Author ORCID Identifier

https://orcid.org/0000-0003-2524-088X

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Biology

First Advisor

Dr. Catherine R. Linnen

Abstract

My dissertation focuses on how differences accumulate across the genome during ecological speciation with geneflow. To do this I used two species of Neodiprionpine sawflies, which are plant-feeding hymenopterans with high host specificity. I used experimental crosses to measure both intrinsic and extrinsic postzygotic isolation and to understand the contribution of specific traits to reproductive isolation. Despite substantial genetic divergence and haploid males in which all recessive incompatibilities should be expressed, I found surprisingly little evidence of intrinsic postzygotic isolation. Recombination in hybrid males may reconstitute viable genotypes and counteract the effects of haploidy in males. Nevertheless, hybrids have drastically reduced fitness due to intermediate host-use traits causing strong extrinsic postzygotic isolation. Together, these results suggest that divergent selection on host-use traits is the primary driver of speciation in these, and likely other, plant-feeding insects.

Next, I performed a QTL mapping study of the traits under divergent selection that contribute to extrinsic postzygotic isolation to understand how genetic architecture can constrain or promote speciation and adaptation. I found that opposing dominance between host-choice and host-use traits composes the genetic basis of the earlier detected extrinsic postzygotic isolation. This opposing dominance is part of a growing body of work showing that trait mismatch and not hybrid intermediacy is typically how extrinsic postzygotic isolation is formed.

My fourth chapter focuses on how haplodiploid sex determination shapes how populations accumulate differences across the genome during speciation. Using a combination of demographic analysis of pine sawflies, population genetic simulations, and a meta-analysis, I found that compared to diploids, haplodiploids have predictably higher and more variable differentiation across the genome when they diverge in the presence of gene flow. Overall, Neodiprion sawflies present a great opportunity to better understand the genetics of adaptation and speciation.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.221

Funding Information

National Science Foundation: DEB-1257739 (2013-2017)

National Science Foundation: CAREER-175096 (2018-2023)

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