Browsing by Author "Norton, Andrew P., advisor"

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Open Access
Frameworks for testing mechanisms of invasion and plant defense
(Colorado State University. Libraries, 2018) Endriss, Stacy B., author; Hufbauer, Ruth A., advisor; Norton, Andrew P., advisor; Bowers, M. Deane, committee member; Ghalambor, Cameron K., committee member
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Open Access
Indirect effects in plant-pollinator interactions: the role of exotic plants and herbivores
(Colorado State University. Libraries, 2008) Cariveau, Daniel Paul, author; Norton, Andrew P., advisor
Flowering plants interact with a variety of other species. While numerous studies have demonstrated that pair-wise interactions between species are important factors affecting plant ecology and evolution, interaction with one species may affect the outcome of the interaction with another. I examined how pollination is influenced by both competition and herbivory. In Chapter One, I tested whether the presence of an exotic plant, musk thistle (Carduus nutans L. (Asteraceae)) influenced flower visitor behavior in relation to the native plant, bee balm (Monarda fistulosa L. (Lamiaceae)). I found that visitation rate to the native was not affected by the presence of the exotic. However, flower visitors commonly switched between the native and exotic and transferred exotic pollen to native plant stigmas. Conspecific pollen on the native plant stigmas was also reduced in the presence of the exotic. Seed set of the native plant was not affected. In a separate experiment, I examined how distance from the exotic plant influenced visitation rate to the native plant. I found that visitation rate to the native plant was reduced when the native plant was 1 and 5 meters from the exotic. However, visitation rate remained unchanged at 0 and 15 meters. This suggests that magnitude of interactions between plants through flower visitors may depend on spatial scale. In Chapter Two, I examined how the exotic plant, musk thistle, influenced visitation rate to the native plant, common harebell (Campanula rotundifolia L. (Campanulaceae)). I found that visitation rate to the native plant was reduced in the presence of the exotic plant. However, only solitary bees exhibited a reduction in visitation rate while Bombus species did not. Flower visitors did not switch between the exotic and native plants, and there were no exotic pollen grains on the native plant stigmas. Conspecific pollen deposition and seed set were not affected by the presence of the exotic plant. In Chapter Three, I explored whether the biological control Mecinus janthinus (Coleoptera) affected floral display size and visitation rate to the exotic plant Dalmatian toadflax (Linaria dalmatica (Scrophulariaceae)). In addition, I examined whether M. janthinus feeding affected female reproductive success directly or indirectly through flower visitors. I found that herbivory decreased the number of flowers and visitation rate to Dalmatian toadflax. However, I found no effect of herbivory on seed set when conducting hand-pollinations, suggesting no indirect effects of M. janthinus through flower visitors.
Open Access
Investigating ecological factors involved in the incidence and severity of Puccinia punctiformis infection in Cirsium arvense
(Colorado State University. Libraries, 2024) Astete Farfan, Almendra, author; Norton, Andrew P., advisor; Stewart, Jane E., advisor; Davis, Thomas Seth, committee member
The rust fungus Puccinia punctiformis has been proposed as a biocontrol agent against the widespread and noxious weed Cirsium arvense due to its specificity and ability to systemically infect and eventually kill C. arvense. However, the incidence of P. punctiformis is low in naturally infected systems. The environmental conditions of temperature and humidity to which P. punctiformis teliospores are exposed after production and until germination could affect their viability, and consequently, compromise the occurrence of infections. The first chapter of this thesis investigated teliospore viability for germination after exposure to different relative humidity (5 %, 22 %, 62 %, 90 % RH) and temperature levels (-20 °C, 6 °C, 23 °C) over the course of a year. Results showed that teliospore germinability decreases significantly faster when exposed to 23 °C and 62 % RH, or 90 % RH, followed by -20 °C and 5 % RH, compared to all other conditions. Teliospore priming is a stimulation process prior to germination that has been associated with increased germination in some rust fungi (Morin et al., 1992; Bruckart & Eskandari, 2002; Fisher et al., 2009). The second chapter examined how priming P. punctiformis teliospores, either in water or in a 250 µl/L solution of the germination stimulator dodecyl-NCS dissolved in water, influences their germinability, as well as the incidence and severity of systemic infection in C. arvense plants inoculated with the primed teliospores. Results showed that priming teliospores in water, without a germination stimulator, results in significantly higher germination rates compared to priming them in the 250 µl/L dodecyl-NCS solution. Furthermore, both priming treatments enable significantly greater germination proportions compared to not priming the teliospores. Statistically, the incidence and severity of the systemic infections caused by water-primed teliospores were not significantly different from those caused by teliospores primed in the 250 µl/L dodecyl-NCS solution. Ultimately, our findings suggest that environmental factors such as warm-humid and cold-dry conditions, reduce teliospore germinability. Consequently, these conditions can also limit P. punctiformis infection in C. arvense. For biocontrol purposes, we recommend to collect and store teliospores avoiding these adverse conditions to maximize their viability. Furthermore, we propose using water-primed teliospores for P. punctiformis inoculations on C. arvense, as they exhibited increased germination rates and may facilitate systemic infections in both axillar and new shoots.