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Mechanisms underlying host shift in cactophilic Drosophila

Crowley-Gall, Amber
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1553613245542061

Abstract Details

2019, PhD, University of Cincinnati, Arts and Sciences: Biological Sciences.
Divergent selective forces acting on populations as a result of varying ecological conditions, within the environments they inhabit, can lead to reproductive isolation and ultimately speciation. Host specialization in herbivorous insects provides a model to study this process as plants can vary in factors, such as abundance, flowering time, and diversity across an insect’s geographic range and this variation acts as a selective pressure on an insect’s ability to distinguish between available hosts. In recent years, multiple studies suggest that differences in volatile cues emitted by plants may result in differences in peripheral olfactory detection mechanisms that underlie variation in host preference behavior. The importance of this detection process, and its impacts on subsequent host preference behavior make it a useful model for examining mechanisms underlying adaptation to different ecological environments. This dissertation explores neurophysiological mechanisms, within the olfactory system, underlying host shift in cactophilic Drosophila. First, we examined variation in the olfactory system accompanying shifts to different host plants between two populations of Drosophila mojavensis, a species of fly consisting of four geographically isolated populations that each feed and breed on a different cactus species. We characterized the peripheral olfactory system and observed differences in the sensitivity and specificity of olfactory receptor neurons, as well as changes in their abundance between populations. Additionally, differential gene expression in members of the odorant receptor gene family was found between populations using RNA-seq. Variation in host plant availability and areas of host plant overlap exist within the D. mojavensis species range. Therefore, we next hypothesized that host plant availability would be associated with variation in neuronal response among localities within a given D. mojavensis population and that these differences would be associated with differences in odor-guided behavior. Results revealed within population differences in specificity and sensitivity of maxillary palp olfactory receptor neurons to volatiles found in cactus hosts. Specifically, in localities in which there was host plant overlap, D. mojavensis differed in its neuronal response to an ecological relevant volatile, 4-methylphenol. An association was observed between differences in these neuronal responses and odor-induced feeding behavior in the presence of 4-methylphenol. No association with oviposition or short-range olfactory behavior was found. Third, we examined if changes in odor sensitivity and/or selectivity acts as a mechanism for specialization on columnar cacti from an ancestral Opuntia host in the Drosophila repleta species group. The Drosophila repleta group, which includes D. mojavensis, consists of species that mainly that use Opuntia cactus as an ancestral host and has exhibited six independent shifts to specialize on more chemically complex columnar cacti species. We characterized odor response profiles of the ab2 sensillar subtype and found a distinct cluster of odor response profiles for columnar cactus specialists in the ab2B neuron. Each chapter of this dissertation further elucidates the role the peripheral olfactory system plays in the divergence of populations and species. Together, this dissertation work teases apart the mechanisms underlying divergence in olfactory preferences as well as adaptations associated with host specialization and varying ecological environments.
Stephanie Rollmann, Ph.D. (Committee Chair)
Elke Buschbeck, Ph.D. (Committee Member)
Brian Gebelein, Ph.D. (Committee Member)
Joshua Gross, Ph.D. (Committee Member)
John Layne, Ph.D. (Committee Member)
165 p.
Biology
olfaction; chemosensory; neurophysiology

Recommended Citations

Citations

  • Crowley-Gall, A. (2019). Mechanisms underlying host shift in cactophilic Drosophila [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1553613245542061

    APA Style (7th edition)

  • Crowley-Gall, Amber. Mechanisms underlying host shift in cactophilic Drosophila. 2019. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1553613245542061.

    MLA Style (8th edition)

  • Crowley-Gall, Amber. "Mechanisms underlying host shift in cactophilic Drosophila." Doctoral dissertation, University of Cincinnati, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1553613245542061

    Chicago Manual of Style (17th edition)

ucin1553613245542061
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This open access ETD is published by University of Cincinnati and OhioLINK.