<p>Plants commonly produce multiple, seemingly redundant defenses, but the reasons for this are poorly understood. The specificity of defenses to particular herbivores could drive investment in multiple defenses. Alternatively, genetic correlations between defenses could lead to their joint expression, even if possessing both defenses is non-adaptive. Plants may produce multiple defenses if putative resistance traits do not reduce damage, forcing plants to rely on tolerance of damage instead. Furthermore, resource shortages caused by herbivore damage could lead to compensatory changes in expression and selection on non-defense traits, such as floral traits. Natural selection could favor producing multiple defenses if synergism between defenses increases the benefits or decrease the costs of producing multiple defenses. Non-linear relationships between the costs and benefits of defense trait investment could also favor multiple defenses.</p><p>Passiflora incarnata (`maypop') is a perennial vine native to the southeast United States that produces both direct, physical traits (leaf toughness and trichomes) and rewards thought to function in indirect defense (extrafloral nectar in a defense mutualism with ants), along with tolerance of herbivore damage. I performed two year-long common garden experiments with clonal replicates of plants originating from two populations. I measured plant fitness, herbivore damage, and defense traits. I ran a genotypic selection analysis to determine if manipulating herbivore damage through a pesticide exclusion treatment presence mediated selection on floral traits, and if herbivore damage led to plastic changes in floral trait expression. To evaluate the role of selection in maintaining multiple defenses, I estimated fitness surfaces for pairwise combinations of defense traits and evaluated where the fitness optima were on each surface. </p><p>I found that resistance traits did not reduce herbivore damage, but plants demonstrated specific tolerance to different classes of herbivore damage. Tolerance was negatively correlated with resistance, raising the possibility that tolerance of herbivore damage instead of resistance may be the key defense in this plant, and that production of the two type of defense is constrained by underlying genetic architecture. Plants with higher levels of generalist beetle damage flowered earlier and produced proportionally more male flowers. I found linear selection for both earlier flowering and a lower proportion of male flowers in the herbivore exclusion treatment. I found that selection favored investment in multiple resistance traits. However, for two tolerance traits or one resistance and one tolerance trait, investment in only one trait was favored. </p><p>These results highlight the possibility of several mechanisms selecting for the expression of multiple traits, including non-defense traits. Resistance traits may have a non-defensive primary function in this plant, and tolerance may instead be a key defense strategy. These results also emphasize the need to consider the type of trait--resistance or tolerance--when making broad predictions about their joint expression.</p> / Dissertation

Doctor of Philosophy / Department of Plant Pathology / Bikram S. Gill / H13, a dominant resistance gene transferred from Aegilops tauschii into wheat (Triticum aestivum), confers a high level of antibiosis against a wide range of Hessian fly (HF, Mayetiola destructor) biotypes. Previously, H13 was mapped to the distal arm of chromosome 6DS, where it is flanked by markers Xcfd132 and Xgdm36. A mapping population of 1,368 F2 individuals derived from the cross: PI372129 (h13h13) / PI562619 (Molly, H13H13) was genotyped and H13 was flanked by Xcfd132 at 0.4cM and by Xgdm36 at 1.8cM. Screening of BAC-based physical maps of chromosome 6D of Chinese Spring wheat and Ae. tauschii coupled with high resolution genetic and Radiation Hybrid mapping identified nine candidate genes co-segregating with H13. Candidate gene validation was done on an EMS-mutagenized TILLING population of 2,296 M₃ lines in Molly. Twenty seeds per line were screened for susceptibility to the H13-virulent HF GP biotype. Sequencing of candidate genes from twenty-eight independent susceptible mutants identified three nonsense, and 24 missense mutants for CNL-1 whereas only silent and intronic mutations were found in other candidate genes. 5’ and 3’ RACE was performed to identify gene structure and CDS of CNL-1 from Molly (H13H13) and Newton (h13h13). Increased transcript levels were observed for H13 gene during incompatible interactions at larval feeding stages of GP biotype. The predicted coding sequence of H13 gene is 3,192 bp consisting of two exons with 618 bp 5’UTR and 2,260 bp 3’UTR. It translates into a protein of 1063 amino acids with an N-terminal Coiled-Coil (CC), a central Nucleotide-Binding adapter shared by APAF-1, plant R and CED-4 (NB-ARC) and a C-terminal Leucine-Rich Repeat (LRR) domain. Conserved domain analysis revealed shared domains in Molly and Newton, except for differences in sequence, organization and number of LRR repeat in Newton. Also, the presence of a transposable element towards the C terminal of h13 was indicative of interallelic recombination, recent tandem duplications and gene conversions in the CNL rich region near H13 locus. Comparative analysis of candidate genes in the H13 region indicated that gene duplications in CNL encoding genes during divergence of wheat and barley led to clustering and diversity. This diversity among CNL genes may have a role in defining differences in the recognition specificities of NB-LRR encoding genes. Allele mining for the H13 gene in the core collection of Ae. tauschii and hexaploid wheat cultivars identified different functional haplotypes. Screening of these haplotypes using different HF biotypes would help in the identification of the new sources of resistance to control evolving biotypes of HF. Cloning of H13 will provide perfect markers to breeders for HF resistance breeding programs. It will also provide an opportunity to study R-Avr interactions in the hitherto unexplored field of insect-host interaction.

abstract: Land management practices such as domestic animal grazing can alter plant communities via changes in soil structure and chemistry, species composition, and plant nutrient content. These changes can affect the abundance and quality of plants consumed by insect herbivores with consequent changes in population dynamics. These population changes can translate to massive crop damage and pest control costs. My dissertation focused on Oedaleus asiaticus, a dominant Asian locust, and had three main objectives. First, I identified morphological, physiological, and behavioral characteristics of the migratory ("brown") and non-migratory ("green") phenotypes. I found that brown morphs had longer wings, larger thoraxes and higher metabolic rates compared to green morphs, suggesting that developmental plasticity allows greater migratory capacity in the brown morph of this locust. Second, I tested the hypothesis of a causal link between livestock overgrazing and an increase in migratory swarms of O. asiaticus. Current paradigms generally assume that increased plant nitrogen (N) should enhance herbivore performance by relieving protein-limitation, increasing herbivorous insect populations. I showed, in contrast to this scenario, that host plant N-enrichment and high protein artificial diets decreased the size and viability of O. asiaticus. Plant N content was lowest and locust abundance highest in heavily livestock-grazed fields where soils were N-depleted, likely due to enhanced erosion and leaching. These results suggest that heavy livestock grazing promotes outbreaks of this locust by reducing plant protein content. Third, I tested for the influence of dietary imbalance, in conjunction with high population density, on migratory plasticity. While high population density has clearly been shown to induce the migratory morph in several locusts, the effect of diet has been unclear. I found that locusts reared at high population density and fed unfertilized plants (i.e. high quality plants for O. asiaticus) had the greatest migratory capacity, and maintained a high percent of brown locusts. These results did not support the hypothesis that poor-quality resources increased expression of migratory phenotypes. This highlights a need to develop new theoretical frameworks for predicting how environmental factors will regulate migratory plasticity in locusts and perhaps other insects. / Dissertation/Thesis / Ph.D. Biology 2012

Le genre de plantes carnivores à Nepenthes comporte au moins 120 espèces, réparties dans le sud est asiatique avec les iles de Bornéo et de Sumatra comme centres d'endémisme et de diversité. Ce sont des lianes, dont les feuilles modifiées en urnes comportent un faisceau d'adaptations physicochimiques et morphologiques qui concourent à l'attraction, la capture et la digestion d'arthropodes. La très grande diversité morphologique du genre est couplé e à une diversité fonctionnelle : les mécanismes de rétention sont variables d'une espèce à l'autre. A côté de cette diversité interspécifique, certaines espèces voient la morphologie et le fonctionnement de leurs urnes se modifier au cours de leur ontogénie. Cette thèse fait le lien entre les mécanismes du piégeage et l'écologie de quelques espèces et l'histoire évolutive et de la diversification du genre. / The carnivorous genus encompasses at least 120 species mainly distributed in SE Asia with Borneo and Sumatra recognized as endemism and diversity centers. They are vines whose leaves modified as pitchers exhibit an array of morphological and physicochemical adaptations that compete to the attraction, the capture and the digestion of arthropods. Besides the great morphological diversity the genus comprises a functional diversity exists: retentive mechanisms vary between species and in some species pitcher morphologies and functioning can also change throughout ontogeny. This thesis attempts to describe the trapping mechanisms and the ecology of some species to the evolutionary history of the diversification of the genus.

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Nitrogen (N) is an essential element to plants for growth, maintenance and reproduction, however most N does not exist in a form that is biologically available to plants. In order to maximise the acquisition and retention of N, plants have evolved a variety of morphological and physiological adaptations and life history strategies, as well as the ability to respond plastically to changes in resource availability in ecological time. Determining the ecophysiological responses of plants to changes in root N availability is crucial to further understanding of the mechanisms underlying competitive interactions between plants, and between plants and other organisms, that ultimately contribute to community structure and ecosystem functioning. Carnivorous plants are ideal systems for investigating ecophysiological responses to N availability as:- (i) they share a unique adaptation for obtaining supplemental N from captured prey, therefore ecological stoichiometry and energetic cost/benefit models may be explored; (ii) the trait of botanical carnivory is widely considered to have independently co-evolved as a response to N-deficient, sunny and wet environments, therefore resource allocation trade-offs between plant investment in N and carbon (C) acquisition may be observed, and (iii) they are extremely sensitive to changes in root N availability in ecological time. In this research, the carnivorous plant Drosera rotundifolia (round-leaved sundew) was used to address several unanswered ecophysiological and evolutionary questions relating to patterns and processes of prey capture and the N nutrition of carnivorous plants. Furthermore, the potential for reducing uncertainty in the calculation of plant reliance on carnivory using a δ15N natural abundance multi-level linear mixing model was explored. A combined approach of in-situ and ex-situ studies was employed, using co-occurring non-carnivorous plants or carnivorous plant species with differing evolutionary lineages or prey capture mechanisms respectively to provide context. Results show that the adaptations of carnivory, high reproductive investment and a relatively short life span enable Drosera rotundifolia to survive and thrive in an extreme, N deficient environment. Phenotypically plastic responses by the plant to light and root N availability provide evidence of resource allocation trade-offs between investment in carnivory for N acquisition and in photosynthesis for C acquisition. Plants invested less heavily in prey capture (measured as the stickiness of leaf mucilage) as N availability increased or light availability decreased. These results show that the energetic costs associated with carnivory are avoided by the plant when less costly sources of N are available for uptake and that the production of carbon-rich mucilage is only made under nutrient-limited and well-lit conditions. Results obtained from the comparison of captured insect prey with background invertebrates of potential prey indicate that Drosera rotundifolia is a dietary generalist, where the quantity of prey captured per plant is positively correlated with leaf stickiness and total leaf area. Plant reliance on prey-derived N decreased with increasing root N availability, providing evidence that carnivory is only of net benefit to the plant in N-deficient and well-lit environments, as the photosynthetic costs of investment in the trait are not exceeded by the energetic gain from prey N uptake in shady or dry habitats. A more accurate and precise method for calculating plant reliance on botanical carnivory is presented which incorporates the insect diet of the plant. This method has wider significance for reducing uncertainty in the calculation of relative source contributions to a mixture for most natural abundance applications using a multi-level linear mixing model. To conclude, results from this research further understanding of the ecophysiological mechanisms underlying plant responses to changes in resource availability and the selective pressures driving the evolution of plant adaptations. These results therefore assist with predicting how plants and plant communities may respond to sustained N deposition inputs and future environmental scenarios.

Doctor of Philosophy / Department of Entomology / Raymond A. Cloyd / James R. Nechols / Raymond A. Cloyd / James R. Nechols / Greenhouse studies were conducted to examine direct effects of light intensity and nitrogen source on primary and secondary metabolism of pac choi (Brassica rapa L. var. chinensis cv. ‘Mei Qing Choi’) and indirect effects on diamondback moth (Plutella xylostella L.)(DBM). In the first study, plants were exposed to high and low light intensities during different times of the year, resulting in a range of light intensities. From four experiments, plants exhibited higher phenolic content, greater shoot biomass, and higher C:N ratios under high light intensity, whereas plants under low light intensity contained higher protein. Ferulic acid increased under high light intensity, and this increase was negatively correlated with male DBM body weights. However, DBM developed faster on plants in the August experiment (high light), compared to the July experiment (lower light). This implies that light intensity may not be affecting DBM through plant-mediated changes unless reduced male weights confer a reduction in larval consumption. In the nitrogen source study, application of an organic source of nitrogen (fish hydrolysate fertilizer) was compared to a conventional fertilizer to determine whether nitrogen source directly impacts pac choi chemistry and biomass, thus indirectly impacting DBM fitness. In two experiments, there was no significant effect of fertility treatment on pac choi nutrients or biomass, with the exception of percent leaf phosphorus, which was significantly higher in the conventional fertility treatment. For DBM, percent survival and cohort development were significantly reduced on pac choi receiving the organic fertilizer. Calcium and magnesium were significantly higher in pac choi infested with DBM larvae than plants without DBM. In addition, calcium was negatively correlated with female DBM body weights in one experiment for the organic treatment. Overall, this study demonstrated that pac choi plants that received the organic fertilizer were similar to pac choi plants that received a conventional fertilizer with the exception of phosphorus. Furthermore, female DBM body weights were negatively impacted by calcium in the organic treatment. As multiple fitness traits for DBM were negatively affected in the organic treatment, pac choi crops grown with fish hydrolysate fertilizer may experience less feeding from DBM.