Date of Award

Spring 2009

Document Type



Life & Environmental Sciences

First Advisor

Jennifer Glowienka

Second Advisor

Grant Hokit

Third Advisor

Murphy Fox


Polymorphic pigmentation in natural populations has served as a model for understanding diversity and evolutionary change among populations. Melanism is a rare phenotype in garter snake populations that is used to study the adaptation of color and evolutionary processes associated with change in pigmentation among populations. Additionally, melanistic phenotypes can complicate species identification in situations of conservation interest. This study examined the association between phenotype and species of garter snakes found along the Missouri River near Townsend, MT by analyzing Cytochrome b mitochondrial DNA sequences of Thamnophis elegans (Western Terrestrial Garter Snake), T. sirtalis (Common Garter Snake), and melanistic individuals. Morphological evidence from a previous study suggests a close relationship between T. elegans and melanistic individuals. Taxon sampling and DNA extraction were conducted on the two known species and the melanistic individual. Maximum parsimony heuristic and bootstrap analyses and Neighbor-joining analyses were performed. The results showed that the melanistic snake sequences are more similar to sequences of T. elegans than to those of T. sirtalis and the melanistic snakes group with T. elegans in phylogenetic analyses. This study corroborates the findings from the morphological studies and contributes greatly to the understanding of Montana garter snake populations by confirming the species identification of melanistic individuals.