Dissertation
Diversity and the evolution of host ranges in the North American oak gall wasps and their associated inquilines and parasitoids
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.17077/etd.006359
Abstract
A major question in evolutionary biology is why are there so many different species? Insects are one of the most diverse groups of animals with estimates of 1.5-3.0 million species worldwide. A large portion of insects are plant-feeding insects that have an intimate relationship with their hosts. Besides feeding on their host, they may find mates on or near the host, and lay eggs on or in the host, or have specialized behaviors that help them find specific host-related habitats. Changes in hosts have been documented as a mechanism that leads to reproductive isolation and can ultimately result in speciation. I studied a multi-tropic system centered around oak gall wasps and their parasites to investigate drivers of speciation and the role of host-shifts at different tropic levels. Oak gall wasps [Hymenoptera: Cynipidae: Cynipini] are a speciose group of wasps that oviposit into undifferentiated meristem of oak trees and induce the formation of a gall: an abnormal but often highly structured swelling of plant tissue. The gall provides nutrients to the developing gall wasp, and as an adult, the wasp will emerge from the gall by chewing an exit hole. The tree host, host location (e.g. stem, leaf, bud, flower, root) and morphology of the gall are gall wasp-species specific. The gall wasp and the gall itself are themselves host to a variety of other arthropod associates with the most common being parasitoids that attack the gall wasp and inquilines that utilize the gall tissue. I integrated field collections, morphology and DNA sequencing to: 1) describe the diversity of associates with oak galls specifically the inquiline genus Synergus, 2) determine the evolutionary history of Nearctic gall wasps, and 3) infer the role of host-shifts in this system at different tropic levels.
Through DNA sequencing, both single gene and reduced representation genome sequencing, I described the host ranges of a parasitoid species (Euderus set), several species in the inquiline genus Synergus, and a subset of the Nearctic gall wasps. In the inquiline genera Synergus, I found cryptic diversity within five previously described species and found an additional three undescribed species. I also sequenced five undescribed species of gall wasp and found preliminary evidence of cryptic diversity within known species that have genetic differentiation based on host association.
I also discovered important axes of specialization for parasitoids, inquilines, and the gall wasps. For the parasitoid wasp E. set, the most important characteristic was the host gall morphology, irrespective of how closely related the gall wasp hosts were. For the inquiline genus Synergus, species tended to specialize on oak tree taxonomic sections as well as galls that shared similar morphology. The gall wasps also specialized on oak taxonomic sections but also specialized on host organ (location of gall). The number of host-transitions within the gall wasp phylogeny suggests that host-shifts are key drivers of speciation in this clade.
Details
- Title: Subtitle
- Diversity and the evolution of host ranges in the North American oak gall wasps and their associated inquilines and parasitoids
- Creators
- Anna Katherine Glasson Ward
- Contributors
- Andrew Forbes (Advisor)John Logsdon (Committee Member)Maurine Neiman (Committee Member)Bryant McAllister (Committee Member)Andrew Kitchen (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Integrated Biology
- Date degree season
- Spring 2022
- DOI
- 10.17077/etd.006359
- Publisher
- University of Iowa
- Number of pages
- xiii, 156 pages
- Copyright
- Copyright 2022 Anna Katherine Glasson Ward
- Language
- English
- Description illustrations
- illustrations (chiefly color), tables, graphs
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
- Insects are one of the most speciose group of animals with estimates of 1.5-3 million species which begs the questions why are there so many species and what leads to the formation of new species? One mechanism for speciation is host-shifting, where shifting to a new host can cause reproductive isolation. I studied a species-rich group of insects – oak gall wasps and their parasitoid communities – to infer the role of host-shifting and other potential drivers of speciation. Oak gall wasps lay their eggs into plant tissues (primarily oak trees) and initiate the formation of a gall, an abnormal swelling of plant tissue that will provide the larvae with nutrients. Oak gall wasps are host to an even more speciose group of insect natural enemies that either attack the gall wasp or utilize the gall tissue. I integrated field collections, rearing of gall wasp and parasitoids, morphological identification, and DNA sequencing to 1) describe the diversity of an inquiline genus Synergus, 2) determine the evolutionary history of North American gall wasps, and 3) infer the role of host-shifts in this system at different tropic levels. I found cryptic diversity within the Synergus genus and found that species were often associated with galls with similar morphology. There have been multiple transitions of hosts in the evolutionary history of oak gall wasps. Overall, these findings suggest that host-shifting is broadly important to the origin of species for many different insects in these diverse oak gall communities.
- Academic Unit
- Biology
- Record Identifier
- 9984271053802771
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