Browsing by Subject "hormesis"

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    Developmental influences on stress-based responses to environmental change
    (2023-05) Shephard, Alexander
    A central goal in ecology, evolution, and behavior (EEB) is to understand how individuals and populations respond to environmental change. Many forms of environmental change are stressful, leading to functional impairments, fitness declines, and loss of genetic diversity from natural populations. In this dissertation, I consider factors that explain why organisms vary in their abilities to tolerate stressful environments. Taking a developmental approach, I address this question in the context of three research domains within the broader field of EEB: (1) the evolution of phenotypic plasticity, (2) life history evolution and senescence, and (3) population responses to anthropogenic change. In data chapter 1, I use a nematode (Caenorhabditis elegans) to test the hypothesis that genetic variation in generalized plastic responses to stress is associated with reproductive costs. Consistent with a cost of plasticity, I find that genotypes capable of a higher degree of stress response plasticity exhibit lower reproductive performance under non-stressful conditions. In data chapter 2, I use migratory North American monarch butterflies (Danaus plexippus) to test how metabolic stress influences life history variation. I find that increased flight activity early in adulthood promotes butterfly longevity and somatic tissue antioxidant production, supporting the idea that metabolic stress is a driver of life history plasticity. In data chapters 3 – 7, I use two butterfly species, D. plexippus and Pieris rapae (the cabbage white), to test a range of hypotheses related to developmental mechanisms associated with tolerance to novel anthropogenic stressors such as heavy metal and salt pollution. In chapters 3 – 4, I find support for the hypothesis that variation in heavy metal tolerance is related to organismal condition (i.e., the total amount of energetic resources individuals can acquire throughout development). In Chapters 5 – 6, I ask how anthropogenic increases in nutrient availability influence the emergence of life history variation. In chapter 7, I show that heavy metal tolerance can vary among insect pollinator species, and I highlight the need for more research on heavy metal tolerance in species of conservation concern. Overall, this work, shows that considering developmental mechanism can help predict stress-based responses to environmental change among a range of disciplines within EEB.
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    Hormetic and Transgenerational Effects in Spotted-wing Drosophila (Diptera: Drosophilidae) in Response to Three Commonly-Used Insecticides
    (2022-03-14) Deans, Carrie; Hutchison, William; dean0179@umn.edu; Deans, Carrie; University of Minnesota Hutchison Lab
    Although insecticide formulations and spray rates are optimized to achieve lethal exposure, there are many factors in agricultural settings that can reduce the effective exposure of insect pests. These include weather patterns, timing of application, chemical degradation/volatilization, plant structural complexity, and resistant populations. While sub-lethal exposure to insecticides can still have negative impacts on pest populations, they can also lead to stimulatory, or hormetic, responses that can increase the fitness of surviving insects. Sub-lethal concentrations may also produce increased tolerance in the offspring of surviving adults through transgenerational effects. Sub-lethal effects are pertinent for the invasive fruit pest spotted-wing Drosophila, Drosophila suzukii Matsumura, because its small size, diurnal movement patterns, and utilization of hosts with complex plant structures, such as caneberries and blueberries, make effective insecticide applications tenuous. In this study, we measured spotted-wing Drosophila survivorship, reproductive performance, and offspring tolerance in flies exposed to sub-lethal concentrations of three commonly-used insecticides (zeta-cypermethrin, spinetoram, and pyrethrin). We found some evidence for hormesis, with survival effects being sex- and concentration-dependent for all insecticides. Males were far more susceptible to insecticides than females, which in some cases exhibited higher eclosion success and reproductive rates when exposed to sub-lethal doses. We did not observe significant transgenerational effects at sub-lethal concentrations, despite trends of increased offspring viability for zeta-cypermethrin and spinetoram. More research, however, is needed to fully understand the role that sub-lethal effects may play in pest population dynamics, insecticide efficacy, and the development of genetic resistance.