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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Behavioural aspects of bovine tuberculosis (Mycobacterium bovis) transmission and infection in badgers (Meles meles)

Garnett, Benjamin Thomas January 2002 (has links)
No description available.
2

Fitness consequences of cellular immunity : studies with Daphnia magna and its sterilizing bacterial parasite

Auld, Stuart Kenneth John Robert January 2011 (has links)
Immune responses are presumed to contribute to host fitness, either by fighting off infections or via immunopathology. Research in this thesis sought to relate the magnitude of a putative immune response to infection and host and parasite fitness. The experiments and field studies presented here all focus on the interactions between the freshwater crustacean, Daphnia magna and its sterilizing bacterial endoparasite, Pasteuria ramosa, using the number of circulating haemocytes as a measure of host immune activity. I found substantial genetic variation in Daphnia’s cellular response to P. ramosa, and that Daphnia genotypes that mount the strongest cellular responses are the most likely to get infected and suffer sterilization. Thus, a strong cellular response is associated with low, as opposed to high host fitness potential. There were also some host genotypes that mounted a weaker cellular response and did not go on to suffer infection, and some that lacked a cellular response and also never suffered infection with P. ramosa. These findings led to a heuristic two-stage model for infection, where the parasite has to (1) pass from the host gut to haemolymph and then (2) successfully overcome haemolymph-based immune effectors to reproduce and achieve fitness. I also demonstrate that both the magnitude of host cellular response and likelihood of infection increases with initial parasite dose in susceptible host genotypes, and that host cellular response is associated with likely infection under both host and parasite genetic variation. Parasitised Daphnia also have substantially more circulating haemocytes than their healthy counterparts in both the laboratory and in the wild, where there is substantial genetic and environmental variation. This is one of the very few examples of how an immune response designates low host and high parasite fitness potential in a wild system. Finally, using a mixture of field study and common garden experiment, I demonstrate evolution in parasite infection traits over the course of an epidemic in a wild population, and that this evolution is associated with a decline in host abundance.
3

Host-searching behaviour of a generalist egg parasitoid-reponses to alternative hosts with different physical characteristics

Brotodjojo, R. R. R. Unknown Date (has links)
Trichogramma pretiosum Riley is a generalist egg parasitoid that is mass released in biological control programmes to control various insect pests on different plant species. The parasitism rates achieved by T. pretiosum vary across host species and across plant species, which suggests that the species of host and its host plant could both influence the host searching performance of this parasitoid. A comparative behavioural study across the eggs of two moth species, Helicoverpa armigera Hübner and Spodoptera litura Fabricius, was conducted because these two host eggs have different characteristics. Helicoverpa armigera eggs are laid singly, whereas S. litura eggs are laid in clusters and are covered with fine scales from the moth abdomen. I tested how these and other differences in host species affect the behaviour of T. pretiosum females towards their host species. The ovipositional responses of T. pretiosum females, from different natal hosts and of different ages since emergence, to eggs of H. armigera and S. litura were studied in choice and no choice tests. Helicoverpa armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs. The adult lifespan and lifetime fecundity of T. pretiosum were variable but were significantly affected by natal host species and/or host species to which they were exposed. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better, through host feeding, than S. litura eggs. Trichogramma females, like other egg parasitoids, use chemical cues that originate not only from their host plants and host eggs, but also from the adult insects that deposit the hosts. These last include the scales left by the ovipositing moths. These host-associated cues are used by parasitoids over long and short distances to find their hosts. Olfactometer tests demonstrated that the odours from moth scales and host plants attracted T. pretiosum females significantly, and thus function as long range cues. By contrast, the odour from host eggs did not attract them in this way. The strength of attraction was similar across the scales from H. armigera and S. litura moths. The female parasitoids responded most strongly to odours from tomato and cabbage, whereas odour from corn was not such a strong attractant. A non-host plant tested did not attract the parasitoids at all. The odours of moth scales from both H. armigera and S. litura were more attractive to T. pretiosum females than was the odour of the host plants tested. When parasitoids have followed these long range cues to the nearby vicinity of their hosts, they respond to short range cues to localise the hosts. Moth scales did not attract female parasitoids over a short distance, but they did arrest their movement so that they remained longer in the area with scales. Trichogramma pretiosum females took significantly more time to localise S. litura eggs than it took for them to locate H. armigera eggs. Time to locate hosts did not increase significantly when the eggs had been washed with hexane, which suggests that cues other than chemicals are associated with the eggs and play a more significant role in host finding over short distances. On their emergence, parasitoids are confronted by several options, including mating, searching for hosts, and seeking food. Season influenced the daily pattern of T. pretiosum emergence, with cooler winter temperatures extending emergence over two days. In summer they emerged earlier in the day and all parasitoids in the tests emerged during the first day. Parasitoids left their emergence sites by walking before their wings expanded fully. Adults of T. pretiosum visit flowers, presumably for nectar. Olfactometer tests showed that both males and females of T. pretiosum were attracted to the odor of alyssum flowers. The attraction to flower odour was significant for males when they had had no access to nutrients for 24h, but was less significant when they had just emerged. On the contrary, the attraction to food was more significant in newly emerged females. For 1 day starved females, cues associated with host plants (tomato leaves) and food (alyssum flowers) were equally important. Nutritional sources influenced the adult lifespan and reproductive performance of the parasitoids. Honey was the best source of nutrition for adults of T. pretiosum, resulting in the longest lifespan and the highest reproductive output, followed by alyssum flowers, tomato leaves and water. The results are discussed in relation to (i) understanding the entire mechanism of host searching behaviour of egg parasitoids, (ii) interpreting the behavioural interaction between generalist parasitoids and their different host insects and plants, and (iii) the better use of egg parasitoids in biological control. Throughout the discussion suggestions are made for further research.
4

Exploring the Significance of Autophagy in Host Defense in an Enteric Parasitic Infection

Mowna, Sadrina Afrin January 2024 (has links)
Autophagy is a conserved cellular process that is responsible for degrading and recycling cytoplasmic constituents and has also emerged as a significant factor in modulating immune responses during enteric infections. This study investigates the role of autophagy in host defense during enteric parasitic infection, Trichuris muris, by focusing on the host defense, expulsion of worms, infection pathogenesis, and gut microbiota composition. Using C57BL/6 mice that are resistant and AKR mice that are susceptible to T. muris infection, we confirmed that when infected with T. muris, C57BL/6 mice can clear the infection almost completely by day 21 post-infection (p.i.). In contrast, AKR mice cannot, and therefore harbor a chronic infection within. Moreover, autophagy gene 7 floxed mice (Atg7fl/fl) and mice that are deficient in the autophagy protein, autophagy 7, in their intestinal epithelial cells (Atg7ΔIEC), were infected with T. muris and sacrificed on different time points. We observed that the Atg7fl/fl mice were able to almost clear the infection by day 21 p.i. but the Atg7ΔIEC mice were unable to clear infection by day 21 p.i. In vitro experiments consisted of exposing intestinal epithelial (HT-29) cell lines to T. muris excretory secretory products (ESPs) at different concentrations and also for different time-points, however, autophagy protein levels remained unchanged in those concentrations and time-points. Microbiota from uninfected and infected Atg7fl/fl and Atg7ΔIEC, analyzed by 16s rRNA sequencing revealed no significant differences in microbial composition among uninfected mice and minor differences in microbiota composition among T. muris infected mice. / Thesis / Master of Science in Medical Sciences (MSMS)
5

Mimicry and speciation in the parasitic finches of Africa

Jamie, Gabriel Adam January 2017 (has links)
In this thesis, I study a radiation of brood-parasitic finch species, the indigobirds and whydahs (genus Vidua), that occur across Africa. Host colonisation is tightly linked to speciation in Vidua because of their remarkable capacity to imprint on their hosts, with mating traits and host preferences being influenced by the parasite's early environment. The challenge of explaining why the radiation has diversified to the extent it has therefore simplifies to understanding why only certain potential host species have been successfully colonised. Following on from the introduction (Chapter 1), I begin by critically examining the logic with which mimicry in the natural world can be conceptually organized (Chapter 2). This creates a “mimicry landscape” in which to situate the mimetic adaptations of hosts exhibited by Vidua. The framework can be used to contrast and draw parallels between these and other mimetic adaptations present in the natural world. In Chapter 3, I review the literature on begging call mimicry and development across all avian brood parasite species. I outline the conditions under which we expect begging call mimicry to evolve, and when we expect it to develop primarily through genetic or environmental cues. This provides clear predictions for what we expect to occur in Vidua finches, which are tested in Chapters 4 and 5. In Chapter 4, I quantify the mimicry of host nestlings by Vidua in detail. I provide the first quantitative evidence that Vidua nestlings mimic the begging calls and show for the first time that Vidua are imperfect mimics of their hosts. In Chapter 5, I simulate the colonisation of a new host by transferring Vidua eggs into the nest of a new host species. I monitor Vidua survival in the foreign host environment and test several hypotheses about what explains differences in chick survival. I find that Vidua survive poorly in the new nest environment and that they do not show adaptive plasticity in begging calls or head movements. This poor survival occurs despite there being minimal differences in the diets each host species feeds their young. Finally, in Chapter 6, I carry out a comparative analysis on the evolution of estrildid mouth markings. Estrildid finches are the hosts of Vidua and so provide the landscape of potential ecological niches that Vidua may colonise and adapt to. I demonstrate that the host family shows strong phylogenetic signal in mouth marking traits, and find no evidence that ecological factors such as light environment or predation pressure has shaped estrildid mouth marking evolution. The work in this thesis highlights how difficult successfully colonising new hosts is for Vidua finches. Vidua must mimic hosts in multiple traits (mouth markings, begging calls, head movements) to obtain sufficient amounts of food from host parents. Overall, habitat filters, the complex and diverse begging displays of estrildid nestlings, the discriminatory behaviour of estrildid parents against mismatching chicks and the lack of adaptive plasticity in begging displays by Vidua together help explain why the Vidua radiation consists of only 19 species rather than many more or fewer.
6

Erythrocyte invasion by Plasmodium falciparum

Jones, Matthew L. January 2009 (has links) (PDF)
Thesis (Ph.D.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed on Feb. 10, 2010). Includes bibliographical references.
7

Host-parasite relations and sporulation of some smuts of tropical grasses

Fullerton, Robert Alexander. Unknown Date (has links)
No description available.
8

Host-parasite relations and sporulation of some smuts of tropical grasses

Fullerton, Robert Alexander. Unknown Date (has links)
No description available.
9

Community Matters: The Impact of Environmental Factors on Host-Parasite Interactions in Aquatic Systems

Strasburg, Miranda Lynn 15 November 2021 (has links)
No description available.
10

Evolutionary ecology of reproductive strategies in malaria parasites

Carter, Lucy Mary January 2014 (has links)
For vector-borne parasites such as malaria, how within- and between-host processes interact to shape transmission is poorly understood. In the host, malaria parasites replicate asexually but for transmission via mosquitoes to occur, specialized sexual stages (gametocytes) must be produced. Once inside the mosquito vector, gametocytes immediately differentiate into male and female gametes, and motile male gametes must swim through the hostile environment of the bloodmeal to find and fertilise female gametes. Despite the central role that gametocytes play in disease transmission, explanations of why parasites adjust gametocyte production in response to in-host factors remain controversial. Furthermore, surprisingly little is known about the mating behaviour of malaria parasites once inside the mosquito. Developing drugs and/or vaccines that prevent transmission by disrupting sexual stages are major goals of biomedicine, but understanding variation in gametocyte investment and male gamete behaviour is key to the success of any intervention. First, I propose that the evolutionary theory developed to explain variation in reproductive effort in multicellular organisms provides a framework to understand gametocyte investment strategies in malaria parasites. I then demonstrate that parasites appear to change their reproductive strategies in response to environmental cues and in a manner consistent with our predictions. Next, I show how digital holographic microscopy can be used to characterise the morphology and motility of male gametes. I then provide evidence for non-random movement of male gametes and that gamete interactions with red blood cells appear to hinder mating success in a bloodmeal. Finally, I discuss the variation in gametocyte differentiation and fertilisation success when exposed to a number of factors implicated in gametocyte activation. The data presented here provides important information on the basic biology of malaria parasite reproductive stages and demonstrates considerable variation in parasite traits and behaviours in response environmental changes; both in the host and in the mosquito vector.

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