En utilisant comme cas d’étude le mouflon Méditerranéen (Ovis gmelini musimon × Ovis sp.), les objectifs de cette thèse étaient de mieux comprendre comment sont liés diversité génétique, comportement des individus, flux de gènes et dynamique parasitaire. Au travers d’approches de génétique des populations et de génétique du paysage, nous avons pu mettre en évidence que la structure génétique spatiale de la population étudiée était impactée par son histoire d’introduction, sa structure socio-spatiale et le paysage dans lequel elle évolue. Etant donné l’impact de ces divers éléments sur les flux de gènes des mouflons, nous nous attendions à ce qu’ils déterminent également les flux de parasites dans la population. Nos résultats ont, au contraire, révélé que les parasites circulent mieux que les gènes de mouflons dans la population. Enfin, nous avons montré que les capacités de résistance des hôtes face à leurs parasites dépendaient de la diversité génétique neutre et adaptative, notamment de l’hétérozygotie d’un gène lié à l’immunité. Les résultats de ce travail décrivent avec précision la distribution de la variabilité génétique et son lien avec les risques sanitaires dans la population d’étude, apportant ainsi des informations cruciales pour la mise en place de stratégies de gestion et de conservation des populations de mouflons dans le contexte actuel de changements globaux et de réémergences de maladies. / Using as a case study the Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.), we aimed at better understanding how are linked genetic diversity, individual behaviour, gene flows and parasitic dynamic. Using population and landscape genetics approaches, we showed that the spatial genetic structure of the studied population was determined by its introduction history, its socio-spatial structure and the landscape in which it evolves. Given the impact of these elements on mouflon gene flow, we expected them to also determine parasite transmission in the population. Our results nevertheless evidenced that parasite are better dispersed than mouflon genes. Finally, we showed that host resistance to parasites depends on neutral and adaptive genetic diversity, and more specifically on heterozygosity at a immunity-linked locus. Our results precisely describe genetic variability spatial distribution and its link with sanitary risks in the studied population, bringing crucial information for wild sheep population management and conservation in the current context of global changes and disease reemergence.

Dentre os parasitoides utilizados no controle biológico de pragas está Habrobracon hebetor Say, 1857 (Hymenoptera: Braconidae), um ectoparasitoide frequentemente encontrado em armazéns de grãos e que parasita espécies de lepidópteros que atacam produtos armazenados. Dada a sua agressividade e pela sua ação em laboratório é um potencial agente de controle biológico de diversas espécies de lagartas que causam prejuízos econômicos. Portanto, no presente trabalho buscou-se avaliar o potencial de parasitismo de H. hebetor, parasitoide já existente no Brasil, sobre diferentes pragas agrícolas pertencentes às famílias Noctuidae (9 espécies), Erebidae e Crambidae, em relação à duas espécies de Pyralidae (controles), com base na paralisação e no tempo de tal paralisação em lagartas de diferentes tamanhos, com diferentes densidades do parasitoide, bem como seu desenvolvimento nas espécies escolhidas pelo potencial observado. Foram estudadas as espécies Anagasta kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae) (controle 1), Corcyra cephalonica (Staiton, 1865) (Lepidoptera: Pyralidae) (controle 2), Helicoverpa armigera (Hübner, 1809) (Lepidoptera: Noctuidae), Chloridea virescens (Fabricius, 1777) (Lepidoptera: Noctuidae), Spodoptera cosmioides (Walker, 1858) (Lepidoptera: Noctuidae), Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), Chrysodeixis includens (Walker, 1858) (Lepidoptera: Noctuidae), Spodoptera albula (Walker, 1857) (Lepidoptera: Noctuidae), Spodoptera eridania (Cramer, 1782) (Lepidoptera: Noctuidae), Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), Helicoverpa zea (Boddie, 1850) (Lepidoptera: Noctuidae), Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Erebidae), Agrotis ipsilon (Hufnagel, 1767) (Lepidoptera: Noctuidae). Foram avaliados o tempo e a porcentagem de paralisação das lagartas, assim como a correlação dessas variáveis com o tamanho do hospedeiro (2º ou 4º ínstar) e o número de parasitoides (1, 2 e 4), sendo as espécies mais paralisadas e no menor tempo, selecionadas como melhores por meio de uma análise de componentes principais. Estudou-se a preferência do parasitoide sobre as melhores espécies de lagartas por meio de um teste de livre escolha, observando-se a paralisação e o tempo gasto para tal paralisação. Avaliou-se o efeito da densidade de lagartas na paralisação por H. hebetor durante 4 dias. Posteriormente foi realizada a biologia das espécies selecionadas avaliando-se a duração dos estágios evolutivos assim como a viabilidade das melhores espécies e o número de ovos colocados em 3 dias. Não houve relação entre a paralisação e o parasitismo por H. hebetor. Quanto maior a paralisação do hospedeiro, menor foi o tempo para tal paralisação. O número de parasitoides e os ínstares mais avançados reduziram significativamente o tempo de paralisação. Houve grande variação na paralisação entre as espécies das 3 famílias estudadas (Noctuidae, Erebidae, Crambidae) e dentro de uma mesma espécie. Das três espécies selecionadas com base na paralisação, S. cosmioides, A. ipsilon e D. saccharalis, apenas esta última se apresentou como potencial hospedeiro para parasitismo de H. hebetor. Existe um potencial de utilização de H. hebetor no controle de D. saccharalis, com base nos resultados obtidos, exigindo uma validação em condições de campo. / Among the parasitoids used in biological pest control is Habrobracon hebetor Say, 1857 (Hymenoptera: Braconidae), an ectoparasitoid often found in grain stores and parasitizing lepidopteran species that attack stored products. Given its aggressiveness and its action in the laboratory is a potential agent of biological control of several species of caterpillars that cause economic losses. Therefore, the present work aimed to evaluate the parasitism potential of H. hebetor, a parasitoid already present in Brazil, on different agricultural pests belonging to the families Noctuidae (9 species), Erebidae and Crambidae, in relation to 2 Pyralidae species as control, based on the paralyzation and the time of such paralysis in caterpillars of different sizes, with different parasitoid densities, as well as their development in the species with potential. The species studied were: Anagasta kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae) (control 1), Corcyra cephalonica (Staiton, 1865) (Lepidoptera: Pyralidae) (control 2), Helicoverpa armigera (Hübner, 1809) (Lepidoptera: Noctuidae) , Chloridea virescens (Fabricius, 1777) (Lepidoptera: Noctuidae), Spodoptera cosmioides (Walker, 1858) (Lepidoptera: Noctuidae), Spodoptera frugiperda (JE Smith, 1797) (Lepidoptera: Noctuidae), Chrysodeixis includens (Lepidoptera: Noctuidae), Spodoptera albula (Walker, 1857) (Lepidoptera: Noctuidae), Spodoptera eridania (Cramer, 1782) (Lepidoptera: Noctuidae), Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), Helicoverpa zea (Boddie, 1850) (Lepidoptera: Noctuidae), Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Erebidae), Agrotis ipsilon (Hufnagel, 1767) (Lepidoptera: Noctuidae). The time and percentage of caterpillar paralysis were evaluated, as well as the correlation of these variables with the host size (2nd or 4th instar) and the number of parasitoids (1, 2 and 4), with the species being more paralyzed and, in less time, selected as the best by means of a principal component analysis. The preference of the parasitoid on the best caterpillar species was studied by means of a free choice test, observing the paralyzation and the paralyzation time. The effect of caterpillar density on H. hebetor paralyzation was evaluated for 4 days. Afterwards the biology of the selected species was evaluated, evaluating the duration of the evolutionary stages as well as the viability of the best species and the number of eggs placed in 3 days. There was no relationship between paralyzation and parasitism by H. hebetor. The greater the host paralysis, the longer the paralyzation delay. The number of parasitoids and the more advanced instars significantly reduced the standstill time. There was a great variation of paralysis among the species of the three families studied (Noctuidae, Erebidae, Crambidae) and within the same species. The three species selected based on the paralyzation, S. cosmioides, A. ipsilon and D. saccharalis, only the sugarcane borer presented as a potential host for H. hebetor parasitism. There is a potential of using H. hebetor in the control of D. saccharalis, based on the results obtained, requiring validation under field conditions.

Bibliography: leaves 113-128 / xii, 128, [63] leaves, [6] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology and Immunology, 1984

Bibliography: leaves 111-137.

Calow (1983) realized that differences between parasites and their free-living relatives can be explained by the differences in nutrient richness. I propose a model that is based on Calow's idea which identifies the relative position of different trophic strategies (e.g. predation, grazing, parasitism and others) based on (1) the differences by which consumers arrive at their intrinsic rate of growth, and (2) the ecological impact they inflict on their hosts. I hypothesize that trophic interactions can be clarified if a parameter is included that takes into account the host's/prey's fate in the interaction. Moreover, this model suggests specific trophic evolutionary pathways (TEPs) between each strategy, and suggests that some pathways are more likely than others. In particular, parasitoidism is believed to be a highly derived strategy, and the TEPs presented in the model suggest parasitoidism could have arisen from either a predator-like or a typical-parasitic ancestor. Though the trophic categories determined by the model seem intuitive, this approach does provide, apparently for the first time, an objective, mathematically and ecologically useful basis for classifying animal trophic relationships. / Graduation date: 1998

Morella cerifera (L.) Small, the Wax Myrtle, forms both arbuscular mycorrhizas and cluster roots which generally are regarded as alternative adaptations for phosphorus acquisition. But whether or not arbuscular mycorrhizal fungi (AMF) provide any benefit to M. cerifera is not known. Nevertheless, AMF can proliferate extensively within the litter leaves that accumulate beneath M. cerifera. The main objective of this study was to determine if AMF are beneficial to M. cerifera host plants in the presence of leaf litter. In the field, I examined leaf traits that affect the colonization of leaf litter by AMF. I compared AMF colonization of labile versus recalcitrant leaves, and that of leaf pieces with obstructed versus non-obstructed veins. In pot experiments, I examined if labile or recalcitrant litter influences the potential benefit of AMF to M. cerifera, and if nitrogen (N) or phosphorus (P) fertilization influences that benefit in the presence of recalcitrant leaf litter. I found that AMF extensively colonize both labile and recalcitrant leaves, but that they colonize labile leaves more rapidly than recalcitrant leaves. I found significantly less colonization in leaf pieces with obstructed veins than in those with non-obstructed veins which suggests that penetration by the fungi primarily is mechanical and not enzymatic. The pot experiments showed that AMF are parasitic on M. cerifera except when recalcitrant leaf litter is present, and that the effects of AMF on M. cerifera are indirect and mediated through effects of AMF on N-fixing nodule dry weight. In both pot experiments, AMF enhanced litter decomposition and may have enhanced plant P-nutrition. AMF benefited M. cerifera growth in the absence of N fertilization but negatively affected M. cerifera growth when N was added. In the presence of litter, inoculation with AMF increased cluster root formation, suggesting that these two adaptations may be complementary in extremely nutrient-poor soils. Overall, this study shows that M. cerifera does benefit from association with AMF, and it suggests that AMF play a more important role in the acquisition of mineral nutrients from leaf litter than previously recognized.

Thelohania solenopsae are intracellular pathogens found in the red imported fire ant, Solenopsis invicta. These pathogens cause detrimental effects to their fire ant hosts. The present study revealed that the midgut and the meconium materials from pupating fourth instar larvae were possible vehicles for the horizontal transmission of the disease. The pathogen was further found to cause a reduction of humeral proteins. In SDS-PAGE stained with silver, several proteins were observed only in controls but not in infected fire ant queens. Different queens were found to have variable proteins reduced due to infection of this pathogen. Furthermore, vitellogenin titers were found to be significantly reduced in infected fire ant queens, although the infection rates of the fat body cells was found to be less than 20%. Finally, although the pathogens did not directly induce apoptosis in infected cells, there were more infected cells undergoing apoptosis than uninfected cells. There was no evidence to support the idea that infected fat body cells became more resistant to apoptosis inducers.

The adaptive evolutionary potential of a species or population to cope with omnipresent environmental challenges is based on its genetic variation. Variability at immune genes, such as the major histocompatibility complex (MHC) genes, is assumed to be a very powerful and effective tool to keep pace with diverse and rapidly evolving pathogens. In my thesis, I studied natural levels of variation at the MHC genes, which have a key role in immune defence, and parasite burden in different small mammal species. I assessed the importance of MHC variation for parasite burden in small mammal populations in their natural environment. To understand the processes shaping different patterns of MHC variation I focused on evidence of selection through pathogens upon the host. Further, I addressed the issue of low MHC diversity in populations or species, which could potentially arise as a result from habitat fragmentation and isolation. Despite their key role in the mammalian evolution the marsupial MHC has been rarely investigated. Studies on primarily captive or laboratory bred individuals indicated very little or even no polymorphism at the marsupial MHC class II genes. However, natural levels of marsupial MHC diversity and selection are unknown to date as studies on wild populations are virtually absent. I investigated MHC II variation in two Neotropical marsupial species endemic to the threatened Brazilian Atlantic Forest (Gracilinanus microtarsus, Marmosops incanus) to test whether the predicted low marsupial MHC class II polymorphism proves to be true under natural conditions. For the first time in marsupials I confirmed characteristics of MHC selection that were so far only known from eutherian mammals, birds, and fish: Positive selection on specific codon sites, recombination, and trans-species polymorphism. Beyond that, the two marsupial species revealed considerable differences in their MHC class II diversity. Diversity was rather low in M. incanus but tenfold higher in G. microtarsus, disproving the predicted general low marsupial MHC class II variation. As pathogens are believed to be very powerful drivers of MHC diversity, I studied parasite burden in both host species to understand the reasons for the remarkable differences in MHC diversity. In both marsupial species specific MHC class II variants were associated to either high or low parasite load highlighting the importance of the marsupial MHC class II in pathogen defence. I developed two alternative scenarios with regard to MHC variation, parasite load, and parasite diversity. In the ‘evolutionary equilibrium’ scenario I assumed the species with low MHC diversity, M. incanus, to be under relaxed pathogenic selection and expected low parasite diversity. Alternatively, low MHC diversity could be the result of a recent loss of genetic variation by means of a genetic bottleneck event. Under this ‘unbalanced situation’ scenario, I assumed a high parasite burden in M. incanus due to a lack of resistance alleles. Parasitological results clearly reject the first scenario and point to the second scenario, as M. incanus is distinctly higher parasitised but parasite diversity is relatively equal compared to G. microtarsus. Hence, I suggest that the parasite load in M. incanus is rather the consequence than the cause for its low MHC diversity. MHC variation and its associations to parasite burden have been typically studied within single populations but MHC variation between populations was rarely taken into account. To gain scientific insight on this issue, I chose a common European rodent species. In the yellow necked mouse (Apodemus flavicollis), I investigated the effects of genetic diversity on parasite load not on the individual but on the population level. I included populations, which possess different levels of variation at the MHC as well as at neutrally evolving genetic markers (microsatellites). I was able to show that mouse populations with a high MHC allele diversity are better armed against high parasite burdens highlighting the significance of adaptive genetic diversity in the field of conservation genetics. An individual itself will not directly benefit from its population’s large MHC allele pool in terms of parasite resistance. But confronted with the multitude of pathogens present in the wild a population with a large MHC allele reservoir is more likely to possess individuals with resistance alleles. These results deepen our understanding of the complex causes and processes of evolutionary adaptations between hosts and pathogens. / In einer sich ständig verändernden Umwelt ist es unverzichtbar, sich fortwährend zu verändern und anzupassen. Dabei gründet sich das Anpassungsvermögen oder das evolutionäre Potential einer Art auf ihre genetische Variabilität. In der Krankheitsabwehr ist die Variabilität der Immungene ein besonders wichtiges und effektives Instrument, weil Pathogene sehr vielfältig sind und schnell evolvieren. Im Rahmen meiner Doktorarbeit habe ich mich mit der Variabilität des Immungen-Komplexes MHC (major histocompatibility complex) beschäftigt, der eine Schlüsselrolle in der Immunabwehr bei Vertebraten einnimmt. Anhand verschiedener Arten und Populationen von Kleinsäugern habe ich den Einfluss der MHC Vielfalt auf den Parasitenbefall unter natürlichen Bedingungen untersucht. Dabei interessierte mich insbesondere das Vorkommen geringer MHC Variabilität in Populationen, das möglicherweise eine Folge von Lebensraum-fragmentierung und Isolation ist. Obwohl Beuteltiere eine zentrale Rolle in der Evolution der Säugetiere spielen, ist über ihren MHC bislang nur sehr wenig bekannt. Einige Studien befassten sich mit Labor- oder Zootieren, und deuteten auf geringe oder sogar gar keine Variation im MHC Klasse II bei Beuteltieren hin. Allerdings gab es bislang nahezu keine Studien an frei lebenden Beuteltieren, deshalb war bislang ein natürliches Ausmaß der MHC Variabilität unbekannt. Anhand von zwei endemischen neotropischen Beuteltieren aus dem brasilianischen Küstenregenwald (Gracilinanus microtarsus, Marmosops incanus) habe ich überprüft, ob sich diese geringe MHC Vielfalt unter natürlichen Freilandbedingungen bestätigt. Erstmals konnte ich zeigen, dass der MHC II bei Beuteltieren charakteristische Merkmale positiver Selektion aufweist, die bisher nur von placentalen Säugern, Vögeln und Fischen bekannt waren: Positive Selektion auf spezifischen Aminosäurepositionen, Rekombination und Trans-Species-Polymorphismus. Darüber hinaus unterschieden sich die beiden Beuteltierarten beträchtlich in ihrer MHC II Variabilität. Während M. incanus sich als relativ wenig divers erwies, zeigte G. microtarsus eine zehnmal höhere Vielfalt und widerlegt damit die generelle Gültigkeit der ursprünglich angenommenen geringen MHC II Variabilität bei Beuteltieren. Um diese beachtlichen Diversitätsunterschiede zwischen den beiden Arten zu erklären, habe ich die Parasitenbelastung untersucht. Bei beiden Arten konnte ich nachweisen, dass bestimmte MHC Varianten mit entweder hoher oder niedriger Parasitenbelastung verknüpft waren. Solche Assoziationen spiegeln Pathogen-vermittelte Selektion wider, untermauern die Funktionalität des MHC Klasse II bei Beuteltieren und weisen auf dieselbe Bedeutsamkeit des MHC wie bei placentalen Säuger, Vögeln und Fischen hin. Ich entwickelte zwei alternative evolutionäre Szenarien, unter denen eine geringe MHC Variabilität denkbar ist. Im Szenario des ‘evolutionären Gleichgewichts’ ist geringe MHC Variabilität die Folge eines verminderten Selektionsdruckes durch wenige Parasiten, sodass eine geringe Parasitendiversität zu erwarten ist. Alternativ könnte eine geringe MHC Variabilität aber auch Folge eines kürzlich erlittenen Verlustes an genetischer Variabilität sein, beispielsweise durch ein Flaschenhalsereignis. Unter diesem Szenario des ‘Ungleichgewichts’ wäre bei M. incanus im Falle eines potentiellen Verlustes von Resistenzallelen eine starke Parasitenbelastung zu erwarten. Die parasitologischen Ergebnisse widersprechen dem ersten und deuten eher auf das zweite Szenario. M. incanus war deutlich stärker parasitiert als G. microtarsus, wohingegen die Parasitendiversität bei beiden Arten ungefähr gleich war. Die hohe Parasitenbelastung bei M. incanus ist offenbar weniger der Auslöser als vielmehr eine Folge seiner geringen MHC Vielfalt zu sein. Üblicherweise werden sowohl die Variabilität des MHC als auch seine Verknüpfung mit Parasitenbelastung innerhalb von einzelnen Populationen untersucht, nur selten wird die Variation zwischen Populationen in Betracht gezogen. Um Erkenntnisse auf dieser Ebene zu gewinnen, habe ich den Zusammenhang zwischen genetischer Vielfalt und Parasitenbelastung nicht auf der Ebene des Individuums, sondern auf der Populationsebene anhand der europäischen Gelbhalsmaus (Apodemus flavicollis) erforscht. Dabei wurden Populationen mit unterschiedlicher genetischer Variabilität am MHC und an neutralen genetischen Markern (Mikrosatelliten) betrachtet. Ich konnte nachweisen, dass Populationen, die über ein großes Spektrum verschiedener MHC Allele verfügen, besser gegen starke Parasitenbelastung gewappnet sind als Populationen mit einer geringen Anzahl MHC Allele. In einer MHC-diversen Population ist die Gegenwart von Individuen mit Resistenzallelen deutlich wahrscheinlicher, und damit die Überlebenswahrscheinlichkeit der Population. Diese Ergebnisse erweitern und vertiefen unsere Erkenntnisse zu die komplexen evolutionären Vorgängen und Mechanismen zwischen Wirt und Parasit in ihrem fortwährenden Wettstreit.

Thelohania solenopsae are intracellular pathogens found in the red imported fire ant, Solenopsis invicta. These pathogens cause detrimental effects to their fire ant hosts. The present study revealed that the midgut and the meconium materials from pupating fourth instar larvae were possible vehicles for the horizontal transmission of the disease. The pathogen was further found to cause a reduction of humeral proteins. In SDS-PAGE stained with silver, several proteins were observed only in controls but not in infected fire ant queens. Different queens were found to have variable proteins reduced due to infection of this pathogen. Furthermore, vitellogenin titers were found to be significantly reduced in infected fire ant queens, although the infection rates of the fat body cells was found to be less than 20%. Finally, although the pathogens did not directly induce apoptosis in infected cells, there were more infected cells undergoing apoptosis than uninfected cells. There was no evidence to support the idea that infected fat body cells became more resistant to apoptosis inducers.

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