Plant Hybridization Alters Arthropod Community Structure: Patterns Of Diversity And Abundance On Parental And Hybrid Cattails

Abstract

Hybridization creates novel genotypes that may differ from the parental species in traits that mediate ecological interactions. In plants, the response of insect communities to hybrid plants is of particular interest, with changes in insect abundance potentially feeding back on plant populations or having impacts on the higher trophic levels that rely on insects for food. In this project, I focused on cattails (Typha spp.), which are widespread, dominant wetland plants. In northern North America, the native cattail species T. latifolia hybridizes with T. angustifolia to form a distinct, vigorous form known as T. x glauca, which creates dense monocultures via vegetative growth, and is considered invasive. The goal of this research was to determine how arthropod communities respond to this hybrid plant, and to use one important insect species as a case study to uncover mechanisms determining insect abundance in cattail hybrid zones. Chapter 1 describes an extensive survey of the arthropod community assembling around cattail, and shows that diversity and abundance of arthropods is depauperate on the hybrid compared to T. latifolia, but similar to that on T. angustifolia. Abundance patterns differed by species, however, and certain important species showed depressed abundance on the hybrid compared to either parental species. One such species is the seed-eating moth Limnaecia phragmitella, and Chapters 2 and 3 explore potential mechanisms for why hybrid plants appear to have increased resistance to this herbivore. I show that female moths do not avoid hybrid plants as oviposition sites, and that poor larval performance due to food limitation (from reduced seed set) is the most likely mechanism driving this species' abundance pattern. Since low fertility is common in hybrid plants, low abundance of seed-feeding herbivores probably represents a predictable consequence of hybridization. Chapter 4 discusses identification of hybrid cattails, and presents sets of traits based on genetically-identified cattails that can be used by researchers and managers to distinguish first-generation hybrids from the parental species in the field. Overall, this research provides a valuable new perspective to questions surrounding the effects of hybridization on community ecology, and the role of hybridization in insect-plant interactions.