Includes bibliography.

We are interested in modeling some two-level population dynamics, resulting from the interplay of ecological interactions and phenotypic variation of individuals (or hosts) and the evolution of cells (or parasites) of two types living in these individuals. The ecological parameters of the individual dynamics depend on the number of cells of each type contained by the individual and the cell dynamics depends on the trait of the invaded individual. Our models are rooted in the microscopic description of a random (discrete) population of individuals characterized by one or several adaptive traits and cells characterized by their type. The population is modeled as a stochastic point process whose generator captures the probabilistic dynamics over continuous time of birth, mutation and death for individuals and birth and death for cells. The interaction between individuals (resp. between cells) is described by a competition between individual traits (resp. between cell types). We look for tractable large population approximations. By combining various scalings on population size, birth and death rates and mutation step, the single microscopic model is shown to lead to contrasting nonlinear macroscopic limits of different nature: deterministic approximations, in the form of ordinary, integro- or partial differential equations, or probabilistic ones, like stochastic partial differential equations or superprocesses. The study of the long time behavior of these processes seems very hard and we only develop some simple cases enlightening the difficulties involved.

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Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 117-134).

Social parasitism, the exploitation of a society by other social organisms, has evolved independently numerous times within social animals. In this thesis, I integrate behavioral, evolutionary and chemical analyses to elucidate the evolution of social parasitism in Megalomyrmex ants. I examine host-parasite interactions in two Megalomyrmex species, identify venom alkaloids, and reconstruct the phylogenetic relationships between species. In Chapter 1, I analyze nest architecture and behavioral interactions between the ant host Cyphomyrmex cornutus and its parasite Megalomyrmex mondabora. This is the first detailed account of the natural history of this host and its social parasite. In Chapter 2, I report a one-year-long fitness experiment that tests whether Trachymyrmex cf. zeteki colonies suffer reduced fitness from an association with the social parasite Megalomyrmex symmetochus. I show that M. symmetochus parasites negatively impact host fitness though several mechanisms, including a) manipulation of the host worker grooming behavior; b) castration of host queens produced by the host colony, which then become workers; and c) reduction of garden size, host worker number, and host reproductive output. In Chapter 3, I determine that five venom alkaloids of Megalomyrmex are taxonomically informative to help differentiate cryptic species within the M. mondabora complex; new species in this complex need to be described in a future taxonomic revision. In Chapter 4, I reconstruct phylogenetic relationships of the genus Megalomyrmex with DNA sequence information. I conclude that the genus is monophyletic and corroborate two of the four species groups proposed by Brandão (1990) in a previous morphological revision. I also find evidence in support of Darwin’s Predation Hypothesis on the origin of social parasitism, which postulates that socialparasitic behaviors evolve from predatory behaviors. Lastly, I discuss promising future research directions on the evolution of social parasitism in the ant genus Megalomyrmex, which could serve as a model for the study of social parasitism in other lineages of social insects. / text

Lernaea spp. was identified as a widespread problem in West Malaysia and various aspects of the parasite were studied. A survey of the distribution of Lernaea spp. in West Malaysia revealed its presence in all the 8 government owned fish breeding stations, 104 privately owned farms and 4 out of 5 consignments of imported fingerlings. The Lernaea spp. present in these ponds were identified as L. piscinae and L. cyprinacea "Asian" form (=b.elegans) and its morpha forms, L. ctenopharyngodonis and L.guadrinucifera. The life cycles of L. cyprinacea and L. piscinae were determined under laboratory conditions. Infection of ~. auratus with the offspring of L. cyprinacea "Asian" form produced adult females similar to the maternal form and another form identified as b. ctenopharyngodonis. A. nobilis, infected with L. cyprinacea "Asian" form and L. piscinae produced only species identical to the maternal form. A high degree of polymorphism was revealed and was further investigated. Morphometric studies on the larval stages and adult female parasites were investigated and reliable characteristics for the identification of Lernaea is discussed. The distribution frequency of b. cyprinacea on 3 host species and L. piscinae on A. nobilis in aquarium tanks was goodness of tested for/fit with the theoretical negative binomial distribution. The bases of fins were found to be the preferred site of infection for both species. studies on growth performance of A. nobilis infected with L. piscinae in ponds, revealed a significant reduction in Specific Growth Rates. Infected fish had a higher mortality than uninfected fish. A decrease in parasite infection on the body surface after 3 months was associated with its appearance in the eye. A challenge infection did not establish and the fish were suspected of being immune. Histopathological studies showed a typical inflammatory response with the formation of a granuloma. Eosinophilic granular cells, lymphocytes, and club cells which were identified in the hosts immune to the infection, were believed to play an important role in the rejection of parasites.

No description available.

No description available.

Natural selection should favour host defenses that reduce a host’s exposure to parasites or reduce their negative effects. One strategy that resolves the substantial costs of host immunity and/or tolerance is to avoid infective stages altogether. For fish, behavioural avoidance is well-known for defense against aquatic predators, but it is poorly known for defense against parasites. I used a model system that is amenable to experimental manipulation to test the behavioural avoidance hypothesis for fathead minnows exposed to the larvae of two of their common flatworm parasites. First, I showed that minnows exposed to a liver encysting trematode, Ornithodiplostomum sp. showed an increase in lipid peroxidation, an indicator of oxidative stress, persisting through worm development. Three lines of evidence provided support for the behavioural avoidance hypothesis. First, shoal area decreased in groups of minnows exposed to O. ptychocheilus cercariae compared to those exposed to cues from other aquatic threats. Second, average worm numbers were 50 % lower in fish confined to artificial shoals compared to non-shoaling minnows, indicating that shoaling reduces risk of exposure. The third experiment showed that minnows within the centre of shoal reduced their risk of infection by 67%. Taken together, these results demonstrate a cost of trematode infection on minnows, that minnows can detect infective larvae within the water column, and that social living reduces a hosts’ risk of exposure. / xi, 84 leaves : ill. ; 29 cm

The relationships among parasite growth, responses to infection and host genetic factors were examined in rodents infected with Echinococcus multilocularis. Mongolian gerbils, cotton rats and C57L/J mice were relatively susceptible to the infection, whereas five other inbred strains of mice, and hybrids and backcrosses between C57L/J and C57BL/6J mice were more resistant. In mice, susceptibility to E. multilocularis was controlled by multiple, non-H-2-linked genes, as were pathological, inflammatory and specific (antibody) responses to the infection. These responses were also affected by the degree of parasite growth in individual hosts. Antibodies, natural killer cells and hematological responsiveness were ruled out as contributing to resistance to E. multilocularis. Studies on peritoneal leukocytes from infected animals suggested that infections with E. multilocularis were controlled by cells in two phases: an acute phase involving neutrophils and mononuclear cells and a chronic phase involving eosinophils and mononuclear cells.