Browsing by Author "Van Daalen, Corne E."

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    Effects of within-generation thermal history on the flight performance of Ceratitis capitata : colder is better
    (The Company of Biologists, 2014-07) Esterhuizen, Nanike; Clusella-Trullas, Susana; Van Daalen, Corne E.; Schoombie, Ruben E.; Boardman, Leigh; Terblanche, John S.
    The influence of thermal history on temperature-dependent flight performance was investigated in an invasive agricultural pest insect, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at these temperatures (Ttest) as adults using a full-factorial study design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Successful flight performance increased with increasing Ttest across all acclimation groups (from 10% at 15°C to 77% at 30°C). Although Tacc did not affect flight performance independently, it did have a significant interaction effect with Ttest. Multiple comparisons showed that flies which had been acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures, but warm-acclimated flies did not outperform cold-acclimated flies at warmer temperatures. This provides partial support for the ‘colder is better’ hypothesis. To explain these results, several flight-related traits were examined to determine whether Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase enzyme activity. Although significant effects of Tacc could be detected in several of the traits examined, with an emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any of these traits. Overall, these results are important for understanding dispersal physiology despite the fact that the mechanisms of acclimation-related changes in flight performance remain unresolved.
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    High metabolic and water-loss rates in caterpillar aggregations : evidence against the resource-conservation hypothesis
    (Company of Biologists, 2013) Schoombie, Ruben E.; Boardman, Leigh; Groenewald, Berlize; Glazier, Douglas S.; Van Daalen, Corne E.; Clusella-Trullas, Susana; Terblanche, John S.
    Several hypotheses have been proposed for explaining animal aggregation, including energy or water conservation. However, these physiological hypotheses have not been well investigated. Here, we report the effects of aggregation on metabolic (Embedded Image) and evaporative water-loss rates (Embedded Image) of the gregarious caterpillar Eutricha capensis, by comparing individuals and groups of individuals (N=10–100). Contrary to findings from previous physiological studies, we did not find an advantage to aggregation: unexpectedly, Embedded Image and Embedded Image did not decrease with increasing group size. Embedded Image and Embedded Image generally remained constant or increased in larger groups relative to individuals. The amount of water lost per unit of CO2 exchanged (Embedded Image: Embedded Image ratio) showed a marked increase in grouped caterpillars, particularly in larger groups. Other benefits of aggregation (e.g. reduced predation or increased growth rates) likely outweigh these potential costs, because individuals of E. capensis aggregate voluntarily despite no obvious energetic or hygric advantage, and other potentially confounding group effects (e.g. increased thermoregulatory advantage or whole-animal activity) are inconsequential. The results of this study provide an important exception to physiological studies reporting enhanced energy or water conservation in animal groups.
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    Strategies for the control of a satellite with thruster misalignment
    (Stellenbosch : University of Stellenbosch, 2006-03) Van Daalen, Corne E.; Treurnicht, J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    This project investigates two problems related to satellites that contain cold gas thrusters and reaction wheels. The first problem concerns the estimation of the thruster force response to a pulse command. An optimal data integration method is developed and implemented to estimate the thruster force output from a number of noisy sensors. The second problem occurs when the output force vector of a thruster mounted on a satellite is misaligned with the centre of mass with the satellite. As a result a disturbance torque is generated on the satellite during thruster operation.