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Body size affects rates of most biological and ecological processes, from individual performance to ecosystem function. Within species, emergent body size patterns have been formalised into prominent biogeographical and biological rules, including James' Rule (larger individuals are found at higher, colder latitudes), and the Temperature-Size Rule (individuals reared in warmer conditions grow to a smaller adult size). Body size also varies seasonally and with altitude. Yet, the patterns and drivers of these size gradients, and the degree to which they co-vary and share explanatory mechanisms, have never been systematically evaluated. We undertake the most comprehensive metaanalyses to date of temperature- and biogeographical-size clines within arthropod species. Aquatic species show greater reductions in body size with warming and decreasing latitude compared to terrestrial species, likely an adaptive response to deal with increased metabolic demand in the warm and the greater difficulty to uptake oxygen in water than in air. Voltinism explains variation in laboratory temperature- and latitudinal-size clines in terrestrial species. While size decreases with warming and with decreasing latitude in multivoltine terrestrial arthropods, size increases on average in univoltine species, consistent with predictions from size vs. season-length trade-offs. In the globally distributed sub-class Copepoda, seasonal temperature-size (T-S) gradients differ between current-feeding calanoids and ambush-feeding cyclopoids, suggesting that differences in the size- and temperature-dependence of alternative feeding strategies may influence the T-S response. Finally, through experimentation, we explore the progression of the T-S response of Copepoda during ontogeny. The T-S response is more strongly generated in particular life stages, and even reduced in some periods, providing evidence that the temperature-dependence of growth and developmental rates is modified during ontogeny. Ultimately, close similarities between T-S responses measured in controlled laboratory conditions, and seasonal and biogeographical size clines in the field across different arthropod taxa, suggests that these patterns share similar selective pressures.

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Current bioinformatic methods such as molecular phylogenetics and phylogenomics provide us with good insight to symbiont evolution. Though modern science evolves rapidly, accelerates speed of acquiring novel discoveries and improves their quality, there is still endless row of questions waiting to be answered. This thesis focuses on origins of symbiosis between insects and Enterobacteria, and the mechanisms promoting association of bacteria with arthropods. The main emphasis is put on the secondary symbionts of the genus Sodalis (Enterobacteriaceae) and the pathogenic Anaplasma phagocytophilum (Anaplasmataceae) that seems to be undergoing first steps to become hereditary mutualist.

Human activities have dramatically altered the functioning of ecosystems through the ages. Urbanization illustrates the effect of anthropogenic activity by the transformation of natural areas to ecologically disturbed regions (development of towns, cities and settlements). The growing need for urban employment in South Africa has led to an increase in the number of informal settlements on the periphery of urban areas. These settlements result in fragmentation and sprawling of cities, which intensifies strain on the natural environment. Fragmentation in urban regions then leads to the formation of 'patches' of land which exhibit different disturbance levels and are generally typified as either urban, suburban or rural areas. These land use types may be ecologically studied along an urbanization gradient, with the intention of obtaining meaningful comparisons. An urbanization gradient contains an urban landscape which consists of a densely built and developed core surrounded by an area of decreasing development and increasing 'naturalness'. The use of urbanization gradients has been proven world-wide as a useful tool for the study of changes in ecological patterns and processes across landscapes. This approach has been used to examine many different impacts of urbanization, namely on invertebrate communities, bird community composition and plant community composition. Using biological indicators to determine the degree of anthropogenic impact on the environment has proven effective in past studies. These indicators can be used to monitor ecological change following habitat disturbance, identify changing trends over time, provide early warning systems of degradation and diagnose the cause of existing problems. Several authors have supported the use of arthropods as suitable indicators of disturbance. The aim of this study was to determine what impact disturbance, due to urbanization, may have had on the diversity and abundances of epigeal (surface roaming) arthropods (focussing on ants, beetles and spiders) following an urbanization gradient approach. In addition, plant and soil data were combined with the arthropod analysis for each site studied, in order to obtain a better picture of how arthropod community composition would change in relation to these factors. The ant group were the numerically dominant group of the arthropods studied, although the beetles did have the highest number of species captured. Spiders were caught in low abundances, but were also represented by a high number of species. Dramatic decreasing trends were observed with respect to the ant abundances and diversity from rural to the more urbanized sites. Quite the opposite, seemed to occur with the beetles and spiders, who were dominant in species and numbers in the urbanized areas. This trend may be explained on account of the occurrence of generalists and opportunistic beetle and spider species, which seem to thrive in these heterogenous urban habitats. When considering environmental components, percentage bare-ground and sand concentration seemed to be the determining factors in the rural sites, around which the ant group aggregated. Sandy habitats with patches of bare-ground provide more favourable micro-habitats for the ant species to roam and scavenge in, and are advantageous for nest building. Clay concentration and abundance of fruit seemed to assist in providing favourable habitats for the opportunistic and generalist beetle species, in the urbanized areas. High clay concentrations in the urban areas provided ideal conditions for abundant organic covering which would favour saprophagous (feed on decaying organic matter) beetle species and support diverse prey for the predatory beetle and spider species to feed on. Abundance of fruit may have attracted numerous herbivorous beetles (frugivorous beetles). Urbanization seemed to have a more pronounced effect on ant diversity and abundances in comparison to the beetles and spiders, and therefore recommended for future utilization as a suitable "Bio-indicator" group for further local disturbance studies. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Vertebrates, annelids, and arthropods have evolved to form their body plans via segmentation. The question is whether this process stems from a common, segmented ancestor or if segmentation in these three phyla evolved from a series of independent events. To determine which of these theories is true, we look to determining whether these phyla share any pathways in the development of their segments. The Notch signaling pathway is a well-known pathway that vertebrates utilize for segmentation. Without it, somitogenesis does not occur properly as the segmentation oscillator is not functioning. Drosophila does not use this pathway for segmentation, but several other arthropods have recently been found to utilize it in the formation and maintenance of their segments (17-24). There has been debate as to whether Tribolium castaneum also uses the Notch pathway during segmentation as previous knockdowns of the Notch and Delta genes have led to a loss of segments and appendages/mouthparts (25-27). To determine this pathway’s involvement in Tribolium segmentation, I knocked down the Delta gene via eRNAi and attempted to determine Notch and Delta expression patterns via in situ hybridization. My results were inconclusive for determining the role of the Notch signaling pathway in segmentation. In the Delta dsRNA embryos, a loss of the labial segment, head and mouthpart defects, a loss of leg formation, and midline defects were seen. Future experiments need to be performed to determine whether an overexpression of mesoderm, ectoderm, or both is the cause of the defective ventral midline and whether this could lead to a loss of segments later in development. Overall, I can conclude that the Notch signaling pathway plays a role in mouthpart/leg development, the labial segment, and what I believe to be lateral inhibition between mesoderm and ectoderm determination.

This study was carried out in a woodland on the campus of University of Western Sydney at Richmond, Australia to investigate seasonal effects and recovery speed of arboreal arthropods after disturbance. Twenty one pairs of Melaleuca linariifolia Sm. trees were sampled using insecticide spraying in a log2 nine period sequence (1-32) of weeks supplemented by additional samples to incorporate seasonal (weeks 24 and 48) and annual (week 52) samples. Using species accumulation curves, it was found that four collectors provided a reasonable representation of a tree's fauna and that a single tree does not provide a representative sample of the arthropod fauna found on trees of this species in the study area. The application of richness and evenness indices in different seasons showed significant changes in diversity. It was clear from the findings of the study that careful attention needs to be paid to experimental design. Under replication is the normal situation in previous studies and the effects of location, season and disturbance are all critical factors affecting the estimation of diversity. / Doctor of Philosophy (PhD)

Human activities have dramatically altered the functioning of ecosystems through the ages. Urbanization illustrates the effect of anthropogenic activity by the transformation of natural areas to ecologically disturbed regions (development of towns, cities and settlements). The growing need for urban employment in South Africa has led to an increase in the number of informal settlements on the periphery of urban areas. These settlements result in fragmentation and sprawling of cities, which intensifies strain on the natural environment. Fragmentation in urban regions then leads to the formation of 'patches' of land which exhibit different disturbance levels and are generally typified as either urban, suburban or rural areas. These land use types may be ecologically studied along an urbanization gradient, with the intention of obtaining meaningful comparisons. An urbanization gradient contains an urban landscape which consists of a densely built and developed core surrounded by an area of decreasing development and increasing 'naturalness'. The use of urbanization gradients has been proven world-wide as a useful tool for the study of changes in ecological patterns and processes across landscapes. This approach has been used to examine many different impacts of urbanization, namely on invertebrate communities, bird community composition and plant community composition. Using biological indicators to determine the degree of anthropogenic impact on the environment has proven effective in past studies. These indicators can be used to monitor ecological change following habitat disturbance, identify changing trends over time, provide early warning systems of degradation and diagnose the cause of existing problems. Several authors have supported the use of arthropods as suitable indicators of disturbance. The aim of this study was to determine what impact disturbance, due to urbanization, may have had on the diversity and abundances of epigeal (surface roaming) arthropods (focussing on ants, beetles and spiders) following an urbanization gradient approach. In addition, plant and soil data were combined with the arthropod analysis for each site studied, in order to obtain a better picture of how arthropod community composition would change in relation to these factors. The ant group were the numerically dominant group of the arthropods studied, although the beetles did have the highest number of species captured. Spiders were caught in low abundances, but were also represented by a high number of species. Dramatic decreasing trends were observed with respect to the ant abundances and diversity from rural to the more urbanized sites. Quite the opposite, seemed to occur with the beetles and spiders, who were dominant in species and numbers in the urbanized areas. This trend may be explained on account of the occurrence of generalists and opportunistic beetle and spider species, which seem to thrive in these heterogenous urban habitats. When considering environmental components, percentage bare-ground and sand concentration seemed to be the determining factors in the rural sites, around which the ant group aggregated. Sandy habitats with patches of bare-ground provide more favourable micro-habitats for the ant species to roam and scavenge in, and are advantageous for nest building. Clay concentration and abundance of fruit seemed to assist in providing favourable habitats for the opportunistic and generalist beetle species, in the urbanized areas. High clay concentrations in the urban areas provided ideal conditions for abundant organic covering which would favour saprophagous (feed on decaying organic matter) beetle species and support diverse prey for the predatory beetle and spider species to feed on. Abundance of fruit may have attracted numerous herbivorous beetles (frugivorous beetles). Urbanization seemed to have a more pronounced effect on ant diversity and abundances in comparison to the beetles and spiders, and therefore recommended for future utilization as a suitable "Bio-indicator" group for further local disturbance studies. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.