Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Erika Hersch-Green

Committee Member 1

Amy Marcarelli

Committee Member 2

Christopher Webster


Human activities have more than doubled the input rate of nitrogen to terrestrial ecosystems. Increased soil nitrogen availability is associated with increased plant productivity, changes in plant resource allocation strategies, and changes in interactions between plants and their associated insect herbivores. For example, nitrogen-rich conditions can alter the physiological and chemical properties of plants in ways that increase their ability to deter herbivore attack (resistance) and maintain fitness following herbivore attack (tolerance). The ecological tolerance of plants to such abiotic and biotic environments is thought to be influenced by autopolyploidy, a commonly occurring phenomenon in plants in which individuals have twice as many pairs of homologous chromosomes as other members from the same species. We examined the role of polyploidy in plants’ response to changes in soil nitrogen availability and insect herbivory. In two greenhouse experiments, we cultivated field collected genetic lines of diploid and autotetraploid Chamerion angustifolium (fireweed) under different soil nitrogen conditions and used a variety of insect-feeding experiments to examine whether polyploidy and soil nitrogen interact to influence (1) the growth, reproduction, and resource allocation of fireweed, and (2) the resistance and/or tolerance of fireweed to insect herbivory. Our results suggest that polyploidy influences reproductive output (e.g. flower and seed production) and resource allocation strategies (e.g. shoot:root ratio, C:N ratio) of fireweed, and that these differences can be dependent on soil nitrogen availability. The influence of polyploidy on patterns of resistance and tolerance of 7 fireweed to herbivory were complex. Tetraploids were more resistant to herbivory in some instances but less resistant in others, and these contrasting results were influenced by genotype, the type of insect herbivory, and the phenological age of plants. Despite ploidal differences in traits associated with plant tolerance (e.g. maximum photosynthetic capacity, shoot:root ratio), neither polyploidy nor soil nitrogen availability appeared to influence the tolerance of fireweed to herbivory. These experiments demonstrate the importance of polyploidy in regulating the relative success of plants responding to increased soil nitrogen availability and pressures from insect herbivores.