STRESSFUL MEMORIES: CONSEQUENCES OF HERBIVORY AND INBREEDING IN SOLANUM CAROLINENSE

Open Access
- Author:
- Nihranz, Chad T
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 03, 2018
- Committee Members:
- Andrew George Stephenson, Dissertation Advisor/Co-Advisor
Andrew George Stephenson, Committee Chair/Co-Chair
John Frazier Tooker, Committee Member
James Homer Tumlinson III, Committee Member
Gary Felton, Outside Member
Mark C. Mescher, Special Member - Keywords:
- Solanum carolinense
Manduca sexta
herbivory
induced defenses
inbreeding
transgenerational induction - Abstract:
- This dissertation focuses on understanding the effects of maternal plant inbreeding and previous generation herbivory on fitness- and defense-related traits in an agriculturally important weed, Solanum carolinense. To address the effects of herbivory and inbreeding on plant phenotypes across growing seasons and across generations, I designed an elaborate breeding system where I created (1) rhizomes from inbred and outbred plants that had either experienced herbivory or were left undamaged (used in chapter 2) and (2) outbred seeds produced from herbivore-damaged and undamaged maternal inbred and outbred plants (used in chapters 3 and 4). While some research has focused on the effects of herbivory on plant offspring phenotypes, to the best of my knowledge this dissertation is the first to comprehensively examine (1) if a memory of herbivory can be transmitted through the rhizome and seed of a plant, (2) if this herbivore-induced memory affects plant growth, reproduction, defenses, and herbivore resistance in next-season offshoots and offspring grown from seed, and (3) whether plant inbreeding alters such herbivore-induced effects on offspring phenotypes. In chapter 2, I address the effects of maternal plant herbivory, inbreeding, and rhizome overwintering on the growth, reproduction, and defense-related traits of rhizomatous offshoots of S. carolinense. My data show that a memory of maternal plant herbivory can persist in unconnected rhizomatous offshoots and that this memory positively impacts offshoot defenses against herbivores. Specifically, I found that offshoots of herbivore-damaged plants had a greater leaf trichome and internode spine density and that caterpillar larvae performed less well on the leaves of offshoots from damaged plants than on the leaves of offshoots of undamaged plants. Furthermore, I found an apparent trade-off associated with increased defenses in plant offshoots. Rhizomatous offshoots of herbivore-damaged plants emerged later, flowered later, and produced fewer flowers than offshoots of undamaged plants. I also found that offshoots of outbred plants had a greater leaf trichome density than offshoots of inbred plants when damaged by herbivores, indicating that inbreeding may compromise induced defenses against herbivores in rhizomatous offshoots across growing seasons. In chapter 3, I examine the transgenerational effects of herbivory and maternal plant inbreeding on fitness-related traits in outbred S. carolinense grown from seed. This study addresses the effects of previous generation herbivory and maternal plant inbreeding on the growth and reproduction of S. carolinense offspring in the greenhouse and field. I found that offspring of herbivore-damaged plants had a greater rate of seedling emergence, flowered earlier, and produced more flowers than offspring of undamaged plants when grown under greenhouse conditions. While I did not find any effects of previous generation herbivory on offspring flower production or fruit production in the field, my data do indicate that offspring of damaged parent plants produced more seeds in the field than offspring of undamaged plants. I also found that offspring of inbred maternal plants had lower seedling emergence in the greenhouse and produced fewer flowers and fruit in the field than offspring of outbred maternal plants, indicating that maternal plant inbreeding can have prolonged negative effects on plant growth and reproduction in outbred offspring. In chapter 4, I address the transgenerational effect of herbivory on the defensive phenotype of S. carolinense offspring. I also tested whether maternal plant inbreeding affects offspring defenses against herbivores and if inbreeding compromises the ability of plants to impart a transgenerational memory of herbivory to their offspring. Specifically, I assessed the transgenerational effects of herbivory and maternal plant inbreeding on offspring trichome density, internode spine production, the production of volatile organic compounds (VOC) that are known to attract predaceous insects, and jasmonic acid (JA) concentrations and the expression of JA-associated genes, which are known to mediate the production of plant defenses against chewing insects. Furthermore, I examined the transgenerational effects of herbivory and maternal plant inbreeding on herbivore performance traits. My data show that offspring of herbivore-damaged plants had greater constitutive leaf trichome and internode spine production than offspring of undamaged plants, and that herbivore development was delayed when caterpillars fed on offspring of herbivore-damaged plants. I also found that maternal plant inbreeding adversely affected offspring defensive phenotypes and resistance to herbivores, even though the offspring were outbred. I did not find any transgenerational effects of herbivory or maternal plant inbreeding on constitutive or induced VOC blends, JA concentrations, or the expression of JA-associated genes. Taken together, these findings illustrate that insect herbivory and maternal plant inbreeding can have considerable effects on growth, reproduction, and anti-herbivore defenses in rhizomatous offshoots and sexually produced offspring of Solanum carolinense. This dissertation also demonstrates further consequences of inbreeding on plant fitness and defenses against herbivores that can extend across generations.