Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Co-chair

Winsor H. Lowe, Fred W. Allendorf

Commitee Members

Michael K. Schwartz


amphibians, Bufo boreas, chytridiomycosis, genetic variation


University of Montana


Amphibians are more threatened than any other vertebrate group, with 41% of species experiencing declines. The causes of most declines are not well understood, though many declines have been linked to the emerging infectious disease chytridiomycosis. Additionally, amphibians are physiologically constrained to moist habitats and considered poor dispersers; thus, they may suffer genetic consequences of population isolation. To address threats to the persistence of boreal toads (Bufo boreas) in Glacier National Park, USA, I genotyped 551 individuals at 11 microsatellite loci and used spatially independent (STRUCTURE) and spatially explicit (GENELAND) Bayesian methods to describe population genetic structure and identify barriers to gene flow. I found evidence of hierarchical population structure: individuals were splint into high and low elevation groups, and 2 secondary groups were detected within the high elevation group. These results indicate that elevation strongly influences genetic structure. Genetic variation was high, but allelic richness declined with increasing elevation. I tested a subset of the samples for Batrachochytrium dendrobatidis (Bd), the fungal pathogen which causes chytridiomycosis. Thirty-seven of 109 toads tested positive for Bd. Infection prevalence was not correlated with elevation, but—surprisingly—increased with individual heterozygosity. This finding suggests that dispersal may be facilitating the spread of disease because heterozygosity is highest where dispersal and gene flow are greatest.



© Copyright 2012 Brett Rebekah Addis