Aboveground effects of variation in the legume-rhizobium mutualism on insect herbivore Spodoptera exigua

Anthropogenic nitrogen deposition is a significant threat to many natural ecosystems. There is evidence that increased N deposition negatively affects an ecologically important resource mutualism, the legume-rhizobium mutualism, by inciting the evolution of less-cooperative strains of N-fixing rhizobia bacteria. The arising of less-cooperative rhizobia has the potential to influence higher trophic levels, since plant and animal communities depend on the biologically-fixed N that this mutualism provides. This study aimed to evaluate the effect of the evolution of variable mutualist quality rhizobium strains on the nutrition of clover (Trifolium hybridum) tissues and the survival and development of generalist insect herbivore Spodoptera exigua on clover inoculated with high- and low-quality partner rhizobia. I found that inoculation with low-quality rhizobia increases the carbohydrate content in clover leaf tissues and decreases S. exigua survival. Inoculation with high-quality rhizobia, conversely, does not appear to improve protein content available to herbivores in plant tissues, but does improve S. exigua survival and some developmental metrics. Herbivores fed leaves from uninoculated, fertilized plants had decreased survival compared to herbivores fed leaves from plants inoculated with high-quality partners, implying that N deposition into ecosystems does not fully replace nutrients provided by rhizobia. These results suggest that evolution of variable mutualist quality rhizobia has consequences for higher trophic levels, and that increased N deposition has the potential to disrupt not only plant populations but whole communities and ecosystems via the breakdown of the legume-rhizobium mutualism.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Entomology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Wargin, Annaliese H.

Contributors dc:contributor

• Harmon-Threatt, Alexandra
• Dolezal, Adam
• Heath, Katy

• Mutualism
• Multi-trophic Interactions
• Plant-insect Interactions
• Fabaceae
• Herbivory

Statement dc:rights

• Copyright 2023 Annaliese Wargin

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120136

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120136