Thèse de doctorat : Langues et littératures germaniques et scandinaves : Nancy 2 : 2007. Thèse de doctorat : Langues et littératures germaniques et scandinaves : Université d'Heidelberg : 2007. / Titre provenant de l'écran-titre.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

When an individual interacts socially with a conspecific, their behavioural phenotype is affected directly by their genotype (‘direct genetic effect’, DGE), but may also be affected indirectly by the genotype of the opposing individual (‘indirect genetic effect’, IGE). While there is no doubt that IGEs occur in various organisms and contexts, it is unknown how properties of the environment may influence the relative magnitude of DGEs, IGEs, and their covariance. To gain insight into this, I examined territorial interactions in Drosophila melanogaster. Due to their short generation time and relatively simple care requirements, D. melanogaster has been used extensively in quantitative genetic research. Using offspring from a half-sib breeding design, I constructed an arena for documenting multiple dyadic territoriality assays with two sizes of a food resource. With this apparatus, 618 territoriality contests between 1,236 individuals were recorded and scored for four key aggressive behaviours. The results revealed significant genetic variation in how opponent effects on focal individuals changed between environments (i.e., genetic variation in the plasticity of IGEs). In addition, changes in DGEs and IGEs between environments were strongly and positively correlated (i.e., there was a DGE × IGE × environment interaction), although confirmation of this result in further studies is warranted because it was non-significant (P = 0.10), likely due to large uncertainties arising in part from some small variance component estimates. As a high throughput system for quantify IGEs in territoriality in Drosophila, my approach holds promise but there are issues to resolve, including automating phenotyping behaviors in place of manual scoring to enable many more trials. Additionally, modifications to increase humidity during trials might result in increased expression of certain territorial behaviours.

Many applications for unmanned vehicles involve autonomous interaction between two or more craft, and therefore, relative navigation is a key issue to explore. Several high fidelity hardware simulations exist to produce accurate dynamics. However, these simulations are restricted by size, weight, and power needed to operate them. The use of a small Unmanned Ground Vehicle (UGV) for the relative navigation problem is investigated. The UGV has the ability to traverse large ranges over uneven terrain and into varying lighting conditions which has interesting applications to relative navigation. The basic problem of a vehicle following another is researched and a possible solution explored. Statistical pressure snakes are used to gather relative position data at a specified frequency. A cubic spline is then fit to the relative position data using a least squares algorithm. The spline represents the path on which the lead vehicle has already traversed. Controlling the UGV onto this relative path using a sliding mode control, allows the follow vehicle to avoid the same stationary obstacles the lead vehicle avoided without any other sensor information. The algorithm is run on the UGV hardware with good results. It was able to follow the lead vehicle around a curved course with only centimeter-level position errors. This sets up a firm foundation on which to build a more versatile relative motion platform. / Master of Science

Doctor of Philosophy / Department of Statistics / Gary Gadbury / Researches in the fields in science and statistics often go beyond the two-variable cause-and-effect relationship, and also try to understand what connects the causal relationship and what changes the magnitude or direction of the causal relationship between two variables, predictor(T) and outcome (Y). A mediator (Z) is a third variable that links a cause and an effect, whereby T causes the Z and Z causes Y. In general, a given variable may be said to function as a mediator to the extent that it accounts for the relation between the predictor and the outcome (Baron and Kenny, 1986). The initial question regards the appropriate characterization of a mediation effect. Most studies, when comparing one or more treatments focus on an average mediating effect. This average mediating effect can be misleading when the mediating effects vary from subject to subject in the population. The primary focus of this research is to investigate individual mediating effects in a population, and to define a variance of these individual mediating effects. A concept called subject-mediator (treatment) interaction is presented and its role in evaluating a mediator’s behavior on a population of units is studied. This is done using a framework sometimes called a counterfactual model. Some common experimental designs that provide different knowledge about this interaction term are studied. The subgroup analysis is the most common analytic approach for examining heterogeneity of mediating effects. In mediation analysis, situations can arise where Z and Y cannot both be measured on an individual unit. We refer to such data as terminal measures data. We show a design where a mediating effect cannot be estimated in terminal measures data and another one where it can be, with an assumption. The assumption is linked to the idea of pseudo-replication. These ideas are discussed and a simulation study illustrates the issues involved when analyzing terminal measures data. We know of no methods that are currently available that specifically address terminal measures data.

Maize, a genetically diverse crop, is the third largest cereal crop in the world and the most important staple cereal in sub-Saharan Africa, supplying 50% of the calorie intake in this region. The stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a key constraint to cereal production in most resource-poor smallholder farming systems in sub-Saharan Africa causing crop losses accruing up to 88%. Previous studies have shown that feeding by herbivorous insects induces maize to emit volatiles attractive to natural enemies. However, these antagonists are recruited when damage has already been inflicted on the plant. Recent investigations revealed that egg deposition can induce maize landraces of Mesoamerican origin to emit volatiles attractive to C. partellus parasitoids, a trait previously reported to be absent in maize hybrids. However, genotypic variation in this indirect defence trait within maize varieties adapted to local agroclimatic conditions and the effect of processes such as domestication and breeding on this trait are not known. Moreover, it is not known whether maize varieties possessing this indirect defence trait can directly deter further herbivore colonization and constitutively suppress the herbivore‟s larval development or whether they can induce the same defence trait in neighbouring unattacked plants. This study sought to fill these knowledge gaps with the aim of exploiting these plant defence traits in the development of ecologically sound crop protection strategies. Experiments were conducted in which headspace volatile samples were collected from plants of wild, landrace and hybrid maize with and without C. partellus eggs. Chemical analyses were done using gas chromatography (GC), coupled GC-mass spectrometry (GC-MS) and coupled GC-Electroantenography (GC-EAG). Behavioural bioassays were done using egg (Trichogramma bournieri Pintureau (Hymenoptera: Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids in a 4-arm olfactometer using volatiles collected from the plants. Moreover, C. partellus larval preference, growth and development as well as subsequent oviposition behaviour of gravid C. partellus moths on these plants were determined. Behavioural assays showed that both T. bournieri and C. sesamiae preferred volatiles from four of the five wild teosinte species, five landraces and one of two maize hybrids exposed to egg deposition. Similarly, volatiles collected from unoviposited maize landrace plants exposed to oviposited landrace maize plants emitting oviposition-induced volatiles, were attractive to both egg and larval parasitoids. Moreover, maize varieties emitting these oviposition-induced volatiles deterred further herbivore colonization and suppressed larval development. Volatile analysis by GC and GC-MS revealed marked increases in volatile emission as well as qualitative changes in the odour blends in four wild types, five landraces and one hybrid, following stemborer oviposition. Coupled GC-EAG analysis of attractive samples revealed that C. sesamiae was responsive to (E)-2- hexenal, (Z)-3-hexen-1-ol, nonane, 6-methyl-5-heptene-2-one, α-pinene, myrcene, limonene, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, 3,4-dimethylacetophenone and (E)-β-farnesene. Results from this study provide insights into tritrophic interactions thus paving the way for designing novel and ecologically sound pest management strategies through breeding crops with this novel oviposition-induced defence trait. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Maize, a genetically diverse crop, is the third largest cereal crop in the world and the most important staple cereal in sub-Saharan Africa, supplying 50% of the calorie intake in this region. The stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a key constraint to cereal production in most resource-poor smallholder farming systems in sub-Saharan Africa causing crop losses accruing up to 88%. Previous studies have shown that feeding by herbivorous insects induces maize to emit volatiles attractive to natural enemies. However, these antagonists are recruited when damage has already been inflicted on the plant. Recent investigations revealed that egg deposition can induce maize landraces of Mesoamerican origin to emit volatiles attractive to C. partellus parasitoids, a trait previously reported to be absent in maize hybrids. However, genotypic variation in this indirect defence trait within maize varieties adapted to local agroclimatic conditions and the effect of processes such as domestication and breeding on this trait are not known. Moreover, it is not known whether maize varieties possessing this indirect defence trait can directly deter further herbivore colonization and constitutively suppress the herbivore‟s larval development or whether they can induce the same defence trait in neighbouring unattacked plants. This study sought to fill these knowledge gaps with the aim of exploiting these plant defence traits in the development of ecologically sound crop protection strategies. Experiments were conducted in which headspace volatile samples were collected from plants of wild, landrace and hybrid maize with and without C. partellus eggs. Chemical analyses were done using gas chromatography (GC), coupled GC-mass spectrometry (GC-MS) and coupled GC-Electroantenography (GC-EAG). Behavioural bioassays were done using egg (Trichogramma bournieri Pintureau (Hymenoptera: Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids in a 4-arm olfactometer using volatiles collected from the plants. Moreover, C. partellus larval preference, growth and development as well as subsequent oviposition behaviour of gravid C. partellus moths on these plants were determined. Behavioural assays showed that both T. bournieri and C. sesamiae preferred volatiles from four of the five wild teosinte species, five landraces and one of two maize hybrids exposed to egg deposition. Similarly, volatiles collected from unoviposited maize landrace plants exposed to oviposited landrace maize plants emitting oviposition-induced volatiles, were attractive to both egg and larval parasitoids. Moreover, maize varieties emitting these oviposition-induced volatiles deterred further herbivore colonization and suppressed larval development. Volatile analysis by GC and GC-MS revealed marked increases in volatile emission as well as qualitative changes in the odour blends in four wild types, five landraces and one hybrid, following stemborer oviposition. Coupled GC-EAG analysis of attractive samples revealed that C. sesamiae was responsive to (E)-2- hexenal, (Z)-3-hexen-1-ol, nonane, 6-methyl-5-heptene-2-one, α-pinene, myrcene, limonene, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, 3,4-dimethylacetophenone and (E)-β-farnesene. Results from this study provide insights into tritrophic interactions thus paving the way for designing novel and ecologically sound pest management strategies through breeding crops with this novel oviposition-induced defence trait. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

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Harry Potter-series are widely popular fantasy-novels that have influenced young readers all over the world on various issues, one being gender. Many arguments have been proposed to explain how the Harry Potter-series has a gender-biased attitude. Although previous research has covered a wide variety of claims, this essay will focus on examining the language and word choices made to describe the male and female characters of Harry Potter and the Philosopher’s Stone and Harry Potter and the Goblet of Fire. The word choices consist of both traditionally masculine adjectives and verbs as well as adjectives and verbs with negative connotations. To obtain a comprehensive view of the gender-biased tone of the two novels, the essay will not only examine the language, but also investigate if there is a gender-biased way of portraying the characters based on how their behaviour is described. These observations will be combined with previous research which includes Sara Mills’ investigation of sexist language and indirect sexism, Heilman and Donaldson’s critical perspective on the Harry Potter-novels, and Turner-Bowker’s study of stereotyping in young readers’ literature. These studies support my arguments and show that that there is a gender-bias in the way the characters are described, both through language and in the way that the character’s act in Harry Potter and the Philosopher’s Stone and Harry Potter and the Goblet of Fire.