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A Yosemite toad in its burrow.
Photo Credit: Sara Hilary Gabel / National Park Service
Scientific Frontline: Extended "At a Glance" Summary: Winter Propagation of Batrachochytrium dendrobatidis in Yosemite Toads
The Core Concept: The fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the fatal amphibian disease chytridiomycosis, has been discovered to rapidly proliferate on threatened Yosemite toads (Anaxyrus canorus) during their winter hibernation in underground burrows, contrary to the previous belief that transmission and growth occurred primarily in aquatic environments during warmer breeding seasons.
Key Distinction/Mechanism: While Bd is largely considered an aquatic pathogen that grows optimally in moderate temperatures, this research reveals its capacity to multiply aggressively on terrestrial hosts under near-freezing conditions during dormancy, potentially due to the amphibians' significantly suppressed immune function during hibernation.
Major Frameworks/Components:
- Pathogen Screening: Utilization of polymerase chain reaction (PCR) tests on skin swabs to quantify fungal loads across different seasons and life stages.
- Overwintering Dynamics: Analysis of Bd prevalence in juvenile toads (metamorphs) before entering and immediately after emerging from subterranean winter dormancy.
- Host-Pathogen-Environment Interaction: Investigating the interplay between cold temperatures, burrow microclimates, and amphibian immune depression in facilitating pathogen growth.


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