Date of Award

Spring 2009

Document Type



Life & Environmental Sciences

First Advisor

Gerald Shields

Second Advisor

Jennifer Glowienka

Third Advisor

John Addis


This research applies the cytogenetic approach to investigate the reproductive status of a population of Simulium arcticum at the Clearwater River, Montana. Previous preliminary analysis at the site indicated: 1) the presence of two abundant taxa of the S. arcticum complex: IIL'3 and IIL'22, 2) a heterozygosity of at least 45% for the autosomal inversion IS'1, and 3) an abundance of larvae having polytene chromosomes of excellent quality. Since nothing was known about the reproductive status of the two prevalent taxa of S. arcticum at the Clearwater River prior to this study, I sought to gain insight into the -22 divergence process by testing the reproductive status of these taxa there. Since the IIL' cytotype has a very limited geographic distribution, I hypothesized that it would not be reproductively isolated from the more broadly distributed sibling, & arcticum sensu stricto (IIL'3). Of the 519 individuals analyzed, 17 different types existed although a majority (514 of the 519) was of the IIL'3 or IIL'22 types. About 80% were of the IIL'3 type and 20% were IIL’22. The distribution of genotypes for the IS'1 inversion indicated that these two types were in genetic equilibrium indicating that IIL' and IIL' are not reproductively isolated at the Clearwater River. This observation supports the Geographic Distribution/Taxon Age Hypothesis (Shields 2007). v