Effect of Amphibian Chytrid Fungus on the Size Distribution of Boreal Toads in Rocky Mountain National Park

Abstract

Amphibians have unique physical characteristics that increase their susceptibility to environmental disturbances. Their permeable skin and ectothermic manner of thermoregulation coupled with pathogen exposure are contributing factors to the global decline of amphibians. Additionally, most amphibians are biphasic, meaning they have two distinct habitat requirements over the course of their life. An aquatic environment is required for reproduction, while feeding and wintering as adults takes place on land. Amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), is a skin pathogen affecting amphibian populations globally, including the endangered populations of boreal toads in Rocky Mountain National Park (RMNP) in Colorado. We conducted population monitoring in tandem with size measurements of individual boreal toads found at two sites in RMNP. Lost Lake is a site that tests positive for Bd, (Fig. 1) and Spruce Lake is a site with no evidence of Bd (Fig. 2). Male and female toads found in the presence of Bd at Lost Lake had shorter snout-to-vent length (SVL) measurements and lower mass, suggesting that Bd may impact body size. Reproductive capacity may be altered by body size, so understanding the relationship between Bd and body size is important for species conservation of endangered boreal toads.