Dissertations / Theses on the topic 'Host-parasite dynamics'
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Rethinavel, Natarajan [UNESP]. "Nonlinear dynamics of within-host parasite competition." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/108886.
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Nesta tese estudamos a biologia de populações de sistemas hospedeiro-parasita, com especial atenção para os efeitos produzidos por múltiplas infecções de diferentes parasitas numa dada população de hospedeiros. Tal situação se assemelha a múlpiplas espécies competindo por um mesmo recurso. Com os parasitas competindo por hospedeiros, diversos resultados no nível populacional podem ocorrer. Se ambos parasitas não puderem infectar um hospedeiro conjuntamente, então o parasita mais apto elimina o menos apto. Quando co-infecções são possíveis, o padrão muda e a coexistência pode ser estabelecida. Finalmente, se um parasita pode deslocar o outro, o assim chamado efeito intraguilda, o resultado dependerá fortemente da taxa de geração de novos hospedeiros, a qual é determinada por fatores ambientais. Nós estudamos este sistema por meio de um modelo matemático su?cientemente abrangente para dar conta destas situações. Procedemos passo-a-passo: começamos com um modelo matemático simples para o caso de um parasita e um hospedeiro. Ao progredirmos para outros casos nosso modelo matemático passa a incluir novos termos até chegarmos num modelo completo. Há dois métodos de análise envolvidos. Estudamos analiticamente a estabilidade do estado livre de infecções, o que nos permite dar condições sobre a capacidade dos parasitas de invadir uma população não infectada/parasitada. Por outro lado, usamos métodos numéricos para estudar o comportamento para grandes tempos, que em todos os casos tende a um ponto ?xo. O foco é saber qual parasita prevelacerá ou se haverá coexistência, além de determinar as condições que regulam o resultado da interação. Através de diagramas de bifurcação analisamos a importância da riqueza de recursos do ambiente, relacionada à taxa de produção de novos hospedeiros. Encontramos que os estados assimptóticos dependem fortemente...
In this thesis we study the population biology of host-parasite systems, with a systematic view of the e?ects produced by multiple infections of di?erent parasites on a same host population. This situation is akin to multiple species competing for a shared resource. As parasites compete for a host, several outcomes at the population level can appear. If both parasites cannot jointly infect the same host, then the ?ttest parasite eliminates the other. When confection is possible, the pattern changes, and coexistence of both parasites becomes possible. Finally, if a parasite can displace the other within the host, the so-called intraguild e?ect, the outcome will strongly be dependent on the income rate of new hosts, which is determined by environmental factors. We studied this system through a mathematical model which is broad enough to encompass these situations. We proceed by steps: ?rst we framed a simple mathematical model for a single parasite/host case and as we progress to other cases, our mathematical model includes new terms and ?nally it is shaped into a complete model. Our methods are twofold. We study analytically the stability of the disease-free state, which allows us to give conditions for the ability of the parasites to invade a disease-free/non-infected population. On the other hand, we resort to numerical methods to study the long-term behavior of the system, which in all cases tends to a ?xed point. The main focus is to know which parasite prevails or if they are able to coexist, and determine the conditions that regulate this outcome . Through bifurcation diagrams we analyzed the importance of the richness of the environment, de?ned by the rate of production of new hosts. We found that the long-term states depend crucially on this rate. Our main original contribution is related to the study of the intraguild e?ect. Depending of the host income rate we can have four di?erent states, which are a disease...
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Rethinavel, Natarajan. "Nonlinear dynamics of within-host parasite competition /." São Paulo, 2013. http://hdl.handle.net/11449/108886.
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Orientador: Roberto André KraenkelBanca: Hilda Cerdeira
Banca: Fernando Fagundes Ferreira
Banca: Mario José de Oliveira
Banca: Stefanella Boatto
Resumo: Nesta tese estudamos a biologia de populações de sistemas hospedeiro-parasita, com especial atenção para os efeitos produzidos por múltiplas infecções de diferentes parasitas numa dada população de hospedeiros. Tal situação se assemelha a múlpiplas espécies competindo por um mesmo recurso. Com os parasitas competindo por hospedeiros, diversos resultados no nível populacional podem ocorrer. Se ambos parasitas não puderem infectar um hospedeiro conjuntamente, então o parasita mais apto elimina o menos apto. Quando co-infecções são possíveis, o padrão muda e a coexistência pode ser estabelecida. Finalmente, se um parasita pode deslocar o outro, o assim chamado efeito intraguilda, o resultado dependerá fortemente da taxa de geração de novos hospedeiros, a qual é determinada por fatores ambientais. Nós estudamos este sistema por meio de um modelo matemático suficientemente abrangente para dar conta destas situações. Procedemos passo-a-passo: começamos com um modelo matemático simples para o caso de um parasita e um hospedeiro. Ao progredirmos para outros casos nosso modelo matemático passa a incluir novos termos até chegarmos num modelo completo. Há dois métodos de análise envolvidos. Estudamos analiticamente a estabilidade do estado livre de infecções, o que nos permite dar condições sobre a capacidade dos parasitas de invadir uma população não infectada/parasitada. Por outro lado, usamos métodos numéricos para estudar o comportamento para grandes tempos, que em todos os casos tende a um ponto fixo. O foco é saber qual parasita prevelacerá ou se haverá coexistência, além de determinar as condições que regulam o resultado da interação. Através de diagramas de bifurcação analisamos a importância da riqueza de recursos do ambiente, relacionada à taxa de produção de novos hospedeiros. Encontramos que os estados assimptóticos dependem fortemente...
Abstract: In this thesis we study the population biology of host-parasite systems, with a systematic view of the effects produced by multiple infections of different parasites on a same host population. This situation is akin to multiple species competing for a shared resource. As parasites compete for a host, several outcomes at the population level can appear. If both parasites cannot jointly infect the same host, then the fittest parasite eliminates the other. When confection is possible, the pattern changes, and coexistence of both parasites becomes possible. Finally, if a parasite can displace the other within the host, the so-called intraguild effect, the outcome will strongly be dependent on the income rate of new hosts, which is determined by environmental factors. We studied this system through a mathematical model which is broad enough to encompass these situations. We proceed by steps: first we framed a simple mathematical model for a single parasite/host case and as we progress to other cases, our mathematical model includes new terms and finally it is shaped into a complete model. Our methods are twofold. We study analytically the stability of the disease-free state, which allows us to give conditions for the ability of the parasites to invade a disease-free/non-infected population. On the other hand, we resort to numerical methods to study the long-term behavior of the system, which in all cases tends to a fixed point. The main focus is to know which parasite prevails or if they are able to coexist, and determine the conditions that regulate this outcome . Through bifurcation diagrams we analyzed the importance of the richness of the environment, defined by the rate of production of new hosts. We found that the long-term states depend crucially on this rate. Our main original contribution is related to the study of the intraguild effect. Depending of the host income rate we can have four different states, which are a disease...
Doutor
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Pascua, Laura del Carmen Lopez. "Environmental and genetic determinants of host-parasite coevolutionary dynamics." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531978.
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Dugaw, Christopher James. "Dynamics of a soil-dwelling parasite and its insect host /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Schaik, Antoon Jacobus van [Verfasser]. "The influence of host social system on host-parasite evolutionary dynamics / Antoon Jacobus van Schaik." Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1118373596/34.
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Gubbins, S. "Dynamics and control of host-parasite systems in heterogeneous and disturbed environments." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599772.
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Using a combination of mathematical analysis, model fitting and parameter estimation, this thesis examines the dynamics and control of host-parasite systems in heterogeneous and disturbed environments. The first chapter introduces and tests models for the population dynamics of Sclerotinia minor, an economically important fungal plant parasite, and the fungal hyperparasite Sporidesmium sclerotivorum in a closed system from which any host of S. minor is excluded. Model structures are identified that reflect experimental data rather than models that are simply mathematical abstractions. Various elaborations of this simple model are discussed in the next chapter and, specifically, the effect of a latent period of infection and the influence of differentiating between primary and secondary infections are considered. In the following chapter, models are developed in which the dynamics of a host crop (lettuce) of S. minor are included. Various mechanisms that contribute to the observed persistence of the parasite are examined and, in particular, the roles played by discontinuities due to planting and harvesting of the lettuce crop, spatial heterogeneity and changes in environmental conditions are considered. Although the models discussed in the first three chapters are developed with close reference to the S. minor-S. sclerotivorum system, they are of broad applicability. In the remaining largely theoretical chapters, the population dynamics of the models are analysed, paying particular attention to thresholds for invasion and persistence. The persistence of host-parasite interactions in disturbed environments (where the host is not continuously present or does not continuously reproduce) is considered first. In the penultimate chapter, thresholds for invasion in plant-parasite systems are derived. These systems are characterised by dual sources of inoculum (primary and secondary infection) and a host response to infection load. Finally, the simple model fitted to the S. minor-S. sclerotivorum data is used to examine the effects of heterogeneous mixing on invasion and persistence.
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Miller, Martin Roy. "Theoretical models for the evolution and ecological dynamics of host-parasite systems." Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/14903/.
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Natural organisms are infected by many different parasites, and as a consequence, hosts have evolved a wide range of defences to cope with them. Resistance may be conferred through mechanisms that reduce susceptibility to infection ('avoidance') or increase the rate of clearance ('recovery'). Other forms of resistance reduce the deleterious effects of infection ('tolerance'), or inhibit the parasite's growth ('control'). In addition to these innate forms, hosts may also benefit from immunological memory ('acquired immunity'). The evolution of resistance is expected to be costly in terms of other life history traits. In the presence of such 'trade-offs', the host population may evolve towards an evolutionarily stable strategy (ESS) that balances the costs and benefits of resistance. Another possibility is that a process of evolutionary branching occurs, leading to polymorphism of distinct strategies. Parasites also show adaptation to their hosts and have generally not evolved to be avirulent. Again, this is the result of trade-offs between virulence and other aspects of life history. Often, a higher transmission rate is attained at the cost of increased virulence. This thesis uses a mathematical modelling approach to examine hostparasite interactions. The first part considers the evolutionary dynamics of quantitative host resistance and parasite traits, employing fitness expressions constructed using the techniques of adaptive dynamics. The second part examines the population dynamics of host-parasite interactions; in particular, how different assumptions about the nature of the transmission process may affect the dynamics.
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Ortega, Nicole. "Flames and Frogs – The Impact of Environmental Disturbances on Host-Parasite Dynamics." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7640.
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The successful completion of this work is dedicated first to my grandparents for having always shown their unwavering love and encouragement in my journeys (most of which they kindly and politely only pretended to understand) and for having also served as life-long role models who upheld an unparalleled work ethic. To many whom I consider to be my chosen family, especially Ann Williams and Brittany Sears, who kept me laughing, but more importantly, kept my crazy train from derailing during these tumultuous years. To Wayne Price and Tom Jackman, who fostered the success of my career and are the epitome of patience and kindness. To DeAngelis, for the many hours of laughter, conversations, and adventuresome treks that further kindled my knowledge, love, and respect for Florida’s ecology. To family in Alabama who have either helped shape my brazen character or made this education possible. To Taego, the one to whom I am bound through so many of the stories that begin with, “Remember when…?” and who is often so kind and thoughtful though he still holds tightly to the stereotype of the selfish youngest sibling. Finally, to Fen for being my smiling, bright blue-eyed, spunky kid who has been on this journey with me from the get-go; for keeping me from getting too big for my britches; for your intrinsic fire that burns for equality, fairness, and friendship; and for inspiring me to be the best example of a mother that I can possibly be.
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Dunlop, Judy. "The ecology and host parasite dynamics of a fauna translocation in Australia." Thesis, Dunlop, Judy (2015) The ecology and host parasite dynamics of a fauna translocation in Australia. PhD thesis, Murdoch University, 2015. https://researchrepository.murdoch.edu.au/id/eprint/29146/.
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Despite the frequency of fauna translocations as a technique to improve the conservation status of threatened species, new populations frequently fail to establish. Translocations often lack experimental manipulation to determine ‘best practice’ methods to improve success. One poorly understood element of translocation science is the impact of parasites and disease-‐causing pathogens on the animals moved and the ecosystem they are moved into. Of 58 published Australian translocations in the last 40 years, only 20 (35%) employed any level of parasite management, despite potential contribution of disease to initial fauna declines.
I closely investigated a translocation of boodies (Bettongia lesueur) from Barrow Island and Dryandra to Lorna Glen, and ‘island dwarf’ golden bandicoots (Isoodon auratus) from Barrow Island to Lorna Glen and Hermite Island. Bandicoots born into the new populations showed an increased skeletal size and body mass (males) and reproductive output in the number and average size of young (females). These changes occurred within 18 months of release, suggesting that responses were due to phenotypic plasticity, rather than selective pressure occurring over many generations. I conclude that the small size of bandicoots on Barrow Island is a response to resource limitation, rather than true island dwarfism.
I determined the impact on parasite load and survivorship of translocated animals by treating half the population with a topical antiparasitic. Despite frequent trapping (six-‐ weekly) and very high recapture rate (64–99%), repeated dosage did not significantly impact ectoparasite or haemoparasite infection, or survival of the marsupials. I observed transmission of parasites between animals of different origin and to offspring, and a decline in species diversity present in the translocated population due to the failure of some species to persist.
This thesis identified knowledge gaps in the translocation literature and addressed some key concepts of species ecology, population dynamics and parasitology via post-translocation monitoring.
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Woodburn, Maureen I. A. "Comparative population dynamics of wild and reared pheasants (Phasianus colchicus)." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323941.
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Betts, Alexander. "The effects of parasite diversity on eco-evolutionary dynamics." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:219e3908-94bb-4fec-897f-cf918cdb37f8.
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Virtually all interacting species (such as hosts and parasites) are embedded within diverse communities. However, evolutionary interactions are typically considered in a pairwise species framework. Although coevolutionary theory suggests that multiple species interactions may provide greater opportunities for diversification, the impacts of community diversity on coevolution have not been directly tested. In this thesis I synthesize the findings from recent experimental work to assess the effects of increased species diversity on the patterns and processes of host and parasite evolution. I then investigate the effects of parasite diversity on host-parasite population dynamics and evolution using the pathogen Pseudomonas aeruginosa and five lytic bacteriophage parasites in a brief evolution experiment. Parasite diversity was manipulated by assembling phage communities with different number of species. Phage communities suppressed host populations more rapidly but also showed reduced phage density, likely due to inter-phage competition. The evolution of resistance allowed rapid bacterial recovery that was greater in magnitude with increases in phage diversity. These results were then followed up via longer term experimental coevolution of the same host and parasite communities. Here the data showed that greater parasite diversity accelerates coevolutionary arms races and drives more diversification among lineages. Coevolution between hosts and parasite communities drove more successive increases in host resistance coupled with increasingly frequent selective sweeps at the genomic level. Consistent with this, the most rapidly evolving host genes under coevolution with parasite communities were those involved in various host resistance strategies. These results demonstrate, at phenotypic and genomic levels, how areas of high community diversity may be hotspots for rapid evolution in interacting, antagonistic species. Finally, In the face of escalating antibiotic resistance, there is now an urgent need to develop alternative antimicrobials, these results may be relevant to the application of phages as therapeutics and they are discussed in that context.
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Bettge, Kathrin. "The proliferative kidney disease of salmonids : dynamics of the parasite in the fish host /." [S.l.] : [s.n.], 2008. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000286556.
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Gordon, David M. "Population dynamics of a host-parasitoid system with particular reference to age-structure effects." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75358.
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An experimental study of laboratory populations of the stored-products moth, Cadra cautella (Lepidoptera: Phycitidae) and its larval parasitoid, Venturia canescens (Hymenoptera: Ichneumonidae) identified and quantified density- and age-dependent demographic characteristics of the host-parasitoid system. Host imago longevity and fecundity depended on larval weight at pupation. Observed effects of C. cautella larval competition for food on larval mortality, stage duration, and weight at pupation were successfully captured in a mathematical model. Host larval age significantly influenced inter-stage cannibalism and susceptibility to mortality resulting from parasitoid oviposition wounds. Both larval parasitoid developmental rates and adult parasitoid attack rates depended on host larval age. Long-term population experiments of host and host-parasitoid populations revealed that host populations fluctuated with a period slightly in excess of host generation time and that parasitoid populations were in synchrony with host populations.
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González, Tortuero Enrique [Verfasser], and Justyna [Akademischer Betreuer] Wolinska. "Host-parasite dynamics in a natural system : revealing the evolutionary change in parasite populations infecting Daphnia / Enrique Gonzalez Tortuero ; Betreuer: Justyna Wolinska." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1119073332/34.
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Ferrari, Nicola. "Macroparasite transmission and dynamics in Apodemus flavicollis." Thesis, University of Stirling, 2005. http://hdl.handle.net/1893/105.
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This thesis examines the parasite dynamics and the mechanisms affecting parasite load and transmission focalising on the role played by host and habitat heterogeneities. This study is based on the gastrointestinal nematode Heligmosomoides polygyrus and the small mammal yellow necked mouse and uses data gathered from experimental field manipulations of parasites intensities and data gathered from trapping monitoring. Initially the parasite community of yellow-necked mouse (Apodemus flavicollis) was explored in North-Eastern Italian Alps with the aim to describe the major patterns and identify the factors affecting parasite community structure. Despite the observed spatial variability it has been found that differences within the host population such age and secondly sex and breeding conditions, were the major factors acting on parasite occurrence and intensity. Habitat differences had a less apparent effect on parasite community structure. The consequences of H. polygyrus infection on other parasite species infections have been analysed, in specific the infestation of the tick Ixodes ricinus in populations of A. flavicollis. H. polygyrus load and tick infestation were monitored as well as were carried out field manipulations of H. polygyrus intensity and were monitored changes in tick infestation. It has been found that H. polygyrus load was negatively related to I. ricinus infestations. Host factors mediated the H. polygyrus-I. ricinus interaction such that young and non-breeding mice exhibited higher I. ricinus to H. polygyrus intensity respect breeding adults. The role of host sex on parasite abundance was then investigated carrying out a field experiment where the H. polygyrus intensity were manipulated in relation to mice gender. In specific, H. polygyrus was removed alternately from either sexes and the parasite load was analysed in the untreated sex. It was found that males mice were responsible to drive parasite transmission in the host population and this was observed in absence of sex-bias in parasite infection, suggesting that this pattern was not a mere consequence of quantitative differences in parasite loads between sexes. To disentangle the possible mechanism causing this sex bias in parasite transmission mathematical simulations based on parameters obtained for the field experiment were used. Two non mutually exclusive hypotheses causing sex bias in parasite transmission were tested: a- males immune response is less efficient and this causes the development of more successful parasite infective stages or b-males behaviours allow them to be more efficient is spreading in more exposed areas parasite infective stages. Multi-host models were developed and simulations were compared with field results. While it was not disentangled the most dominant mechanism causing sex bias in parasite transmission this study underlined the importance of host sexes in affecting parasite dynamics and host-parasite interaction. In conclusion this thesis highlighted the importance of considering host and environmental differences when investigating host parasite interactions. This finding could be extremely important when planning measured of disease control or to avoid disease outbreak. Controlling target group of individuals host could avoid economical losses and a more effective measure of intervention.
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Bauer, Sabine. "Coevolutionary dynamics and geographic mosaics in the Social Parasite Harpagoxenus sublaevis and its two Host Species." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-107521.
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Rosà, Roberto. "The importance of aggregation in the dynamics of host-parasite interaction in wildlife : a mathematical approach." Thesis, University of Stirling, 2003. http://hdl.handle.net/1893/50.
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This study examines, from a modelling point of view, the dynamics of infectious diseases in wildlife caused by macroparasites and by tick-borne infections. The overall aim was to investigate the important role played by parasite aggregation in the dynamics of both systems. For macroparasites we first developed some deterministic models that incorporate explicit mechanisms for generating aggregation in parasite distribution, specifically multiple infections and host heterogeneity. We explored the role of aggregation in host regulation and in determining a threshold value for parasite establishment. A large aggregation makes it more difficult for parasites both to regulate hosts, and to get established in a population at carrying capacity. Furthermore, the stabilization yielded by aggregation strongly depends on the mechanism that produces the aggregation. We then introduced some uncertainties into the host-macroparasite system, presenting an individual-based stochastic model that incorporated the same assumptions as the deterministic model. Stochastic simulations, using parameter values based on some real case studies, preserved many features of the deterministic model, like the average value of the variables and the approximate length of the cycles. An important difference is that, even when deterministic models yield damped oscillations, stochastic simulations yield apparently sustained oscillations. The amplitude of such oscillations may be so large as to threaten the parasites’ persistence. With respect to tick-borne diseases we presented a general model framework that incorporated both viraemic and non-viraemic routes of infections. We compute the threshold for disease persistence and study its dependence on the parameters and on host densities. The effects of tick aggregation and correlation between different tick stages on the host have both an important effect on infection persistence, if non-viraemic transmission occurred. In the case of Lyme Disease and Tick-borne Encephalitis (TBE) in Trentino (northern Italy) we showed some numerical results, using parameter estimates based on a detailed field study, and explored the effects of uncertainty on the endemic equilibrium of both diseases assuming only viraemic transmission for Lyme Disease while for TBE we permitted only non-viraemic transmission through co-feeding ticks. In conclusion we have examined the patterns and changes of aggregation in a number of contrasting systems and believe that these studies highlight both the importance of considering heterogeneities in modelling host-parasite interactions and, more specifically, modelling the biological mechanisms that produce aggregation in parasite distributions.
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Isomursu, M. (Marja). "Host–parasite interactions of boreal forest grouse and their intestinal helminth parasites." Doctoral thesis, Oulun yliopisto, 2014. http://urn.fi/urn:isbn:9789526203645.
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Abstract Parasites are an inseparable part of the life of wild birds. They may cause morbidity, mortality or reduction in fecundity. Parasite distribution in hosts is typically not uniform and many host factors (e.g. age) may affect the pattern of distribution. Under certain conditions, parasites even have the potential to regulate the host population. The grouse species of Finnish forests — the capercaillie Tetrao urogallus , the black grouse Lyrurus tetrix and the hazel grouse Tetrastes bonasia — harbour several species of intestinal helminth parasites. The populations have fluctuated in cyclic manner but the mechanisms behind the cycles are largely unknown. I studied the interactions of forest grouse and their intestinal helminth parasites by using intestinal samples collected by hunters in five game management districts during eight years (1995–2002). The most common parasite species in the samples was the nematode Ascaridia compar. Also, three species of cestodes (Skrjabinia cesticillus, Paroniella urogalli and Hymenolepis sp.) were found. Large size, male gender and age over 1 year were connected with an increased probability and intensity of A. compar infection. Juvenile grouse were commonly infected with cestodes while in adults infections were quite rare. The influence of inbreeding on the susceptibility to parasite infections was studied in the capercaillie by analysing microsatellite heterozygosity. The less heterozygous birds were more likely to be infected with A. compar and were more intensely infected suggesting negative influence of inbreeding on parasite resistance. An indirect negative effect of parasites was found by comparing bags hunted with a trained dog or without a dog. Grouse infected by cestodes were significantly more common in the dog-assisted bag. Thus, cestode infection seemed to make grouse more vulnerable to canine predation. The interaction between grouse population dynamics and parasites was studied by analyzing the grouse densities obtained from annual wildlife counts and parasite indices. A. compar was most common and most abundant in the years of grouse population decline. The grouse population growth rate was negatively correlated with the annual mean abundance of A. compar. Relative survival but not breeding success decreased as the abundance of A. compar increased. The findings suggest that A. compar influences the dynamics of Finnish grouse even though regular cyclic dynamics are no longer evidentTiivistelmä Loiset kuuluvat erottamattomana osana luonnonvaraisten lintujen elämään. Ne voivat aiheuttaa sairautta, kuolleisuutta tai hedelmällisyyden alentumista. Tyypillisesti loiset ovat levinneet isäntäpopulaatioon epätasaisesti ja monet isännän ominaisuudet (esim. ikä) vaikuttavat levinneisyyteen. Tietyissä oloissa loiset voivat jopa säädellä isäntäpopulaatiotaan. Suomalaiset metsäkanalinnut — metso Tetrao urogallus, teeri Lyrurus tetrix ja pyy Tetrastes bonasia — ovat useiden suolistoloismatolajien isäntiä. Metsäkanapopulaatiot ovat vaihdelleet syklisesti, mutta syklejä aiheuttavat mekanismit ovat yhä tuntemattomia. Tutkin metsäkanalintujen ja niiden suolistoloisten välisiä vuorovaikutuksia käyttäen metsästäjien vuosina 1995–2002 viidestä eri riistanhoitopiiristä keräämiä suolistonäytteitä. Yleisin loislaji näytteissä oli kanalintusuolinkainen, Ascaridia compar. Myös kolme heisimatolajia (Skrjabinia cesticillus, Paroniella urogalli ja Hymenolepis sp.) todettiin. Suuri koko, koirassukupuoli ja yli yhden vuoden ikä olivat yhteydessä suurempaan kanalintusuolinkaistartunnan todennäköisyyteen ja voimakkuuteen. Nuorilla (alle 1 v.) linnuilla heisimadot olivat yleisiä, kun taas aikuisilla tartunnat olivat varsin harvinaisia. Sisäsiittoisuuden vaikutusta loistartuntaherkkyyteen tutkittiin metsolla mikrosatelliittiheterotsygotian perusteella. Vähemmän heterotsygoottiset metsot olivat todennäköisemmin ja voimakkaammin suolinkaisten infektoimia, mikä viittaa sisäsiittoisuuden negatiiviseen vaikutukseen loisten vastustuskykyyn. Loisten epäsuora haitallinen vaikutus havaittiin, kun verrattiin koiran kanssa ja ilman koiraa metsästettyä lintusaalista. Heisimadot olivat selvästi yleisempiä linnuilla, jotka oli metsästetty koiran kanssa kuin ilman koiraa metsästetyillä. Heisimatotartunta näytti siis altistavan metsäkanoja koiraeläinten saalistukselle. Metsäkanalintu- ja loispopulaatioiden välistä vuorovaikutusta tutkittiin analysoimalla vuosittaisia metsäkanatiheyksiä ja loisten runsautta. Kanalintusuolinkainen oli yleisimmillään ja runsaimmillaan metsäkanatiheyden laskuvuosina. Metsäkanapopulaation vuosittainen kasvuvauhti korreloi negatiivisesti kanalintusuolinkaisen vuosittaisen runsauden kanssa. Suhteellinen elossasäilyvyys laski kanalintusuolinkaisen runsauden lisääntyessä, mutta lisääntymistuloksen suhteen ei ollut samaa ilmiötä. Löydökset viittaavat siihen, että kanalintusuolinkaisella on vaikutusta suomalaisten metsäkanalintukantojen vaihteluihin, vaikka syklisiä kannanvaihteluja ei enää havaitakaan
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Davies, Claire Louise. "Parasite dynamics and community richness in a naturally fragmented water vole (Arvicola amphibious) metapopulation." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228192.
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Fragmentation can drive local populations to become smaller and more isolated, and consequently more susceptible to extinction. Movement between patches, however, can interconnect such populations so that they effectively behave as larger and more stable metapopulations. Over the past two decades metapopulations have been used to shed light on the complex interactions that occur between hosts and parasites. Effectively every host can be considered as a discrete habitat patch from the perspective of a parasite. As such, host-parasite interactions naturally lend themselves to being examined within the metapopulation paradigm. In this thesis I examine empirically how various aspects of metapopulation structure, such as local host population size and landscape isolation/connectivity, combine to determine the extinction and recolonization dynamics of parasites in the landscape. Using a naturally fragmented water vole (Arvicola amphibious) metapopulation, I describe the spatial and temporal variation in parasite infection prevalence or burden in a Scottish landscape. I specifically address the spatial and temporal dynamics of both ectoparasites, and vectortransmitted microparasites, since these are two groups of parasites commonly found in natural systems yet often overlooked in the host-parasite metapopulation literature. In addition, I attempt to understand how specific parasite characteristics, such as transmission mode and infectious period, can influence how parasites respond to host population structure. In the final chapter, I bring together a number of parasite groups to examine the impact of metapopulation dynamics on parasite communities as a whole by investigating its impact of parasite community richness. Overall the findings of my study indicate that host spatial structure and the level of connectivity between patches are important factors that affect parasite dynamics and community richness. However, the exact level of connectivity required to sustain a parasite population locally depended on specific parasite characteristics. In contrast, local effects host/vector population size and patch infection history) had no discernible impact on most parasite groups.
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Earnhart, Christopher G. "Dynamics of the host-parasite interaction: in vitro correlates of Crassostrea-induced modulation of Perkinsus marinus function." W&M ScholarWorks, 2004. https://scholarworks.wm.edu/etd/1539616637.
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Perkinsus marinus is an alveolate protozoan parasite of the eastern oyster (Crassostrea virginica) which is responsible for much of the decline in United States oyster populations. Perkinsus marinus can be cultured in vitro, but is rapidly attenuated in the process. Supplementation of a protein-free medium with oyster products altered proliferation, changed protease expression in the parasite extracellular products (ECP), induced morphological forms typically seen in vivo, and partially reversed parasite attenuation. Supplements derived from dissected oyster tissues were used to determine if these changes could be differentially elicited. These supplements, with the exception of adductor muscle, reduced proliferation. Whole oyster and digestive gland/gonad supplements favored palintomic, rather than binary, fission. The total ECP protease activity was generally decreased in supplemented cultures, though gill/mantle supplements may have induced proteases. A low molecular weight subset of proteases was upregulated most effectively by heart- and adductor muscle-derived supplements. Serine proteases and other ECP proteins may be virulence factors. Attempts to create antibodies to study P. marinus cells and ECP have been largely unsuccessful due to poor immune responses and crossreactivity. Ultrafiltration-concentrated P. marinus ECP were poorly immunogenic and toxic to experimental animals. Immunogenicity was not substantially affected by heat denaturation or proteolytic inhibition. Co-administration of ECP with oyster plasma caused a suppression in the anti-plasma antibody response with restriction of epitope recognition. Analysis of medium constituents revealed that a surfactant, Pluronic F-68 (PF68), was immunosuppressive. Although isolated protein antigens from the ECP remained immunosuppressive, separation of the antigens from PF68 enabled antibody production. Five monoclonal antibodies were created against ECP from unsupplemented medium and were used to study ECP function, regulation, and mechanism of storage and release. ECP are secreted by release from the cell wall and from two morphologically distinct intracellular compartments. A sandwich ELISA allowed quantification of an ECP protein with significantly reduced expression in supplemented cultures. Another antibody, which specifically bound to trophozoite and tomont walls, was used to investigate morphological and antigenic changes during thioglycollate-induced formation of prezoosporangia, and confirm supplement-induced formation of prezoosporangia. This antibody labeled P. marinus cells in fixed oyster tissue in a species-specific manner.
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Archer, Elizabeth. "The effects of rainfall and sociality on host-parasite dynamics in the common mole-rat, Cryptomys hottentotus hottentotus (Lesson 1812)." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/79253.
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There are many factors which may influence the distribution of parasites and often parasites are not evenly distributed amongst their hosts. The development and survival of ectoparasites is usually dependent on abiotic factors such as temperature and rainfall. Therefore differences in ectoparasite load between host populations and seasonal fluctuations in abundance are often found to be associated with climatic variations. However, biotic (host-related) factors have also been found to play a role in these differential infection rates. Host social aggregations during the breeding season have been shown to enhance horizontal transfer of ectoparasites due to increased host density. As a consequence, the question arises as to whether an increase in parasitism comes as a cost to social species. Recently, a number of studies have started to assess whether particular individuals within social groups tend to suffer higher parasitic burdens as a consequence of their social status. Some of these studies have employed the analysis of testosterone and glucocorticoid concentrations in the host in relation to these factors. Both of these steroid hormones may have immunosuppressive effects when their circulating concentrations increase. Additionally, each can vary with the seasons and the social environment. To date universal trends have not been reported for either abiotic or biotic factors in association with parasite load. Therefore, this study aimed to provide a comprehensive report of the ectoparasitic fauna associated with the social, subterranean rodent Cryptomys hottentotus hottentotus. Differences in parasite prevalence and abundance were analysed across two habitats at the extremes of a rainfall gradient within which the host species is found. Once the inventory had been compiled, the impact of abiotic and biotic factors was assessed across the two populations to determine which was the most influential on parasite dynamics. The study also attempted to assess whether parasitism was costly to sociality and if certain members of the colony suffered greater parasitism due to their social status. Testosterone and glucocorticoid concentrations were also measured and compared against factors such as season, breeding status and parasitic infection. The ectoparasite communities were very similar between populations, inferring that the subterranean environment has led to specialisation of ectoparasites on C. h. hottentotus. The confinement of being underground also appears to have made the ectoparasite community more dependent on the host. Seasonal increases in parasite prevalence and abundance are thought to be linked to increased host dispersal and social interactions that occur during peak rainfall. However, there were distinct differences in parasite load between locations. Additionally, few common patterns were found between separate parasite taxa. Group size either did not influence or reduced mite abundance, suggesting sociality is beneficial to the host. However, differences between hosts of different social status were more difficult to assess, particularly as this may differ between locations. It is unlikely that any differences in parasite burden observed between individuals are a direct result of immunosuppression from steroid hormones. In conclusion there are many factors which may influence the host-parasite relationship simultaneously and therefore generate unique circumstances within each host population.Dissertation (MSc)--University of Pretoria, 2013.
Zoology and Entomology
MSc
Unrestricted
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Clarke, Charlotte Louise. "Investigating the host-parasite dynamics of a novel amphibian dermocystid disease in an isolated population of palmate newts in the UK." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28815.
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Emerging infectious diseases (EIDs) have been identified as a key factor in significant amphibian mortalities and global declines. Disease has been largely attributed to just two pathogens, Batrachochytrium dendrobatidis (Chytrid) and Ranavirus, however, an increasing number of amphibian disease cases across Europe are being attributed to a group of unusual fungal-like pathogens of the order Dermocystida. Despite representing an old lineage of amphibian pathogens first described in 1903, very little is known about amphibian- Dermocystids. In 2006, diseased palmate newts on the Isle of Rum, Scotland were reported. Clinical signs appeared consistent with heavy infestations of Dermocystid disease, however oedematous pathologies not previously described in the literature were also observed, suggesting a severe case of disease. This thesis develops the first comprehensive pathogen profile of a novel amphibian-infecting Dermocystid causing severe disease in an isolated population of palmate newts (Lissotriton helveticus) on the Isle of Rum, Scotland. Molecular phylogenetics and histopathology techniques were used to characterise the pathogen, confirming its affiliation to the Dermocystids and identifying it as the second formally described species in the genus Amphibiothecum (meredithae). By incorporating histopathology, field observations and study trials a broader understanding of disease dynamics was achieved. Pathogen cyst developmental stages were assigned to distinct gross pathologies, determining a putative disease cycle. In addition, a large disparity in disease outcome was evident, with cases suggesting involvement of innate immune systems with apparent host recovery, alongside cases with severe morbidity and mortality. Following the development of a pathogen profile, the spatio-temporal dynamics of disease were explored across three consecutive years, from 2014 to 2016. The temporal patterns observed within a single season were first examined across a small sub-set of sites, highlighting a degree of stability in disease prevalence and environmental variables. This within-season survey also provided a temporal dataset of disease presentation, allowing for disease progression to be assessed at the population level, investigating the impact of time on disease presentation and morbidity. For example, an overall linear trend in disease progression was observed where the burden of discrete cysts, thought to represent an initial stage of infection was highest at the beginning of the season, appearing to be ‘replaced’ by larger lesions representing later stage pathologies. Finally, ulcerations that facilitate the release of mature pathogen spores (or sporangia) occurred in the highest abundance towards the end of the season. However the prevalence of the most severe oedematous stages did not always fit with this linear progression of disease and may be driven by other factors. Understanding the within-season dynamics, and confirming a temporal stability in disease prevalence, allowed for broader spatial analysis to be performed without the need to account for samples taken at different points in time. Data collected from a broad spatial survey conducted in 2014 was explored to determine the spatial distribution of infection on Rum, and to investigate the relationships between the incidence, prevalence and severity of disease to environmental conditions and host population structure (e.g. sex ratios). Disease was widespread but heterogeneously distributed across Rum, with site-to-site variation in the incidence and prevalence linked to water pH where low pH environments were associated with low disease prevalence. An apparent sex-linked bias in disease was determined where males were more susceptible, but this does not appear to impact the host population structure of infected sites. The observed relationships between disease prevalence and environmental conditions were further utilised to test the use of disease prediction maps as a means to estimate disease across unsampled locations on the Island. Spatial surveys were subsequently conducted in 2015 and 2016, providing annual data on the distribution and prevalence of disease. Interannual variation at the site level was used to explore key factors influencing the stability of disease, identifying an association between changes in host population structure and increasing disease levels. Spatio-temporal fluctuations at the island level alluded to the overall state of disease on the island and changes to disease risk overtime. Whilst spatial clusters of changing disease prevalence were identified, which could indicate unusual patterns of epidemic spread, these conclusions would be speculative and as no consistent, significant increase in disease was determined or expansion in range, disease likely represents an endemic infection dictated heavily by etiological factors. In order to facilitate future studies and nation-wide surveys such as those conducted for Chytridiomycosis and Ranavirosis, this thesis concludes by trialling non-invasive diagnostic techniques. Environmental DNA and dermal swabbing provides the basis for the development of alternative sampling protocols to improve large-scale survey potential, and lead to a deeper understanding of these pathogens. This study represents the first formally described case of Dermocystid in the UK as well as providing the first detailed spatio-temporal study of an amphibian- Dermocystid. Identifying significant predictors of disease alongside disease prediction maps and potential methods for quick disease diagnosis, provides the tools for future, large-scale analyses to understand the distribution of disease across mainland UK, host range and the risk to native amphibian species.
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Wille, Michelle. "Viruses on the wing: evolution and dynamics of influenza A virus in the Mallard reservoir." Doctoral thesis, Linnéuniversitetet, Institutionen för biologi och miljö (BOM), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-41431.
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This thesis explores the evolution of avian influenza A viruses (IAV), as well as host-pathogen interactions between these viruses and their main reservoir host, the Mallard (Anas platyrhynchos). IAV is a genetically diverse, multi-host virus and wild birds, particularly dabbling ducks, are the natural reservoir. At our study site, up to 30% of migratory Mallards are infected with IAV during an autumn season, and host a large number of virus subtypes. IAV diversity is driven by two main mechanisms: mutation, driving genetic drift; and reassortment following co-infection, resulting in genetic shift. Reassortment is pervasive within an autumn season, both across multiple subtypes and within a single subtype. It is a key genetic feature in long-term maintenance of common subtypes, as it allows for independent lineage turn-over, generating novel genetic constellations. I hypothesize that the decoupling of successful constellations and generation of novel annual constellations enables viruses to escape herd immunity; these genetic changes must confer antigenic change for the process to be favourable. Indeed, in an experiment utilizing vaccines, circulating viruses escaped homosubtypic immunity, resulting in the proliferation of infections with the same subtype as the vaccine. While the host plays an important role in shaping IAV evolutionary genetics, one must consider that Mallards are infected with a multitude of other microorganisms. Here, Mallards were infected with IAV, gamma coronaviruses, and avian paramyxovirus type 1 simultaneously, and we found a putative synergistic interaction between IAV and gamma coronaviruses. Mallards occupy the interface between humans, poultry, and wild birds, and are the reservoir of IAV diversity. New incursions of highly pathogenic H5 viruses to both Europe and North America reaffirms the role of wild birds, particularly waterfowl, in diffusion of viruses spatially. Using European low pathogenic viruses and Mallard model, this thesis contributes to aspects of epidemiology, ecology, and evolutionary dynamics of waterfowl viruses, particularly IAV
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Multeau, Cecilia. "Contribution à l'étude du potentiel d’utilisation des Densovirus en lutte microbiologique." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20081/document.
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La lutte microbiologique connaît un regain d'intérêt suite aux problématiques soulevée spar les pesticides chimiques en agriculture. L'objectif de ces travaux de thèse est d'étudier le potentiel d'une ressource virale alternative, les Densovirus pathogènes de Lépidoptères,appartenant à la sous famille des Densovirinae, strictement inféodée aux Arthropodes. Nos travaux ont été axés sur trois points (i) décrire le spectre d'hôtes de deux Densovirus candidats et identifier des déterminants de spécificité pour comprendre l'évolution du spectre d'hôtes ; (ii) caractériser des mécanismes de transmission horizontale pour analyser la dynamique de l'infection et (iii) valider des outils de détection des Densovirinae afin d'étudier la diversité génétique virale dans la nature. Le premier axe nous a permis d'identifier (i) un Densovirus candidat qui ne semble être virulent que pour des Lépidoptères ravageurs de culture, et (ii) des déterminants de spécificité à la surface de la capside impliqués le franchissement de la barrière intestinale. Concernant la transmission, nos résultats montrent qu'un Densovirus se propage rapidement dans une population hôte en induisant un comportement cannibale probablement développé par les individus non infectés. Nous avons également caractérisé deux mécanismes de transmission horizontale,par morsures et par un vecteur endoparasitoïde. Enfin, pour étudier la prévalence virale,nous avons mis au point un protocole basé sur le principe d'une PCR nichée que nous avons testé sur des insectes collectés dans la nature. Ceci nous a permis de dresser un inventaire de la diversité d'insectes, sans toutefois révéler à ce jour la présence de Densovirinae. Ces résultats constituent les premières connaissances pour l'élaboration d'un modèle épidémiologique qui nous permettra d'évaluer l'impact sur l'environnement d'utiliser un Densovirus en tant qu'agent de lutte microbiologiqueMicrobial control has a renewed interest due to issues raised by chemical pesticides inagriculture. The aim of this work is to propose a new viral resource, Densoviruses pathogenicfor Lepidoptera belonging to Densovirinae sub‐family restricted to arthropods. We focus onthree axes, (i) we described the host range of two Densovirus candidates, and identified hostspecificity determinants to understand host range evolution; (ii) we characterized themechanisms driving the horizontal transmission of Densovirus to model the dynamic of theinfection; and (iii) we validated tools to detect Densovirinae to study the viral geneticdiversity in natura. The first point lead us to identify (i) a Densovirus potentially pathogeniconly for lepidopteran pests, and (ii) few determinants of specificity localized at the surface ofthe capsid that are essential for the midgut recognition, although this barrier of specificity isnot the only one. Concerning horizontal transmission, our results show that a Densovirus canspread rapidly within a host population, inducing a cannibalistic behavior probablydeveloped by non infected individuals. We also characterize two mechanisms involved intransmission, by biting and by an endoparasitoïd vector. To study the densoviral prevalence,we develop a nested PCR and test it on insect sampling. This allowed us to describe theinsect diversity. No Densovirinae have been detected so far. These results are the first steptoward building an epidemiology model that may allow to evaluate the impact of using aDensovirus as a biological control tool
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Tsao, Jean Ijieh. "Vertebrate host community composition and the dynamics of borrelia burgdorferi, the etiologic agent of lyme disease : theory and experiments /." 2000. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9990602.
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Curson, David R. "Host community dynamics and reproductive biology of a generalist avian brood parasite, the brown-headed cowbird /." 2003. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Bauer, Sabine [Verfasser]. "Coevolutionary dynamics and geographic mosaics in the social parasite Harpagoxenus sublaevis and its two host species / vorgelegt von Sabine Maria Veronika Bauer (geb. Demel)." 2009. http://d-nb.info/998370851/34.
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Reichardt, Todd Raymond. "The seasonal dynamics and host-parasite relationship of Opisocrostic bruneri (Baker), a flea on Franklin's ground squirrel, Spermophilus franklinii (Sabine) near Birds Hill Park, Manitoba." 1989. http://hdl.handle.net/1993/7181.
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The host-parasite relationship between the flea, Opisocrostis bruneri and its primary host, Franklin's ground squirrel, Spermophilus franklinii was evaluated during a 2 year study. Adult male ground squirrels were first captured each year on 5 May. The adult males were reproductively fit during the first two weeks of May. Adult female squirrels were first captured 5-8 days after the first male capture. Mating and subsequent parturition probably occurred in early May and mid-late June, respectively. The first observed signs of above ground juvenile squirrel activity were in mid-July. Adult squirrels immerged to hibernate in early August, followed by the juvenile females and males in early to mid-September. Thirty-six individual squirrels were involved in 95 total captures in 1982. In 1983, 40 individual squirrels were involved in 161 total captures. The recapture rate of S. franklinii was 2.6 and 4.0 in 1982 and 1983, respectively. Adult squirrels constituted approximately 75% of the total captures and this stage was most frequently recaptured in 1982 and 1983. Eight hundred and forty-nine and 1503 O. bruneri were removed from S. franklinii in 1982 and 1983, respectively. Adult male squirrels were most frequently infested and contributed 43% and 64% of fleas collected in 1982 and 1983, respectively. The observed sex ratio (m/f) of fleas removed from S. franklinii was 0.70 and 0.73 in 1982 and 1983, respectively. The biweekly sex ratio (m/f) favoured female fleas in each trapping period throughout the season except during a two week period starting at the beginning of May and the end of June. The observed prevalence of O. bruneri from all captured S. franklinii was greater than or equal to 0.75. The observed biweekly prevalence on adult male and female squirrel was always greater than or equal to 0.73 and 0.67, respectively. Juvenile male and female squirrels were always infested. Two discrete peaks of mean intensity of adult fleas were observed in early May and late August. Female fleas containing immature ovarioles (stage 0 and 1) with or without sperm in the spermatheca were predominant during the first three trapping periods. Parous females predominated during the remaining trapping periods. Oogenesis of O. bruneri was not stimulated by the oestrous cycle of female S. franklinii. Parous female fleas containing sperm within the spermatheca were found throughout the entire season...
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Ho, Yei-Long, and 何宜龍. "Dynamical aspects of host-parasite associations." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/96880602601450079757.
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