Matching Items (286)
Description
Human-induced rapid environmental change (HIREC) influences nearly all of Earth's ecosystems through processes such as urbanization. Previous studies have found that urbanization influences biodiversity patterns, often yielding an increase in the abundance of a few urban-adapted taxa at the expense of native species diversity. The western black widow spider, Latrodectus hesperus, is a medically-important pest species that often forms dense urban subpopulations (i.e., infestations) relative to the low-density subpopulations found throughout undisturbed, desert habitat. Here, I employ field and laboratory studies to examine the population ecology and stoichiometry of this urban pest to increase our understanding of the mechanisms underlying its success. The population ecology of ten black widow subpopulations spread across metropolitan Phoenix, AZ was examined during the peak breeding season (June-August). This study revealed that arthropod prey abundance, female mass and population density of females showed significant spatial variation across the ten subpopulations. Additionally, prey abundance and foraging success, measured as the number of carcasses found in webs, were a strong determinant of female mass and population density within each subpopulation. To test the mechanisms that drive black widow infestations, I used ecological stoichiometry to examine the nutrient (nitrogen and phosphorus) composition of spiders and arthropod prey from urban habitat, desert habitat and a laboratory diet regime. These studies revealed that (1) spiders are more nutrient rich than cricket prey in the field, (2) spider subpopulations exhibit significant spatial variation in their nitrogen composition, (3) nutrient composition of urban spider subpopulations does not differ significantly from Sonoran desert subpopulations, (4) laboratory-reared spiders fed a diet of only laboratory-reared crickets are more nitrogen and phosphorus limited than field-captured spiders, and (5) cannibalism by laboratory-reared spiders alleviated phosphorus limitation, but not nitrogen limitation, when compared to field-captured spiders. This work highlights the need to examine the population ecology of species relationships, such as predator-prey dynamics, to fully understand the fecundity and population growth of urban pest species. Moreover, the integration of population ecology and stoichiometry illustrates the need to address mechanisms like nutrient limitation that may explain why urban pest populations thrive and native species diversity suffers following HIREC.
ContributorsTrubl, Patricia (Author) / Johnson, James C. (Thesis advisor) / Rutowski, Ronald (Thesis advisor) / McGraw, Kevin (Committee member) / Arizona State University (Publisher)
Created2012
Description
Foraging has complex effects on whole-organism homeostasis, and there is considerable evidence that foraging behavior is influenced by both environmental factors (e.g., food availability, predation risk) and the physiological condition of an organism. The optimization of foraging behavior to balance costs and benefits is termed state-dependent foraging (SDF) while behavior that seeks to protect assets of fitness is termed the asset protection principle (APP). A majority of studies examining SDF have focused on the role that energy balance has on the foraging of organisms with high metabolism and high energy demands ("high-energy systems" such as endotherms). In contrast, limited work has examined whether species with low energy use ("low-energy systems" such as vertebrate ectotherms) use an SDF strategy. Additionally, there is a paucity of evidence demonstrating how physiological and environmental factors other than energy balance influence foraging behavior (e.g. hydration state and free-standing water availability). Given these gaps in our understanding of SDF behavior and the APP, I examined the state-dependency and consequences of foraging in a low-energy system occupying a resource-limited environment - the Gila monster (Heloderma suspectum, Cope 1869). In contrast to what has been observed in a wide variety of taxa, I found that Gila monsters do not use a SDF strategy to manage their energy reserves and that Gila monsters do not defend their energetic assets. However, hydration state and free-standing water availability do affect foraging behavior of Gila monsters. Additionally, as Gila monsters become increasingly dehydrated, they reduce activity to defend hydration state. The SDF behavior of Gila monsters appears to be largely driven by the fact that Gila monsters must separately satisfy energy and water demands with food and free-standing water, respectively, in conjunction with the timescale within which Gila monsters balance their energy and water budgets (supra-annually versus annually, respectively). Given these findings, the impact of anticipated changes in temperature and rainfall patterns in the Sonoran Desert are most likely going to pose their greatest risks to Gila monsters through the direct and indirect effects on water balance.
ContributorsWright, Christian (Author) / Denardo, Dale F. (Thesis advisor) / Harrison, Jon (Committee member) / McGraw, Kevin (Committee member) / Sullivan, Brian (Committee member) / Wolf, Blair (Committee member) / Arizona State University (Publisher)
Created2014
Description
For animals that experience annual cycles of gonad development, the seasonal timing (phenology) of gonad growth is a major adaptation to local environmental conditions. To optimally time seasonal gonad growth, animals use environmental cues that forecast future conditions. The availability of food is one such environmental cue. Although the importance of food availability has been appreciated for decades, the physiological mechanisms underlying the modulation of seasonal gonad growth by this environmental factor remain poorly understood.
Urbanization is characterized by profound environmental changes, and urban animals must adjust to an environment vastly different from that of their non-urban conspecifics. Evidence suggests that birds adjust to urban areas by advancing the timing of seasonal breeding and gonad development, compared to their non-urban conspecifics. A leading hypothesis to account for this phenomenon is that food availability is elevated in urban areas, which improves the energetic status of urban birds and enables them to initiate gonad development earlier than their non-urban conspecifics. However, this hypothesis remains largely untested.
My dissertation dovetailed comparative studies and experimental approaches conducted in field and captive settings to examine the physiological mechanisms by which food availability modulates gonad growth and to investigate whether elevated food availability in urban areas advances the phenology of gonad growth in urban birds. My captive study demonstrated that energetic status modulates reproductive hormone secretion, but not gonad growth. By contrast, free-ranging urban and non-urban birds did not differ in energetic status or plasma levels of reproductive hormones either in years in which urban birds had advanced phenology of gonad growth or in a year that had no habitat-related disparity in seasonal gonad growth. Therefore, my dissertation provides no support for the hypothesis that urban birds begin seasonal gonad growth because they are in better energetic status and increase the secretion of reproductive hormones earlier than non-urban birds. My studies do suggest, however, that the phenology of key food items and the endocrine responsiveness of the reproductive system may contribute to habitat-related disparities in the phenology of gonad growth.
Urbanization is characterized by profound environmental changes, and urban animals must adjust to an environment vastly different from that of their non-urban conspecifics. Evidence suggests that birds adjust to urban areas by advancing the timing of seasonal breeding and gonad development, compared to their non-urban conspecifics. A leading hypothesis to account for this phenomenon is that food availability is elevated in urban areas, which improves the energetic status of urban birds and enables them to initiate gonad development earlier than their non-urban conspecifics. However, this hypothesis remains largely untested.
My dissertation dovetailed comparative studies and experimental approaches conducted in field and captive settings to examine the physiological mechanisms by which food availability modulates gonad growth and to investigate whether elevated food availability in urban areas advances the phenology of gonad growth in urban birds. My captive study demonstrated that energetic status modulates reproductive hormone secretion, but not gonad growth. By contrast, free-ranging urban and non-urban birds did not differ in energetic status or plasma levels of reproductive hormones either in years in which urban birds had advanced phenology of gonad growth or in a year that had no habitat-related disparity in seasonal gonad growth. Therefore, my dissertation provides no support for the hypothesis that urban birds begin seasonal gonad growth because they are in better energetic status and increase the secretion of reproductive hormones earlier than non-urban birds. My studies do suggest, however, that the phenology of key food items and the endocrine responsiveness of the reproductive system may contribute to habitat-related disparities in the phenology of gonad growth.
ContributorsDavies, Scott (Author) / Deviche, Pierre (Thesis advisor) / Sweazea, Karen (Committee member) / McGraw, Kevin (Committee member) / Orchinik, Miles (Committee member) / Warren, Paige (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
Parental care provides many benefits to offspring. One widely realized benefit is enhanced regulation of offspring's thermal environment. The developmental thermal environment during development can be optimized behaviorally through nest site selection and brooding, and it can be further enhanced by physiological heat production. In fact, enhancement of the developmental thermal environment has been proposed as the initial driving force for the evolution of endothermy in bird and mammals. I used pythons (Squamata: Pythonidae) to expand existing knowledge of behavioral and physiological parental tactics used to regulate offspring thermal environment. I first demonstrated that brooding behavior in the Children's python (Antaresia childreni) is largely driven by internal mechanisms, similar to solitary birds, suggesting that the early evolution of the parent-offspring association was probably hormonally driven. Two species of python are known to be facultatively thermogenic (i.e., are endothermic during reproduction). I expand current knowledge of thermogenesis in Burmese pythons (Python molurus) by demonstrating that females use their own body temperature to modulate thermogenesis. Although pythons are commonly cited as thermogenic, the actual extent of thermogenesis within the family Pythonidae is unknown. Thus, I assessed the thermogenic capability of five previously unstudied species of python to aid in understanding phylogenetic, morphological, and distributional influences on thermogenesis in pythons. Results suggest that facultative thermogenesis is likely rare among pythons. To understand why it is rare, I used an artificial model to demonstrate that energetic costs to the female likely outweigh thermal benefits to the clutch in species that do not inhabit cooler latitudes or lack large energy reserves. In combination with other studies, these results show that facultative thermogenesis during brooding in pythons likely requires particular ecological and physiological factors for its evolution.
ContributorsBrashears, Jake (Author) / DeNardo, Dale (Thesis advisor) / Harrison, Jon (Committee member) / Deviche, Pierre (Committee member) / McGraw, Kevin (Committee member) / Smith, Andrew (Committee member) / Arizona State University (Publisher)
Created2012
Description
Theories of interval timing have largely focused on accounting for the aggregate properties of behavior engendered by periodic reinforcement, such as sigmoidal psychophysical functions and their scalar property. Many theories of timing also stipulate that timing and motivation are inseparable processes. Such a claim is challenged by fluctuations in and out of states of schedule control, making it unclear whether motivation directly affects states related to timing. The present paper seeks to advance our understanding of timing performance by analyzing and comparing the distribution of latencies and inter-response times (IRTs) of rats in two fixed-interval (FI) schedules of food reinforcement (FI 30-s and FI 90-s), and in two levels of food deprivation. Computational modeling revealed that each component was well described by mixture probability distributions embodying two-state Markov chains. Analysis of these models revealed that only a subset of latencies are sensitive to the periodicity of reinforcement, and pre-feeding only reduces the size of this subset. The distribution of IRTs suggests that behavior in FI schedules is organized in bouts that lengthen and ramp up in frequency with proximity to reinforcement. Pre-feeding slowed down the lengthening of bouts and increased the time between bouts. When concatenated, these models adequately reproduced sigmoidal FI response functions. These findings suggest that behavior in FI fluctuates in and out of schedule control; an account of such fluctuation suggests that timing and motivation are dissociable components of FI performance. These mixture-distribution models also provide novel insights on the motivational, associative, and timing processes expressed in FI performance, which need to be accounted for by causal theories of interval timing.
ContributorsDaniels, Carter W (Author) / Sanabria, Federico (Thesis advisor) / Brewer, Gene (Committee member) / Wynne, Clive (Committee member) / Arizona State University (Publisher)
Created2015
Description
Temporal bisection is a common procedure for the study of interval timing in humans and non-human animals, in which participants are trained to discriminate between a “short” and a “long” interval of time. Following stable and accurate discrimination, unreinforced probe intervals between the two values are tested. In temporal bisection studies, intermediate non-reinforced probe intervals are typically arithmetically- or geometrically- spaced, yielding point of subjective equality at the arithmetic and geometric mean of the trained anchor intervals. Brown et al. (2005) suggest that judgement of the length of an interval, even when not reinforced, is influenced by its subjective length in comparison to that of other intervals. This hypothesis predicts that skewing the distribution of probe intervals shifts the psychophysical function relating interval length to the probability of reporting that interval as “long.” Data from the present temporal bisection study, using rats, suggest that there may be a within-session shift in temporal bisection responding which accounts for observed shifts in the psychophysical functions, and that this may also influence how rats categorize ambiguous intervals.
ContributorsGupta, Tanya A. (Author) / Sanabria, Federico (Thesis advisor) / Wynne, Clive (Committee member) / McBeath, Michael (Committee member) / Arizona State University (Publisher)
Created2019
Description
Reproduction is energetically costly and seasonal breeding has evolved to capitalize on predictable increases in food availability. The synchronization of breeding with periods of peak food availability is especially important for small birds, most of which do not store an extensive amount of energy. The annual change in photoperiod is the primary environmental cue regulating reproductive development, but must be integrated with supplementary cues relating to local energetic conditions. Photoperiodic regulation of the reproductive neuroendocrine system is well described in seasonally breeding birds, but the mechanisms that these animals use to integrate supplementary cues remain unclear. I hypothesized that (a) environmental cues that negatively affect energy balance inhibit reproductive development by acting at multiple levels along the reproductive endocrine axis including the hypothalamus (b) that the availability of metabolic fuels conveys alterations in energy balance to the reproductive system. I investigated these hypotheses in male house finches, Haemorhous mexicanus, caught in the wild and brought into captivity. I first experimentally reduced body condition through food restriction and found that gonadal development and function are inhibited and these changes are associated with changes in hypothalamic gonadotropin-releasing hormone (GnRH). I then investigated this neuroendocrine integration and found that finches maintain reproductive flexibility through modifying the release of accumulated GnRH stores in response to energetic conditions. Lastly, I investigated the role of metabolic fuels in coordinating reproductive responses under two different models of negative energy balance, decreased energy intake (food restriction) and increased energy expenditure (high temperatures). Exposure to high temperatures lowered body condition and reduced food intake. Reproductive development was inhibited under both energy challenges, and occurred with decreased gonadal gene expression of enzymes involved in steroid synthesis. Minor changes in fuel utilization occurred under food restriction but not high temperatures. My results support the hypothesis that negative energy balance inhibits reproductive development through multilevel effects on the hypothalamus and gonads. These studies are among the first to demonstrate a negative effect of high temperatures on reproductive development in a wild bird. Overall, the above findings provide important foundations for investigations into adaptive responses of breeding in energetically variable environments.
ContributorsValle, Shelley (Author) / Deviche, Pierre (Thesis advisor) / McGraw, Kevin (Committee member) / Orchinik, Miles (Committee member) / Propper, Catherine (Committee member) / Sweazea, Karen (Committee member) / Arizona State University (Publisher)
Created2018
Description
The present series of studies examined whether a novel implementation of an
intermittent restraint (IR) chronic stress paradigm could be used to investigate hippocampal-dependent spatial ability in both sexes. In experiments 1 and 2, Sprague- Dawley male rats were used to identify the optimal IR parameters to assess spatial ability. For IR, rats were restrained for 2 or 6hrs/day (IR2, IR6, respectively) for five days and then given two days off, a process that was repeated for three weeks and compared to rats restrained for 6hrs/d for each day (DR6) and non-stressed controls (CON). Spatial memory was tested on the radial arm water maze (RAWM), object placement (OP), novel object recognition (NOR) and Y-maze. The results for the first two experiments revealed that IR6, but not IR2, was effective in impairing spatial memory in male rats and that task order impacted performance. In experiment 3, an extended IR paradigm for six weeks was implemented before spatial memory testing commenced in male and female rats (IR- M, IR-F). Unexpectedly, an extended IR paradigm failed to impair spatial memory in either males or females, suggesting that when extended, the IR paradigm may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not females, and that females appear to be resilient to spatial memory deficits in the face of chronic stress.
intermittent restraint (IR) chronic stress paradigm could be used to investigate hippocampal-dependent spatial ability in both sexes. In experiments 1 and 2, Sprague- Dawley male rats were used to identify the optimal IR parameters to assess spatial ability. For IR, rats were restrained for 2 or 6hrs/day (IR2, IR6, respectively) for five days and then given two days off, a process that was repeated for three weeks and compared to rats restrained for 6hrs/d for each day (DR6) and non-stressed controls (CON). Spatial memory was tested on the radial arm water maze (RAWM), object placement (OP), novel object recognition (NOR) and Y-maze. The results for the first two experiments revealed that IR6, but not IR2, was effective in impairing spatial memory in male rats and that task order impacted performance. In experiment 3, an extended IR paradigm for six weeks was implemented before spatial memory testing commenced in male and female rats (IR- M, IR-F). Unexpectedly, an extended IR paradigm failed to impair spatial memory in either males or females, suggesting that when extended, the IR paradigm may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not females, and that females appear to be resilient to spatial memory deficits in the face of chronic stress.
ContributorsPeay, Dylan (Author) / Conrad, Cheryl D. (Thesis advisor) / Bimonte-Nelson, Heather A. (Committee member) / Wynne, Clive (Committee member) / Arizona State University (Publisher)
Created2019
Description
The number of undergraduate students participating in short-term experiences in global health (STEGHs) abroad has increased dramatically in recent years (Eyler 2002, Drain et al. 2007). These experiences, in tandem with classroom learning, are designed to help students master skills related to global health competencies, including cultural humility and sensitivity, collaborating with community partners, and sociocultural and political awareness. Although STEGHs offer potential benefits to both students and to sending institutions, these experiences can sometimes be problematic and raise ethical challenges. As the number of students engaged in STEGHs continues to increase, it is important to better understand the impact of these programs on student learning. Current ethical and best practice guidelines for STEGHs state that programs should establish evaluation methods to solicit feedback from students both during and on completion of the program (Crump et al. 2010). However, there is currently no established method for gathering this feedback because of the many different global health competency frameworks, types and duration of programs, and different models of student engagement in such programs. Assessing the quality of a STEGH is a profoundly important and difficult question that cannot be answered as succinctly and quantitatively as classroom performance, which has more standard and established assessment metrics. The goal of this project is to identify the most appropriate and useful assessment metric(s) for determining educational quality and impact for STEGHs at ASU by comparing a typical quantitative evaluation tool (pre-post survey with brief open-ended questions) to a more in-depth qualitative method (key informant interviews). In performing my analysis I seek to examine if the latter can produce a richer narrative of student experiences to inform ongoing program evaluations. My research questions are: 1. What are the current qualitative and quantitative evaluation methods available to assess student learning during short-term experiences in global health? 2. How can current methodology for assessing student experiences with short-term experiences in global health be adapted to collect the most information from students? 3. How do student knowledge and attitudes change before and after their short-term experience in global health? Why is understanding those changes important for adapting programs? My end goal would be to use these new, optimal assessment methods for gathering student perspectives and experiences to adapt pre-departure trainings and post-experience debriefings for study abroad programs, both of which I believe will lead to more sustainable partnerships and a healthier understanding of global health work for students.
ContributorsHale, Brittany Ann (Author) / Jehn, Megan (Thesis director) / Wutich, Amber (Committee member) / School of Human Evolution and Social Change (Contributor) / School of Social Transformation (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05