Date of Award

12-31-2018

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences/Environmental, Earth & Ocean Sciences

First Advisor

Helen Poynton

Second Advisor

Robert Bowen

Third Advisor

Alan Christian

Abstract

Insecticides are widely used in agricultural and urban settings throughout the United States. Driven by pre-exposure to pesticides, resistance to pyrethroid and organophosphate pesticides has been documented in populations of a nontarget amphipod, Hyalella azteca, in California. While genetic adaptive pyrethroid resistance in H. azteca has been attributed to two point mutations in the target site for pyrethroids, the voltage gated sodium channel (vgsc), the mechanism behind organophosphate resistance remained uninvestigated. The purpose of the present work was to better characterize the relationship between land use and adaptive pyrethroid resistance in wild populations of H. azteca while exploring the underlying mechanism(s) of resistance to organophosphates. Resistance screening was accomplished through the use of 96 h toxicity tests with a pyrethroid (cyfluthrin) and an organophosphate (chlorpyrifos) combined with target site resistance allele genotyping. Both pyrethroid and organophosphate resistance were common in populations of H. azteca near agricultural and urban terrestrial pesticide inputs in California, and that resistance was conferred through both previously-documented and novel point mutations in the target sites for these pesticide classes, the vgsc and acetylcholinesterase (ace-1) genes, respectively. Selection for resistance mutations was constrained in H. azteca, with at least ten independent origins of resistance alleles at three vgsc loci and three independent origins at one ace-1 locus, providing a unique example of the parallel evolution of pesticide resistance in a nontarget organism. Using the relationship between land use based variables and resistance alleles, a method was developed to target adaptive resistance in novel populations of H. azteca. Results showed that resistance to pyrethroids and organophosphates is common and predictable in H. azteca in at least two regions of the U.S. Watershed-level agricultural pesticide use indices and urban development successfully predicted whether resistance alleles would be detected in novel H. azteca populations, with urban land development often driving resistance. The present work provides a model system for the growing field of evolutionary toxicology and has implications for ecological risk assessment. Further, it strongly implicates urban pesticide use as a driver of aquatic ecosystem impairment.

Comments

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