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Date Permissions Signed


Date of Award

Spring 2022

Document Type

Masters Thesis

Department or Program Affiliation


Degree Name

Master of Science (MS)



First Advisor

Schwarz, Dietmar, 1974-

Second Advisor

Peterson, Merrill A., 1965-

Third Advisor

Bunn, Andrew Godard


Species with broad distributions exist in heterogenous landscapes and therefore must be able to maintain key physiological processes under a variety of abiotic conditions. This can lead to localized variation in phenotypes associated with environmental cues. Atmospheric water loss is a major source of physiological stress for terrestrial insects and one which is predicted to have major implications for biodiversity under future climate scenarios. Understanding which species exhibit adaptive variation can provide crucial insights into how individual species and thus ecological communities have evolved to cope with changing climate conditions as well as inform predictions as to how they may adapt to future climates. These adaptions can also introgress into non-native congeners via hybridization and allow introduced species to become increasingly invasive.

In this study I investigate variation in desiccation resistance of larval and early pupal Rhagoletis zephyria, a widespread endemic species within the Pacific Northwest. The region is characterized by mesic coastal conditions west of the Cascade Range and xeric steppe and pine forests to the east, of which both eastern and western biomes are home to R. zephyria and its obligate plant host, Symphoricarpos albus. Wild-collected larvae from across the region were subjected to desiccation treatment during the early pupal life stage, with desiccation resistance assessed via weight retention following exposure. Modeling with machine learning algorithms and regional bioclimate variables demonstrated that most of the regional variation in desiccation response could be predicted by regional bioclimate, with increased weight retention in areas with increased evapotranspiration and decreased winter precipitation. This prediction was constrained to areas deemed suitable to the host plant via species distribution modeling in MaxEnt. The modeling identified likely regions of dramatic variation in desiccation resistance along localized bioclimate gradients, suggesting that the localized selection pressure on this response is very strong and/or that the response is plastic. While this study design does not allow distinction to be made between these two forms of variation in response to climate cues, the presence of adaptive variation in response to localized desiccation stress in the evolutionarily and economically important Rhagoletis genus is shown here for the first time.




Western Washington University

OCLC Number


Subject – LCSH

Insects--Adaptation--Northwest, Pacific; Insect-plant relationships--Northwest, Pacific; Insect--Climatic factors--Northwest, Pacific; Entomology--Research

Geographic Coverage

Northwest, Pacific




masters theses




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