Matching Items (1,614)
Filtering by
- Creators: School of Life Sciences
Description
Of all the signals and cues that orchestrate the activities of a social insect colony, the reproductives' fertility pheromones are perhaps the most fundamental. These pheromones regulate reproductive division of labor, a defining characteristic of eusociality. Despite their critical role, reproductive fertility pheromones are not evenly expressed across the development of a social insect colony and may even be absent in the earliest colony stages. In the ant Camponotus floridanus, queens of incipient colonies do not produce the cuticular hydrocarbons that serve as fertility and egg-marking signals in this species. My dissertation investigates the consequences of the dramatic change in the quantity of these pheromones that occurs as the colony grows. C. floridanus workers from large, established colonies use egg surface hydrocarbons to discriminate among eggs. Eggs with surface hydrocarbons typical of eggs laid by established queens are nurtured, whereas eggs lacking these signals (i.e., eggs laid by workers and incipient queens) are destroyed. I characterized how workers from incipient colonies responded to eggs lacking queen fertility hydrocarbons. I found that established-queen-laid eggs, incipient-queen-laid eggs, and worker-laid eggs were not destroyed by workers at this colony stage. Destruction of worker-laid eggs is a form of policing, and theoretical models predict that policing should be strongest in incipient colonies. Since there was no evidence of policing by egg-eating in incipient C. floridanus colonies, I searched for evidence of another policing mechanism at this colony stage. Finding none, I discuss reasons why policing behavior may not be expressed in incipient colonies. I then considered the mechanism that accounts for the change in workers' response to eggs. By manipulating ants' egg experience and testing their egg-policing decisions, I found that ants use a combination of learned and innate criteria to discriminate between targets of care and destruction. Finally, I investigated how the increasing strength of queen-fertility hydrocarbons affects nestmate recognition, which also relies on cuticular hydrocarbons. I found that queens with strong fertility hydrocarbons can be transferred between established colonies without aggression, but they cannot be introduced into incipient colonies. Queens from incipient colonies cannot be transferred into incipient or established colonies.
ContributorsMoore, Dani (Author) / Liebig, Juergen (Thesis advisor) / Gadau, Juergen (Committee member) / Pratt, Stephen (Committee member) / Smith, Brian (Committee member) / Rutowski, Ronald (Committee member) / Arizona State University (Publisher)
Created2012
Description
The coordination of group behavior in the social insects is representative of a broader phenomenon in nature, emergent biological complexity. In such systems, it is believed that large-scale patterns result from the interaction of relatively simple subunits. This dissertation involved the study of one such system: the social foraging of the ant Temnothorax rugatulus. Physically tiny with small population sizes, these cavity-dwelling ants provide a good model system to explore the mechanisms and ultimate origins of collective behavior in insect societies. My studies showed that colonies robustly exploit sugar water. Given a choice between feeders unequal in quality, colonies allocate more foragers to the better feeder. If the feeders change in quality, colonies are able to reallocate their foragers to the new location of the better feeder. These qualities of flexibility and allocation could be explained by the nature of positive feedback (tandem run recruitment) that these ants use. By observing foraging colonies with paint-marked ants, I was able to determine the `rules' that individuals follow: foragers recruit more and give up less when they find a better food source. By altering the nutritional condition of colonies, I found that these rules are flexible - attuned to the colony state. In starved colonies, individual ants are more likely to explore and recruit to food sources than in well-fed colonies. Similar to honeybees, Temmnothorax foragers appear to modulate their exploitation and recruitment behavior in response to environmental and social cues. Finally, I explored the influence of ecology (resource distribution) on the foraging success of colonies. Larger colonies showed increased consistency and a greater rate of harvest than smaller colonies, but this advantage was mediated by the distribution of resources. While patchy or rare food sources exaggerated the relative success of large colonies, regularly (or easily found) distributions leveled the playing field for smaller colonies. Social foraging in ant societies can best be understood when we view the colony as a single organism and the phenotype - group size, communication, and individual behavior - as integrated components of a homeostatic unit.
ContributorsShaffer, Zachary (Author) / Pratt, Stephen C (Thesis advisor) / Hölldobler, Bert (Committee member) / Janssen, Marco (Committee member) / Fewell, Jennifer (Committee member) / Liebig, Juergen (Committee member) / Arizona State University (Publisher)
Created2014
Description
Warning coloration deters predators from attacking prey that are defended, usually by being distasteful, toxic, or otherwise costly for predators to pursue and consume. Predators may have an innate response to warning colors or learn to associate them with a defense through trial and error. In general, predators should select for warning signals that are easy to learn and recognize. Previous research demonstrates long-wavelength colors (e.g. red and yellow) are effective because they are readily detected and learned. However, a number of defended animals display short-wavelength coloration (e.g. blue and violet), such as the pipevine swallowtail butterfly (Battus philenor). The role of blue coloration in warning signals had not previously been explicitly tested. My research showed in laboratory experiments that curve-billed thrashers (Toxostoma curvirostre) and Gambel's quail (Callipepla gambelii) can learn and recognize the iridescent blue of B. philenor as a warning signal and that it is innately avoided. I tested the attack rates of these colors in the field and blue was not as effective as orange. I concluded that blue colors may function as warning signals, but the effectiveness is likely dependent on the context and predator.
Blue colors are often iridescent in nature and the effect of iridescence on warning signal function was unknown. I reared B. philenor larvae under varied food deprivation treatments. Iridescent colors did not have more variation than pigment-based colors under these conditions; variation which could affect predator learning. Learning could also be affected by changes in appearance, as iridescent colors change in both hue and brightness as the angle of illuminating light and viewer change in relation to the color surface. Iridescent colors can also be much brighter than pigment-based colors and iridescent animals can statically display different hues. I tested these potential effects on warning signal learning by domestic chickens (Gallus gallus domesticus) and found that variation due to the directionality of iridescence and a brighter warning signal did not influence learning. However, blue-violet was learned more readily than blue-green. These experiments revealed that the directionality of iridescent coloration does not likely negatively affect its potential effectiveness as a warning signal.
Blue colors are often iridescent in nature and the effect of iridescence on warning signal function was unknown. I reared B. philenor larvae under varied food deprivation treatments. Iridescent colors did not have more variation than pigment-based colors under these conditions; variation which could affect predator learning. Learning could also be affected by changes in appearance, as iridescent colors change in both hue and brightness as the angle of illuminating light and viewer change in relation to the color surface. Iridescent colors can also be much brighter than pigment-based colors and iridescent animals can statically display different hues. I tested these potential effects on warning signal learning by domestic chickens (Gallus gallus domesticus) and found that variation due to the directionality of iridescence and a brighter warning signal did not influence learning. However, blue-violet was learned more readily than blue-green. These experiments revealed that the directionality of iridescent coloration does not likely negatively affect its potential effectiveness as a warning signal.
ContributorsPegram, Kimberly Vann (Author) / Rutowski, Ronald L (Thesis advisor) / Hoelldobler, Berthold (Committee member) / Liebig, Juergen (Committee member) / McGraw, Kevin (Committee member) / Smith, Brian H. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Like individual organisms, complex social groups are able to maintain predictable trajectories of growth, from initial colony foundation to mature reproductively capable units. They do so while simultaneously responding flexibly to variation in nutrient availability and intake. Leafcutter ant colonies function as tri-trophic systems, in which the ants harvest vegetation to grow a fungus that, in turn, serves as food for the colony. Fungal growth rates and colony worker production are interdependent, regulated by nutritional and behavioral feedbacks. Fungal growth and quality are directly affected by worker foraging decisions, while worker production is, in turn, dependent on the amount and condition of the fungus. In this dissertation, I first characterized the growth relationship between the workers and the fungus of the desert leafcutter ant Acromyrmex versicolor during early stages of colony development, from colony foundation by groups of queens through the beginnings of exponential growth. I found that this relationship undergoes a period of slow growth and instability when workers first emerge, and then becomes allometrically positive. I then evaluated how mass and element ratios of resources collected by the ants are translated into fungus and worker population growth, and refuse, finding that colony digestive efficiency is comparable to digestive efficiencies of other herbivorous insects and ruminants. To test how colonies behaviorally respond to perturbations of the fungus garden, I quantified activity levels and task performance of workers in colonies with either supplemented or diminished fungus gardens, and found that colonies adjusted activity and task allocation in response to the fungus garden size. Finally, to identify possible forms of nutrient limitation, I measured how colony performance was affected by changes in the relative amounts of carbohydrates, protein, and phosphorus available in the resources used to grow the fungus garden. From this experiment, I concluded that colony growth is primarily carbohydrate-limited.
ContributorsClark, Rebecca, 1981- (Author) / Fewell, Jennifer H (Thesis advisor) / Mueller, Ulrich (Committee member) / Liebig, Juergen (Committee member) / Elser, James (Committee member) / Harrison, Jon (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation consists of two essays. The first measures the degree to which schooling accounts for differences in industry value added per worker. Using a sample of 107 economies and seven industries, the paper considers the patterns in the education levels of various industries and their relative value added per worker. Agriculture has notably less schooling and is less productive than other sectors, while a group of services including financial services, education and health care has higher rates of schooling and higher value added per worker. The essay finds that in the case of these specific industries education is important in explaining sector differences, and the role of education all other industries are less defined. The second essay provides theory to investigate the relationship between agriculture and schooling. During structural transformation, workers shift from the agriculture sector with relatively low schooling to other sectors which have more schooling. This essay explores to what extent changes in the costs of acquiring schooling drive structural transformation using a multi-sector growth model which includes a schooling choice. The model is disciplined using cross country data on sector of employment and schooling constructed from the IPUM International census collection. Counterfactual exercises are used to determine how much structural transformation is accounted for by changes in the cost of acquiring schooling. These changes account for small shares of structural transformation in all economies with a median near zero.
ContributorsSchreck, Paul (Author) / Herrendorf, Berthold (Committee member) / Lagakos, David (Committee member) / Schoellman, Todd (Committee member) / Arizona State University (Publisher)
Created2011
Description
A notable feature of advanced eusocial insect groups is a division of labor within the sterile worker caste. However, the physiological aspects underlying the differentiation of behavioral phenotypes are poorly understood in one of the most successful social taxa, the ants. By starting to understand the foundations on which social behaviors are built, it also becomes possible to better evaluate hypothetical explanations regarding the mechanisms behind the evolution of insect eusociality, such as the argument that the reproductive regulatory infrastructure of solitary ancestors was co-opted and modified to produce distinct castes. This dissertation provides new information regarding the internal factors that could underlie the division of labor observed in both founding queens and workers of Pogonomyrmex californicus ants, and shows that changes in task performance are correlated with differences in reproductive physiology in both castes. In queens and workers, foraging behavior is linked to elevated levels of the reproductively-associated juvenile hormone (JH), and, in workers, this behavioral change is accompanied by depressed levels of ecdysteroid hormones. In both castes, the transition to foraging is also associated with reduced ovarian activity. Further investigation shows that queens remain behaviorally plastic, even after worker emergence, but the association between JH and behavioral bias remains the same, suggesting that this hormone is an important component of behavioral development in these ants. In addition to these reproductive factors, treatment with an inhibitor of the nutrient-sensing pathway Target of Rapamycin (TOR) also causes queens to become biased towards foraging, suggesting an additional sensory component that could play an important role in division of labor. Overall, this work provides novel identification of the possible regulators behind ant division of labor, and suggests how reproductive physiology could play an important role in the evolution and regulation of non-reproductive social behaviors.
ContributorsDolezal, Adam G (Author) / Amdam, Gro V (Thesis advisor) / Brent, Colin S. (Committee member) / Gadau, Juergen (Committee member) / Hoelldobler, Bert (Committee member) / Liebig, Juergen (Committee member) / Arizona State University (Publisher)
Created2012
Description
The repression of reproductive competition and the enforcement of altruism are key components to the success of animal societies. Eusocial insects are defined by having a reproductive division of labor, in which reproduction is relegated to one or few individuals while the rest of the group members maintain the colony and help raise offspring. However, workers have retained the ability to reproduce in most insect societies. In the social Hymenoptera, due to haplodiploidy, workers can lay unfertilized male destined eggs without mating. Potential conflict between workers and queens can arise over male production, and policing behaviors performed by nestmate workers and queens are a means of repressing worker reproduction. This work describes the means and results of the regulation of worker reproduction in the ant species Aphaenogaster cockerelli. Through manipulative laboratory studies on mature colonies, the lack of egg policing and the presence of physical policing by both workers and queens of this species are described. Through chemical analysis and artificial chemical treatments, the role of cuticular hydrocarbons as indicators of fertility status and the informational basis of policing in this species is demonstrated. An additional queen-specific chemical signal in the Dufour's gland is discovered to be used to direct nestmate aggression towards reproductive competitors. Finally, the level of actual worker-derived males in field colonies is measured. Together, these studies demonstrate the effectiveness of policing behaviors on the suppression of worker reproduction in a social insect species, and provide an example of how punishment and the threat of punishment is a powerful force in maintaining cooperative societies.
ContributorsSmith, Adrian A. (Author) / Liebig, Juergen (Thesis advisor) / Hoelldobler, Bert (Thesis advisor) / Gadau, Juergen (Committee member) / Johnson, Robert A. (Committee member) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation is a collection of two essays relating to the dynamic effects of taxation.
In the first chapter, I focus on a key challenge faced by tax reforms: their short-run
welfare consequences. I examine a consumption-based tax reform that, despite the long-run welfare gains it generates, causes the welfare for some groups such as retirees or the working poor to fall during transition between steady states. Using a life-cycle model with heterogeneous households, I show how to devise a transition path from the current U.S. federal tax system to a consumption-based tax system that improves the welfare of current generations as well as those who are born in the long-run steady state. In a nutshell, all households alive at the time of the policy change can choose when they want to switch to the new tax system, or whether they want to switch at all. I find that implementing a tax reform with this feature improves the welfare of 95% of the population in the short run, compared to less than 25% of population in the conventional case with no choice. It takes about 20 years for half of the population to pay their taxes under the new tax code.
In the second chapter, I study the aggregate consequences of the differential tax treatments of U.S. businesses focusing on the role of legal forms of organization. I develop an industry equilibrium model in which the organizational form is an endogenous choice.
This model incorporates the key trade-off that businesses face when choosing their legal forms: the tax treatment of the business income; the access to external capital, and the potential level and evolution of productivity over time.
The model is matched to the firm dynamic features of U.S. businesses and the contributing share of each legal form in total output. Using the model, I study revenue-neutral tax reforms in which legal forms receive the same tax treatments, and
I find that the incentives induced by tax structure for organizational form and external finance are both large. Relative to the benchmark economy, unifying the tax code for all legal forms, can lead to 8% increase in the aggregate output.
In the first chapter, I focus on a key challenge faced by tax reforms: their short-run
welfare consequences. I examine a consumption-based tax reform that, despite the long-run welfare gains it generates, causes the welfare for some groups such as retirees or the working poor to fall during transition between steady states. Using a life-cycle model with heterogeneous households, I show how to devise a transition path from the current U.S. federal tax system to a consumption-based tax system that improves the welfare of current generations as well as those who are born in the long-run steady state. In a nutshell, all households alive at the time of the policy change can choose when they want to switch to the new tax system, or whether they want to switch at all. I find that implementing a tax reform with this feature improves the welfare of 95% of the population in the short run, compared to less than 25% of population in the conventional case with no choice. It takes about 20 years for half of the population to pay their taxes under the new tax code.
In the second chapter, I study the aggregate consequences of the differential tax treatments of U.S. businesses focusing on the role of legal forms of organization. I develop an industry equilibrium model in which the organizational form is an endogenous choice.
This model incorporates the key trade-off that businesses face when choosing their legal forms: the tax treatment of the business income; the access to external capital, and the potential level and evolution of productivity over time.
The model is matched to the firm dynamic features of U.S. businesses and the contributing share of each legal form in total output. Using the model, I study revenue-neutral tax reforms in which legal forms receive the same tax treatments, and
I find that the incentives induced by tax structure for organizational form and external finance are both large. Relative to the benchmark economy, unifying the tax code for all legal forms, can lead to 8% increase in the aggregate output.
ContributorsRaei, Sepideh (Author) / Ventura, Gustavo (Thesis advisor) / Herrendorf, Berthold (Committee member) / Bick, Alexander (Committee member) / Arizona State University (Publisher)
Created2018
Description
This dissertation consists of two essays with a macroeconomic approach to economic development. These essays explore specific barriers that prevent economic agents from exploiting opportunities across regions or sectors in developing countries, and to what extent the observed allocations are inefficient outcomes or just an efficient response to economic fundamentals and technological constraints.
The first chapter is motivated by the fact that a prominent feature of cities in developing countries is the existence of slums: locations with low housing-quality and informal property rights. This paper focuses on the allocation of land across slums and formal housing, and emphasizes the role of living in central urban areas for the formation of slums. I build a quantitative spatial general equilibrium model to study the aggregate effects of anti-slum policies and use microdata from India for the quantitative implementation. According to my findings, demolishing slums in central urban areas leads to a decrease in welfare, aggregate labor productivity, and urban population. In contrast, decreasing formal housing distortions in India to the U.S. level increases the urban population share by 20% and labor productivity by 2.4%, and reduces the share of the urban population living in slums by 19%.
The second chapter is motivated by the fact that labor productivity gaps between rich and poor countries are much larger for agriculture than for non-agriculture. Using detailed data from Mexican farms, this paper shows that value added per worker is frequently over two times larger in cash crops than in staple crops, yet most farmers choose to produce staples. These findings imply that the agricultural productivity gap is actually a staple productivity gap and understanding production decisions of farmers is crucial to explain why labor productivity is so low in poor countries. This paper develops a general equilibrium framework in which subsistence consumption and interregional trade costs determine the efficient selection of farmers into types of crops. The quantitative results of the model imply that decreasing trade costs in Mexico to the U.S. level reduces the ratio of employment in staple to cash crops by 17% and increases agricultural labor productivity by 14%.
The first chapter is motivated by the fact that a prominent feature of cities in developing countries is the existence of slums: locations with low housing-quality and informal property rights. This paper focuses on the allocation of land across slums and formal housing, and emphasizes the role of living in central urban areas for the formation of slums. I build a quantitative spatial general equilibrium model to study the aggregate effects of anti-slum policies and use microdata from India for the quantitative implementation. According to my findings, demolishing slums in central urban areas leads to a decrease in welfare, aggregate labor productivity, and urban population. In contrast, decreasing formal housing distortions in India to the U.S. level increases the urban population share by 20% and labor productivity by 2.4%, and reduces the share of the urban population living in slums by 19%.
The second chapter is motivated by the fact that labor productivity gaps between rich and poor countries are much larger for agriculture than for non-agriculture. Using detailed data from Mexican farms, this paper shows that value added per worker is frequently over two times larger in cash crops than in staple crops, yet most farmers choose to produce staples. These findings imply that the agricultural productivity gap is actually a staple productivity gap and understanding production decisions of farmers is crucial to explain why labor productivity is so low in poor countries. This paper develops a general equilibrium framework in which subsistence consumption and interregional trade costs determine the efficient selection of farmers into types of crops. The quantitative results of the model imply that decreasing trade costs in Mexico to the U.S. level reduces the ratio of employment in staple to cash crops by 17% and increases agricultural labor productivity by 14%.
ContributorsRivera Padilla, Alberto (Author) / Schoellman, Todd K. (Thesis advisor) / Herrendorf, Berthold (Thesis advisor) / Ferraro, Domenico (Committee member) / Arizona State University (Publisher)
Created2019
Description
The inherent risk in testing drugs has been hotly debated since the government first started regulating the drug industry in the early 1900s. Who can assume the risks associated with trying new pharmaceuticals is unclear when looked at through society's lens. In the mid twentieth century, the US Food and Drug Administration (FDA) published several guidance documents encouraging researchers to exclude women from early clinical drug research. The motivation to publish those documents and the subsequent guidance documents in which the FDA and other regulatory offices established their standpoints on women in drug research may have been connected to current events at the time. The problem of whether women should be involved in drug research is a question of who can assume risk and who is responsible for disseminating what specific kinds of information. The problem tends to be framed as one that juxtaposes the health of women and fetuses and sets their health as in opposition. That opposition, coupled with the inherent uncertainty in testing drugs, provides for a complex set of issues surrounding consent and access to information.
ContributorsMeek, Caroline Jane (Author) / Maienschein, Jane (Thesis director) / Brian, Jennifer (Committee member) / School of Life Sciences (Contributor) / Sanford School of Social and Family Dynamics (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05