A lengthy, and at times heated, debate on the regulation of animal numbers has proceeded in the literature for over half a century. A wide variety of causal agents - from sun spots to a shortage of trace elements - has been proposed to explain the observed densities, and a wide variety of mechanisms has also been proposed - from natural selection to chance. Only occasionally have any of these proposals been rigorously tested, and the survival of partially or totally conflicting hypotheses has been correspondingly high. I have attempted to test just one of these proposals: the polymorphism hypothesis of Chitty (Proc. Ecol. Soc. Australia 2:51-78, 1967.) According to this hypothesis, any natural population which lives in a highly favourable habitat can regulate its numbers through the action of two morphs, one characterized by a high fecundity and the other by a superior ability to hold its position in the environment. Population density is postulated to be a function of the relative frequency of the morphs and to change in a predictable way. I have conducted five experiments to investigate the existence of, and the mode of interaction between, these presumed morphs in Tribolium confusum, the questions asked being: 1) Is the density achieved by open populations (i.e. those from which emigration is allowed) different from that in closed populations (i.e. those from which emigration is prevented)? 2) Is the mechanism of regulation in open populations different from that in closed populations? 3) Is the tendency to migrate a constant property of individuals? 4) Is the density achieved by populations founded by migrants different from that of populations founded by non-migrants? 5) Is the density achieved by open populations (with migration by self-selection) different from that achieved by closed populations from which an equal number of animals are removed at random? I found the answers to all these questions to be 'yes', and the differences in each case to be in the direction predicted by the polymorphism hypothesis. I suggest that the polymorphism hypothesis is useful for predicting future densities of populations from which emigration is occurring, but is not useful for predicting densities in populations 1) from which animals cannot escape or 2) in which mortality caused by extrinsic factors is so great that, despite high fecundity, the populations are unable to produce a migrating surplus. I argue that 1) and 2) are rare in nature, or at least have been studied rather seldom. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1947. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 54-68).

Master of Science / Department of Grain Science and Industry / Subramanyam Bhadriraju / Heat treatment involves raising the ambient temperature of food-processing facilities such as flour mills to 50-60oC for killing stored-product insects. However, very little is known about the influence of sanitation on responses of stored-product insects to structural heat treatments. The impact of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum, an economically important pest in flour mills, were investigated during three 24 h structural heat treatments of the Kansas State University pilot flour mill. Two sanitation levels, dusting of wheat flour (~0.5 g) and 2-cm deep flour (~43 g), were created in 25 plastic bioassay boxes each holding 50 eggs, 50 young larvae, 50 old larvae, 50 pupae, and 50 adults of T. castaneum in separate compartments. Five boxes were placed on each of five floors of the pilot mill during 13-14 May 2009, 25-26 August 2009, and 7-8 May 2010 heat treatments using forced air gas heaters. During the August 2009 and May 2010 heat treatments, 100 eggs or 100 adults of T. castaneum were exposed inside each 20 cm diameter by 15 cm high PVC ring placed only on first and third floors and holding 0.1 (15 g), 0.2 (38 g), 1 (109 g), 3 (388 g), 6 (937 g), or 10 (1645 g) cm deep wheat flour. Among the mill floors, first floor had lower maximum temperature. The first floor rests on a thick concrete foundation, did not get heated from both sides unlike other floors, and had poor air movement resulting in cold pockets (temperatures <50oC). Mortality of life stages was lower on first floor than other floors and adults were less susceptible than other life stages especially on first floor. In general, both these tests have shown that the mortality of T. castaneum life stages were influenced by how quickly temperatures reached 50oC, how long temperatures were held above 50oC, and the maximum temperature. Protective effects of sanitation were evident only if temperatures did not reach 50oC. However, removal of flour accumulations is essential to improve heat treatment effectiveness against all T. castaneum life stages during a 24 h treatment.

Master of Science / Department of Grain Science and Industry / Subramanyam Bhadriraju / During heat treatment, the ambient temperature of grain-processing facilities is raised to 50-60°C for at least 24 hours to manage stored-product insects. Young larvae (first instars) of the red flour beetle, Tribolium castaneum (Herbst), are the most heat tolerant stage at 50-60°C. A thermal death kinetic (TDK) model predicted survival of T. castaneum young larvae exposed to six constant elevated temperatures between 42 and 60ºC. The model is based on logarithmic survival of T. castaneum as a function of time and logarithmic reduction in larval survival as a function of temperature. The model was validated with 12 independent temperature datasets collected during heat treatments of pilot-scale and commercial grain-processing facilities. Young larval survival in plastic boxes/vials with flour was used to validate model predictions. The heating rate to 50°C from the ambient among the 12 datasets ranged from 0.9-7.8°C/h. Mean absolute deviations between observed and predicted larval survival for 10 of the 12 datasets ranged from 2.1-11.4%; it was 16.2 and 18.3% for two other datasets. The TDK model can be used to predict survival of young larvae of T. castaneum based on time-dependent temperature profile obtained at any given location during heat treatment of grain-processing facilities. In three commercial grain-processing facilities heat treatments were conducted for 24-27.7 hours using forced-air gas heaters. Temperatures attained and survival of 20 eggs, 20 young larvae, and 20 adults of T. castaneum in bioassay vials at various locations were determined. Across all three facilities, 5 out of 2720 adults in 136 vials, 1 out of 960 young larvae in 48 vials, and 0 out of 1760 eggs in 88 vials were alive at the end of the heat treatment. In each facility, the time in hours for 1% predicted survival of T. castaneum young larvae was positively related to how quickly temperatures reached 50°C, and negatively related to rate of heating to 50°C from the ambient, time above 50°C in hours, and the maximum temperature. Bioassays with T. castaneum life stages and the TDK model can be used to gauge effectiveness of facility heat treatments.

Intraspecific genetic diversity is an important attribute of natural populations and is deemed critical for their adaptive potential and persistence. However, we have limited empirical understanding of the impact of genetic diversity on population performance under different conditions. For my dissertation, I conducted long-term laboratory experiments with populations of the flour beetle Tribolium castaneum to test the consequences of genetic variation for population dynamic stability and niche evolution. In Chapter 1, I show that genetic variation prevented population extinction in a novel habitat. In addition, genetically diverse populations were more stable, both in a novel heterogeneous habitat and in their ancestral habitat. In the ancestral habitat, alleles from a single founding lineage dominated the dynamics, leading to increased stability of genetically diverse populations. However, such as selective effect was not observed in the novel heterogeneous habitat. Therefore, while genetic variation within populations increased their stability and persistence, the magnitude of the impact and its mechanism depended on the selective habitat. In Chapter 2, I ask whether genetic variation also facilitates resource niche expansion, i.e., use of a novel resource. Using stable carbon isotopes, I analyzed diets of beetles sampled from the above experiment and quantified the rate of change in resource use. Contrary to theoretical predictions, I found that genetic variation for resource use had no effect on the rate of niche evolution. Furthermore, behavioral niche expansion accounted for most of the adaptation to the novel resource, and the behavioral change hindered subsequent evolutionary change in resource use. It is thus apparent that in the short term, behavioral plasticity in niche use may impose far greater constraints on niche evolution than the amount of standing genetic variation. Mathematical models predict that intraspecific competition generates selection for niche evolution, and that genetic variation increases the response to selection. Therefore, I hypothesized that the impact of genetic variation on resource niche evolution may depend on the degree of intraspecific competition. In the final chapter of this thesis, I describe results of an experiment to test this hypothesis. I found that genetic variation and competition indeed interacted to increase the rate of niche expansion in T. castaneum, but that their impacts were temporally variable. Furthermore, the two factors acted on different components of niche evolution: while competition only affected the degree of niche expansion, genetic variation also promoted maintenance of individual variation in resource use. In summary, my thesis describes experiments to test for the ecological and evolutionary impacts of intraspecific genetic variation; and its interaction with behavioral plasticity, intraspecific competition, and resource availability. Genetic diversity and behavioral plasticity are common features of living organisms, and therefore it is vital to understand their combined consequences for population ecological and evolutionary dynamics. In addition, natural populations often face intense competition for limited resources. Hence the experimental results presented here can help us to better understand how populations overcome these resource constraints, given their specific genetic composition. Biologists are increasingly aware that the intricate connection between ecological and evolutionary dynamics is important to gain a more complete understanding of population biology. The work described here represents one of the few experiments providing such detailed mechanistic understanding of the interactions between- and consequences of - key ecological and evolutionary parameters. Finally, the results have important implications for conservation biology, because they show that the effects of genetic diversity can vary greatly depending on a number of population and environmental parameters. / text

No abstract.

Density dependence is a common phenomenon in nature, and the intensity of density dependence is driven by competition over depletable resources. Habitat selection patterns are often density-dependent, and are driven by decreasing population mean fitness in a habitat as population density increases in that habitat. Yet not all resources are depletable, and non-depletable resources may sometimes be most important in dictating patterns of habitat selection. Ectotherms, for example, are defined by their dependence on environmental temperature to regulate body temperature, and temperature is often the most important resource for ectotherms. Is density dependence an important mechanism in ectotherms, especially when temperature is a limiting factor? In this thesis, I examine density dependence of fitness and habitat selection by ectotherms using red flour beetles and common gartersnakes. In chapter one and three, I test whether density-dependent habitat selection occurs when habitats differ in both temperature and food availability with red flour beetles and common gartersnakes, respectively. In chapter two, I modify the isodar model of habitat selection to account for the effect of temperature on ectotherms, derive predictions from the modified model, and test these predictions with controlled experiments with red flour beetles selecting between habitats that differ in food quantity and temperature. Finally, in chapter four, I examine the effect of density on metrics of fitness and habitat selection with common gartersnakes. Red flour beetles exhibited strong density dependence in both habitat selection and fitness at their optimal temperature, but density dependence weakened at lower temperatures. Common gartersnakes exhibited mostly density-independent habitat selection with a strong preference for warm field habitat over cool forest habitat, but exhibited some density dependence in habitat selection within field habitat. Overall, my thesis demonstrates that ectotherms have variable density-dependent responses, and that these responses are strongly modulated by temperature.

Call number: LD2668 .T4 1985 S245 / Master of Science

Doctor of Philosophy / Department of Biology / Susan J. Brown / RNA interference (RNAi) is a natural gene-silencing phenomenon triggered by dsRNA (dsRNA). While RNAi is an endogenous process that plays essential roles in regulating gene expression it can also be harnessed as a tool for the study of gene function. Introducing dsRNA that is homologous to target mRNA into a cell triggers the RNAi response causing the destruction of the homologous mRNA and a loss of function phenotype. In some organisms, such as the nematode Caenorhabditis elegans, once dsRNA is introduced into the body cavity, the RNAi effect is seen throughout the organism because the dsRNA is taken up by individual cells and is then spread from cell to cell. This process has been termed the systemic RNAi response. For other organisms, such as the fruit fly Drosophila melanogaster, introduction of dsRNA into the body cavity does not result in a systemic RNAi response. This may be due to the cell’s inability to take up dsRNA or spread that dsRNA from cell to cell. For other organisms, including mammals, introduction of dsRNA into the body cavity does not result in a systemic RNAi response because the immune response causes dsRNA destruction before it can be utilized in the RNAi pathway. For organisms that do not exhibit a systemic RNAi response, complex genetic methods are needed to introduce dsRNA into cells to induce the RNAi response. Therefore, one of the challenges in utilizing RNAi as a genetic tool is introducing the dsRNA into individual cells. In recent years, systemic RNAi responses have been documented in both model and non-model organisms, making RNAi an accessible genetic tool. The red flour beetle, Tribolium castaneum is an emerging model organism that has a robust systemic RNAi response. However, the mechanism of systemic RNAi and the specific parameters required to obtain a strong systemic RNAi response in this organism have not been thoroughly investigated. The aim of this work is to provide data that can allow RNAi to be better utilized as a genetic tool in Tribolium and to use this information as a basis for the use of RNAi in other insects in which it can be performed. Specifically we provide data on the essential parameters necessary to achieve an effective systemic response in Tribolium, we describe differences in the systemic RNAi response between Drosophila and Tribolium, we analyze the conservation and function of RNAi machinery genes in Tribolium and we provide information on the genes critical for a systemic RNAi response in Tribolium.