On the Einstein-Vlasov system with cosmological constant

Das Einstein-Vlasov-System beschreibt die Zeitentwicklung stossfreier Materie im Rahmen der Allgemeinen Relativitätstheorie. Ziel dieser Arbeit ist es, möglichst viele Informationen zu bekommen über globale Lösungen des Anfangswertproblems für das Einstein-Vlasov-System mit kosmologischer Konstante Lambda und sphärischer, ebener oder hyperbolischer Symmetrie, geschrieben in Flächenkoordinaten. Die vorliegende Untersuchung befasst sich mit Raumzeiten, die eine kompakte Cauchy-Hyperfläche besitzen, und in diesem Fall werden Daten auf einer kompakten dreidimensionalen Mannigfaltigkeit gegeben. Die Ergebnisse von G. Rein über lokale Existenz und Fortsetzungskriterien für Raumzeiten mit Lambda=0 werden auf den Fall mit Lambda ungleich Null erweitert. Es wird ausserdem die Lösbarkeit der Zwangsbedingungen bewiesen, die durch die Anfangsdaten erfüllt werden müssen. Es wird gezeigt dass im Fall Lambda kleiner Null keine in der Zukunft globale Lösung existieren kann, so dass die Untersuchung in der expandierenden Richtung sich auf den Fall Lambda grösser Null beschränkt. Mit der Annahme ebener (k=0) oder hyperbolischer (k=-1) Symmetrie und Lambda grösser Null, wird gezeigt, dass der Flächenradius in der Zukunft gegen unendlich strebt so dass globale Existenz in der Zukunft gilt, dass die Raumzeiten in der Zukunft geodätisch vollständig sind, und dass die Expansion zu späten Zeiten isotrop und exponentiell wird. Dadurch wird in dieser Klasse von Raumzeiten eine Form einer Aussage bewiesen, die als "cosmic no hair theorem" bezeichnet wird. Entsprechende Ergebnisse werden auch im sphärisch symmetrischen Fall (k=1) bewiesen, vorausgesetzt dass die Anfangszeit hinreichend gross ist. Ausserdem wird das Verhalten des Energie-Impuls-Tensors zu späten Zeiten analysiert. Zusätzlich wird globale Existenz in der Vergangenheit bewiesen für generische Anfangsdaten wenn Lambda kleiner gleich Null und k grösser gleich Null. Ausserdem werden einige bekannte Ergebnisse verallgemeinert in dem die Existenz bis t=0 für kleine Daten wenn Lambda kleiner Null und k=-1 oder wenn Lambda grösser Null bewiesen wird. In diesem Fall wird bewiesen dass eine Krümmungsinvariante, der Kretschmann-Skalar, für t gegen Null explodiert, so dass es eine Singularität bei t=0 gibt. Anschliessend wird die Natur dieser Anfangssingularität analysiert und es wird gezeigt, dass das asymptotische Verhalten dem einer Kasner-Lösung ähnelt.The Einstein-Vlasov system governs the time evolution of a self-gravitating collisionless gas in the context of general relativity. The aim of this thesis is to obtain as much information as possible about global solutions of the initial value problem for the Einstein-Vlasov system with cosmological constant and spherical, plane or hyperbolic symmetry, written in areal coordinates. Our investigation is concerned with the spacetimes possessing a compact Cauchy hypersurface, in this case the data are given on a compact 3-manifold. The results on the local existence and continuation criteria obtained by G. Rein for the Einstein-Vlasov system with vanishing cosmological constant are extended to the case with a non-zero cosmological constant. We also prove the solvability of the constraint problem on the initial data. We show that there is no global solution in the future when the cosmological constant is negative so that the study in the expanding direction deals only with the positive cosmological constant case. Under the assumption of plane (k=0) or hyperbolic (k=-1) symmetry and that the cosmological constant Lambda is positive we prove that the area radius goes to infinity and so global existence in the future time direction is shown, the spacetimes are future geodesically complete, and the expansion becomes isotropic and exponential at late times. This proves a form of the so-called cosmic no-hair theorem in this class of spacetimes. These results are also proved in the spherically symmetric case (k=1) provided that the initial time is sufficiently large. Furthermore we analyze the behaviour of the energy-momentum tensor at late times. In addition, in the past time direction we prove global existence for generic data if Lambda is non-positive and k is non-negative. Besides this we generalize some known results in the literature by proving existence up to t=0 for small data in the cases Lambda negative, k=-1 and Lambda positive, by proving that the curvature invariant called Kretschmann scalar blows up as t tends to zero so that there is a singularity at t=0. Furthermore we analyze the nature of this initial singularity and also show that the asymptotics is Kasner-like at early times

Feeding habits of culicine mosquitoes in the Cameroon lowland forests based on stable isotopes and blood meal analyses

Mosquito blood feeding behavior is a very significant component of pathogen transmission and determinant of disease epidemiology. Yet, knowledge of foraging ecology of mosquitoes often depends on the presence of undigested blood in the mosquito mid gut. Approximately 36 h after feeding, the blood meal is sufficiently digested to make identification by molecular techniques difficult, leaving a very narrow window in which these methods can be utilized. Here, we investigated the feeding habits of wild caught culicine mosquitoes from four genera, Aedes, Anopheles, Coquillettidia and Mansonia of the lowland rainforests of Cameroon based on the isotopic ratios of nitrogen (δ C appearing to be the best element to differentiate between mosquito species that fed on different host species. Isotopic analyses show that the different mosquito genera may be separated based on their diets, suggesting that linking stable isotope-based assays and DNA analysis may be a powerful new tool to investigate mosquito feeding ecology and the dynamics of vector-borne pathogens

Divergent seed dispersal outcomes: Interactions between seed, disperser, and forest traits

Animals disperse seeds in various ways that affect seed deposition sites and seed survival, ultimately shaping plant species distribution, community composition, and ecosystem structure. Some animal species can disperse seeds through multiple pathways (e.g., defecation, regurgitation, epizoochory), each likely producing distinct seed dispersal outcomes. We studied how seed traits (size and toughness) interact with disperser species to influence seed dispersal pathway and how this ultimately shapes the proportion of seeds deposited in various habitat types. We focused on three frugivorous species of duikers (African forest antelopes) in the Dja Faunal Reserve, a tropical rainforest in southern Cameroon. Duikers can both defecate and regurgitate seeds, the latter predominantly occurring during rumination at their bedding sites (or "nests"). We located duiker nests and dungs along 18 linear 1-km-transects to assess: (1) how seed traits affect the likelihood of dispersal via defecation versus regurgitation, (2) if defecated versus regurgitated seeds are deposited at different rates in different forest types (assessed by indigenous Baka), microhabitats, and forest structural attributes (measured by drone lidar), and (3) if these differ between three duiker species that vary in size and diel activity patterns. We found that duikers predominantly defecated small seeds (<3 mm length) and regurgitated larger and tougher seeds (>10 mm length), the latter including 25 different plant species. The three duiker species varied in their nesting habits, with nocturnal bay duikers (Cephalophus dorsalis) nesting in dense understory vegetation at proportions 3-4 times higher than Peter's and yellow-backed duikers (Cephalophus callipygus and Cephalophus silvicultor). As a result, bay duikers deposited larger regurgitated seeds at a higher rate in habitats with denser understory where lianas and palms predominate and near fallen trees. This directed regurgitation seed deposition likely plays an important and unique role in forest succession and structure. This study highlights the importance of ungulate seed dispersal by regurgitation, a vastly understudied process that could impact many ecosystems given the prevalence of ruminating ungulates worldwide

Locating giant ground pangolins (Smutsia gigantea) using camera traps on burrows in the Dja Biosphere Reserve, Cameroon

Published online: 15 Jan 2018Giant ground pangolins (Smutsia gigantea) are poorly known and difficult to study due to their nocturnal and burrowing habits. Here, we test the efficacy of using camera traps on potentially active burrows identified by local Ba'Aka guides to rapidly locate giant ground pangolins in the wild for subsequent observation and tagging for telemetry studies. We deployed nine cameras on potential giant ground pangolin burrows in the Dja Biosphere Reserve, Cameroon. One camera photographed an adult male giant ground pangolin using a burrow within 2 days of camera deployment. The pangolin used the same burrow several times over a 25-day period and possible scent-marking behavior was recorded

The global antigenic diversity of swine influenza A viruses.

Swine influenza presents a substantial disease burden for pig populations worldwide and poses a potential pandemic threat to humans. There is considerable diversity in both H1 and H3 influenza viruses circulating in swine due to the frequent introductions of viruses from humans and birds coupled with geographic segregation of global swine populations. Much of this diversity is characterized genetically but the antigenic diversity of these viruses is poorly understood. Critically, the antigenic diversity shapes the risk profile of swine influenza viruses in terms of their epizootic and pandemic potential. Here, using the most comprehensive set of swine influenza virus antigenic data compiled to date, we quantify the antigenic diversity of swine influenza viruses on a multi-continental scale. The substantial antigenic diversity of recently circulating viruses in different parts of the world adds complexity to the risk profiles for the movement of swine and the potential for swine-derived infections in humans.Medical Research Council Fellowship MR/K021885/1 (JF

Coquillettidia (Culicidae, Diptera) mosquitoes are natural vectors of avian malaria in Africa

<p>Abstract</p> <p>Background</p> <p>The mosquito vectors of <it>Plasmodium </it>spp. have largely been overlooked in studies of ecology and evolution of avian malaria and other vertebrates in wildlife.</p> <p>Methods</p> <p><it>Plasmodium </it>DNA from wild-caught <it>Coquillettidia </it>spp. collected from lowland forests in Cameroon was isolated and sequenced using nested PCR. Female <it>Coquillettidia aurites </it>were also dissected and salivary glands were isolated and microscopically examined for the presence of sporozoites.</p> <p>Results</p> <p>In total, 33% (85/256) of mosquito pools tested positive for avian <it>Plasmodium </it>spp., harbouring at least eight distinct parasite lineages. Sporozoites of <it>Plasmodium </it>spp. were recorded in salivary glands of <it>C. aurites </it>supporting the PCR data that the parasites complete development in these mosquitoes. Results suggest <it>C. aurites</it>, <it>Coquillettidia pseudoconopas </it>and <it>Coquillettidia metallica </it>as new and important vectors of avian malaria in Africa. All parasite lineages recovered clustered with parasites formerly identified from several bird species and suggest the vectors capability of infecting birds from different families.</p> <p>Conclusion</p> <p>Identifying the major vectors of avian <it>Plasmodium </it>spp. will assist in understanding the epizootiology of avian malaria, including differences in this disease distribution between pristine and disturbed landscapes.</p

Finding the appropriate variables to model the distribution of vector-borne parasites with different environmental preferences: climate is not enough

Understanding how environmental variation influences the distribution of parasite diversity is critical if we are to anticipate disease emergence risks associated with global change. However, choosing the relevant variables for modelling current and future parasite distributions may be difficult: candidate predictors are many, and they seldom are statistically independent. This problem often leads to simplistic models of current and projected future parasite distributions, with climatic variables prioritized over potentially important landscape features or host population attributes. We studied avian blood parasites of the genera Plasmodium, Haemoproteus and Leucocytozoon (which are viewed as potential emergent pathogens) in 37 Iberian blackcap Sylvia atricapilla populations. We used Partial Least Squares regression to assess the relative importance of a wide array of putative determinants of variation in the diversity of these parasites, including climate, landscape features and host population migration. Both prevalence and richness of parasites were predominantly related to climate (an effect which was primarily, but not exclusively driven by variation in temperature), but landscape features and host migration also explained variation in parasite diversity. Remarkably, different models emerged for each parasite genus, although all parasites were studied in the same host species. Our results show that parasite distribution models, which are usually based on climatic variables alone, improve by including other types of predictors. Moreover, closely related parasites may show different relationships to the same environmental influences (both in magnitude and direction). Thus a model used to develop one parasite distribution can probably not be applied identically even to the most similar host-parasite systems

Global migration of influenza A viruses in swine

The complex and unresolved evolutionary origins of the 2009 H1N1 influenza pandemic exposed major gaps in our knowledge of the global spatial ecology and evolution of influenza A viruses in swine (swIAVs). Here we undertake an expansive phylogenetic analysis of swIAV sequence data and demonstrate that the global live swine trade strongly predicts the spatial dissemination of swIAVs, with Europe and North America acting as sources of viruses in Asian countries. In contrast, China has the world's largest swine population but is not a major exporter of live swine, and is not an important source of swIAVs in neighbouring Asian countries or globally. A meta-population simulation model incorporating trade data predicts that the global ecology of swIAVs is more complex than previously thought, and the United States and China's large swine populations are unlikely to be representative of swIAV diversity in their respective geographic regions, requiring independent surveillance efforts throughout Latin America and Asia.status: publishe

On the study of the transmission networks of blood parasites from SW Spain: diversity of avian haemosporidians in the biting midge Culicoides circumscriptus and wild birds

BACKGROUND: Blood-sucking flying insects play a key role in the transmission of pathogens of vector-borne diseases. However, at least for the case of avian malaria parasites, the vast majority of studies focus on the interaction between parasites and vertebrate hosts, but there is a lack of information regarding the interaction between the parasites and the insect vectors. Here, we identified the presence of malaria and malaria-like parasite lineages harbored by the potential vector Culicoides circumscriptus (Kieffer). Also, we identified some nodes of the transmission network connecting parasite lineages, potential insect vectors and avian hosts by comparing Haemoproteus and Plasmodium lineages isolated from insects with those infecting wild birds in this and previous studies. METHODS: Using a molecular approach, we analysed the presence of blood parasites in a total of 97 biting midges trapped in the Doñana National Park (SW Spain) and surrounding areas. Also, 123 blood samples from 11 bird species were analyzed for the presence of blood parasite infections. Blood parasites Haemoproteus and Plasmodium were identified by amplification of a 478 bp fragment of the mitochondrial cytochrome b gen. RESULTS: Thirteen biting midges harboured blood parasites including six Haemoproteus and two Plasmodium lineages, supporting the potential role of these insects on parasite transmission. Moreover, ten (8.1%) birds carried blood parasites. Seven Plasmodium and one Haemoproteus lineages were isolated from birds. Overall, six new Haemoproteus lineages were described in this study. Also, we identified the transmission networks of some blood parasites. Two Haemoproteus lineages, hCIRCUM03 and GAGLA03, were identical to those isolated from Corvus monedula in southern Spain and Garrulus glandarius in Bulgaria, respectively. Furthermore, the new Haemoproteus lineage hCIRCUM05 showed a 99% similarity with a lineage found infecting captive penguins in Japan. CONCLUSIONS: The comparison of the parasite lineages isolated in this study with those previously found infecting birds allowed us to identify some potential nodes in the transmission network of avian blood parasite lineages. These results highlight the complexity of the transmission networks of blood parasites in the wild that may involve a high diversity of susceptible birds and insect vectors

Host Specialization and Dispersal in Avian Haemosporidians

In order to be able to understand the ecological and evolutionary processes involved in the emergence of infectious diseases, one needs to comprehend how parasites arrive at new geographical areas and how they manage to maintain viable populations and even expand their ranges. We discuss host specificity in avian haemosporidians and how encounter and compatibility filters affect the dispersal of avian haemosporidians, and how these filters affect avian haemosporidian assemblages at different spatial and evolutionary scales. There are at least three important barriers to the dispersal of avian haemosporidians: (i) geographic barriers, (ii) environmental barriers, and (iii) interspecies barriers. In this chapter, we discuss the factors involved in these barriers and their effects on the structure of avian haemosporidian assemblages. Host specificity plays an important role in parasite dispersal, and in the case of avian haemosporidians that are vector-borne parasites, it needs to be evaluated both at the vector and bird host levels. Understanding the effects of these factors on host–vector–parasite dynamics is important to unravel the dispersal and diversification mechanisms of avian haemosporidians. We end this chapter reviewing host specialization in avian haemosporidians of tropical regions, discussing the mechanisms involved in the dispersal and specialization of these parasites and point out important research gaps that need attention