In the pens with wall-placed nests, significantly more hens laid eggs in the nests at the wall near the service corridor than at the wall near the outdoor area. Due to this imbalance, crowding in front of the preferred nests occurred and pushing and agonistic interactions on the nest platforms were significantly more frequent. Placement of nipple drinkers in front of nests had no effect on the number of eggs laid in those nest

Exchange bias and interface electronic structure in Ni/Co3O4(011)

A detailed study of the exchange bias effect and the interfacial electronic structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are observed at low temperatures, and the exchange bias effect persists to temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to ~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy measurements as a function of Ni thickness show that Co reduction and Ni oxidation occur over an extended interfacial region. We conclude that the exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4 systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at the interface.Comment: 8 pages, 6 figures. Accepted for publication in Physical Review B