Document Type


Date of Degree Completion

Spring 2020

Degree Name

Master of Science (MS)



Committee Chair

Jason Irwin

Second Committee Member

Alison Scoville

Third Committee Member

Linda Raubeson


Single-nucleotide polymorphisms (SNPs) were used to assess the genetic connectivity of western toad (Anaxyrus boreas) breeding populations along Interstate-90 near Snoqualmie Pass, WA. Sites north and south of the freeway were sampled during the breeding season of 2019. SNP loci were subsequently generated using the proprietary DArTseqTM (Canberra, ACT, Australia) method. A total of 15,468 SNPs were used to calculate pairwise FST values and three distinct breeding populations were identified, two north and one south of I-90. All pairwise FST values between these sites were low (0.02) but significantly different from 0. The lowest pairwise FST was between the two sites that were furthest apart (11.6 km), indicating higher levels of connectivity along than across the freeway. A de novo discriminant analysis of principal components (DAPC) confirmed this division between sites on either side of I-90. Although I-90 is the most prominent potential barrier on the landscape, the Yakima River may also be contributing to this division. An a priori DAPC was able to distinguish between all populations with enough confidence to assign toads that were randomly encountered in the summer of 2019 to their most likely population of origin and will be a useful tool in future studies.