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- Genre: Doctoral Dissertation
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
Human-inhabited or -disturbed areas pose many unique challenges for wildlife, including increased human exposure, novel challenges, such as finding food or nesting sites in novel structures, anthropogenic noises, and novel predators. Animals inhabiting these environments must adapt to such changes by learning to exploit new resources and avoid danger. To my knowledge no study has comprehensively assessed behavioral reactions of urban and rural populations to numerous novel environmental stimuli. I tested behavioral responses of urban, suburban, and rural house finches (Haemorhous mexicanus) to novel stimuli (e.g. objects, noises, food), to presentation of a native predator model (Accipiter striatus) and a human, and to two problem-solving challenges (escaping confinement and food-finding). Although I found few population-level differences in behavioral responses to novel objects, environment, and food, I found compelling differences in how finches from different sites responded to novel noise. When played a novel sound (whale call or ship horn), urban and suburban house finches approached their food source more quickly and spent more time on it than rural birds, and urban and suburban birds were more active during the whale-noise presentation. In addition, while there were no differences in response to the native predator, rural birds showed higher levels of stress behaviors when presented with a human. When I replicated this study in juveniles, I found that exposure to humans during development more accurately predicted behavioral differences than capture site. Finally, I found that urban birds were better at solving an escape problem, whereas rural birds were better at solving a food-finding challenge. These results indicate that not all anthropogenic changes affect animal populations equally and that determining the aversive natural-history conditions and challenges of taxa may help urban ecologists better understand the direction and degree to which animals respond to human-induced rapid environmental alterations.
ContributorsWeaver, Melinda (Author) / McGraw, Kevin J. (Thesis advisor) / Rutowski, Ronald (Committee member) / Pratt, Stephen (Committee member) / Bateman, Heather (Committee member) / Deviche, Pierre (Committee member) / Arizona State University (Publisher)
Created2018
Description
The prevalence of obesity and obesity-related disorders have increased world-wide. In the last decade, the intestinal microbiome has become a major indicator of metabolic and gastrointestinal health. Previous research has shown that high-fat diet (HFD) consumption can alter the microbial composition of the gut by increasing the abundance of gram-positive bacteria associated with the onset of obesity and type 2 diabetes. Although, the most common form of obesity and metabolic syndrome intervention is exercise and diet, these recommendations may not improve severe cases of obesity. Thus, an important relevance of my project was to investigate whether the intake of an organometallic complex (OMC) would prevent the onset of metabolic and gastrointestinal complications associated with high-fat diet intake. I hypothesized that the consumption of a HFD for 6 weeks would promote the development of metabolic and gastrointestinal disease risk factors. Next, it was hypothesized that OMC treatment would decrease metabolic risk factors by improving insulin sensitivity and decreasing weight gain. Finally, I hypothesized that HFD-intake would increase the abundance of gram-positive bacteria associated with gastrointestinal disease. My preliminary data investigated the effects of a 6-week HFD on the development of hepatic steatosis, intestinal permeability and inflammation in male Sprague Dawley rats. I found that a 6-week HFD increases hepatic triglyceride concentrations, plasma endotoxins and promotes the production of pro-inflammatory cytokines in the cecum wall. I then investigated whether OMC treatment could prevent metabolic risk factors in male Sprague-Dawley rats fed a HFD for 10 weeks and found that OMC can mitigate risk factors such hyperglycemia, liver disease, impaired endothelial function, and inflammation. Lastly, I investigated the effects of a 10-week HFD on the gastrointestinal system and found an increase in liver triglycerides and free glycerol and alterations of the distal gut microbiome. My results support the hypothesis that a HFD can promote metabolic risk factors, alter the gut microbiome and increase systemic inflammation and that OMC treatment may help mitigate some of these effects. Together, these studies are among the first to demonstrate the effects of a soil-derived compound on metabolic complications. Additionally, these conclusions also provide an essential basis for future gastrointestinal and microbiome studies of OMC treatment.
ContributorsCrawford, Meli'sa Shaunte (Author) / Sweazea, Karen L (Thesis advisor) / Deviche, Pierre (Thesis advisor) / Al-Nakkash, Layla (Committee member) / Whisner, Corrie (Committee member) / Hyatt, Jon-Philippe (Committee member) / Arizona State University (Publisher)
Created2019
Description
The goal of this dissertation was to identify behavioral and physiological differences between urban and non-urban populations of wild birds, and to determine whether associations between oxidative balance and behavior are consistent across time and habitats. Urbanization is associated with a suite of unique stressors (e.g. pollution, habitat alteration) that might impose selection pressure on wildlife. Urban populations often differ from their non-urban counterparts behaviorally and physiologically, but patterns differ across species or cities, and few studies focus on multiple traits in the same individuals. Additionally, no study had before tested the correlation between behavior and oxidative balance across habitats. To address these questions, I first conducted a meta-analysis of the published literature to identify trends across studies on the effects of urbanization on oxidative balance in wild birds. This analysis showed that urban populations have higher oxidative stress and lower antioxidant capacity than rural populations, but that the effects of urbanization on oxidative damage can be species-specific. Second, I conducted studies on one focal species, the house finch (Haemorhous mexicanus), to identify correlates of oxidative balance measures and behavior. I found no evidence in support of the hypothesis that urban house finches experience oxidative stress. Instead, desert house finches had higher oxidative damage during the breeding season. Desert house finches also had lower stressed breathing rates during the breeding season, but urban house finches were more exploratory year-round. However, behavior and oxidative balance were minimally correlated and did not correlate across time. Juveniles had altered oxidative balance and were less exploratory than adults; no study had previously compared oxidative balance of recently fledged juveniles to adults. Finally, I identified shifts in oxidative balance measures in response to captivity. Plasma uric acid correlated with weight change in response to captivity. I identified novel differences between urban and desert finches, and reported that behavior and oxidative balance do not always correlate. My thesis illustrates the importance of sampling wild birds across contexts, including year, season, life stage, and captivity vs. field.
ContributorsPolekoff, Sarah (Author) / Deviche, Pierre (Thesis advisor) / McGraw, Kevin (Committee member) / Sweazea, Karen (Committee member) / DeNardo, Dale (Committee member) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2024
Description
Many animals thermoregulate to maximize performance. However, interactions with other animals, such as competitors or predators, limit access to preferred microclimates. For instance, an animal may thermoregulate poorly when fighting rivals or avoiding predators. However, the distribution of thermal resources should influence how animals perceive and respond to risk. When thermal resources are concentrated in space, individuals compete for access, which presumably reduces the thermoregulatory performance while making their location more predictable to predators. Conversely, when thermal resources are dispersed, several individuals can thermoregulate effectively without occupying the same area. Nevertheless, interactions with competitors or predators impose a potent stress, often resulting in both behavioral and physiological changes that influence thermoregulation. To assess the costs of intraspecific competition and predation risk during thermoregulation, I measured thermoregulation, movement, and hormones of male lizards (Sceloporus jarrovi) in experiment landscapes, with clumped to patchy distributions of microclimates. I found lizards aggressively competed for access to microclimates, with larger males gaining priority access when thermal resources were aggregated. Competition reduced thermoregulatory performance, increased movements, and elevated plasma corticosterone in large and small males. However, the magnitude of these responses decreased as the patchiness of the thermal environment increased. Similarly, under simulated predation risk, lizards reduced thermoregulatory performance, decreased movements, and elevated plasma corticosterone. Again, with the magnitude of these responses decreased with increasing thermal patchiness. Interestingly, even without competitors or predators, lizards in clumped arenas moved greater distances and circulated more corticosterone than did lizards in patchy arenas, indicating the thermal quality of the thermal landscape affected the energetic demands on lizards. Thus, biologists should consider species interactions and spatial structure when modeling impacts of climate change on thermoregulation.
ContributorsRusch, Travis W (Author) / Angilletta, Michael (Thesis advisor) / Sears, Mike (Committee member) / DeNardo, Dale (Committee member) / Deviche, Pierre (Committee member) / McGraw, Kevin (Committee member) / Arizona State University (Publisher)
Created2017
Description
Understanding the drivers of diet selection by carnivores is key for wildlife conservation and management, particularly in the Anthropocene. Yet, most assessments of predation do not consider how spatio-temporal prey availability or nutrition influence carnivore diet selection. Using a novel data integration approach for camera trap and scat data, I assessed how spatial and temporal components of prey availability influenced diet selection by bobcats (Lynx rufus) in Colorado, USA (Chapter 1) and coyotes (Canis latrans) in Arizona, USA (Chapter 2) in areas of low and moderate levels of urbanization. I also assessed coyote diets using the nutritional geometric framework to determine coyote macronutrient consumption seasonally and relative to urbanization (Chapter 3). My results suggest that cottontail rabbit availability largely drove bobcat predation, and that bobcats consumed prey relative to its availability overall and in wildland areas, but that this relationship weakened in anthropogenic regions. I also found that, overall, models of prey availability that incorporated the temporal overlap between predator and prey taxa predicted bobcat diet selection better than models assessing the spatial availability of prey. Similarly, I found coyotes consumed prey relative to its availability overall and in sites with lower levels of human influence across seasons, but not in moderately urbanized sites. I also found that models of prey availability that incorporated time better predicted coyote diets compared to models assessing the spatial availability of prey. Finally, I observed that the macronutrient composition of coyote diets was similar between moderately and less urbanized sites, particularly in the spring-summer season. However, coyote macronutrient consumption differed seasonally, with coyotes eating more non-protein energy relative to protein energy when carbohydrate-rich mesquite (Prosopis spp.) was more available in the fall-winter. In addition, the consistently high consumption of lipid-rich domestic cats in moderately urbanized sites further supports the hypothesis that coyotes increased their consumption of non-protein energy when available and when assuming protein needs were already met. This dissertation provides new insights into how urbanized landscapes impact carnivore ecology. Since diet selection drives many human-carnivore conflicts, this research can also be used to help inform wildlife management and decision-making in anthropogenic areas.
ContributorsWeiss, Katherine (Author) / Sterner, Beckett (Thesis advisor) / Schipper, Jan (Thesis advisor) / Deviche, Pierre (Committee member) / Lewis, Jesse S (Committee member) / Strauss, Eric G (Committee member) / Arizona State University (Publisher)
Created2024
Description
In wild birds, the stress response can inhibit the activity of the innate immune system, which serves as the first line of defense against pathogens. By elucidating the mechanisms which regulate the interaction between stress and innate immunity, researchers may be able to predict when birds experience increased susceptibility to infections and can target specific mediators to mitigate stress-induced suppression of innate immune activity. Such elucidation is especially important for urban birds, such as the House Sparrow (Passer domesticus), because these birds experience higher pathogen prevalence and transmission when compared to birds in rural regions. I investigated the role of corticosterone (CORT) in stress-induced suppression of two measures of innate immune activity (complement- and natural antibody-mediated activity) in male House Sparrows. Corticosterone, the primary avian glucocorticoid, is elevated during the stress response and high levels of this hormone induce effects through the activation of cytosolic and membrane-bound glucocorticoid receptors (GR). My results demonstrate that CORT is necessary and sufficient for stress-induced suppression of complement-mediated activity, and that this relationship is consistent between years. Corticosterone, however, does not inhibit complement-mediated activity through cytosolic GR, and additional research is needed to confirm the involvement of membrane-bound GR. The role of CORT in stress-induced inhibition of natural antibody-mediated activity, however, remains puzzling. Stress-induced elevation of CORT can suppress natural antibody-mediated activity through the activation of cytosolic GR, but the necessity of this mechanism varies inter-annually. In other words, both CORT-dependent and CORT-independent mechanisms may inhibit natural antibody-mediated activity during stress in certain years, but the causes of this inter-annual variation are not known. Previous studies have indicated that changes in the pathogen environment or food availability can alter regulation of innate immunity, but further research is needed to test these hypotheses. Overall, my dissertation demonstrates that stress inhibits innate immunity through several mechanisms, but environmental pressures may influence this inhibitory relationship.
ContributorsGao, Sisi (Author) / Deviche, Pierre (Thesis advisor) / DeNardo, Dale (Committee member) / McGraw, Kevin (Committee member) / Orchinik, Miles (Committee member) / Moore, Michael C. (Committee member) / Arizona State University (Publisher)
Created2017
Description
Birds have the highest blood glucose concentrations of all vertebrates. Meanwhile, birds do not develop the same physiological complications (e.g., increased oxidative stress and glycation) that mammals do when blood glucose is elevated (i.e., diabetes). Therefore, birds may serve as a negative model animal for hyperglycemic complications. The physiological reason for high blood glucose in birds remains largely unknown although several unique characteristics of birds may contribute including a lack of the insulin responsive glucose transport protein, relatively high glucagon concentrations, as well as reliance on fatty acids to sustain the high energetic demands of flight. In breaking down triglycerides for energy, glycerol is liberated, which can be converted to glucose through a process called gluconeogenesis. In addition, the extent to which birds maintain homeostatic control over blood glucose in response to extreme dietary interventions remains unclear and few dietary studies have been conducted in wild-caught birds. Using Mourning Doves (Zenaida macroura) as a model organism, this dissertation tests four hypotheses: 1) Gluconeogenesis contributes to high circulating blood glucose concentration; 2-4) similar to mammals, a fully refined carbohydrate (i.e., white bread diet); a high saturated fat diet (60% kcal from fat); and an urban-type diet comprised of a 1:1 ratio of French fries and birds seed will increase blood glucose compared to a nutritionally-balanced diet after a four-week duration. Contrary to the hypothesis, 150 mg/kg Metformin (which inhibits glycerol gluconeogenesis) increased blood glucose, but 300 mg/kg resulted in no change. However, when 2.5 mg/kg of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB; a glycogenolysis inhibitor) was given with 150 mg/kg of Metformin, blood glucose was not different from the control (50 ul water). This suggests that glycerol gluconeogenesis does not contribute to the naturally high blood glucose in birds and that a low dose of Metformin may increase the rate of glycogenolysis. In addition, all three experimental diets failed to alter blood glucose compared to control diets. Collectively, these results suggest that, in addition to a negative model for diabetes complications, birds can also serve a negative model for diet-induced hyperglycemia. Future research should further examine dietary manipulation in birds while controlling for and examining different variables (e.g., species, sex, duration, diet composition, urbanization).
ContributorsBasile, Anthony Joseph (Author) / Sweazea, Karen L (Thesis advisor) / Deviche, Pierre (Committee member) / Johnston, Carol (Committee member) / Trumble, Ben (Committee member) / Parrington, Diane J (Committee member) / Arizona State University (Publisher)
Created2022