Pathogen invasion history elucidates contemporary host pathogen dynamics

Area of Science:

• Ecology
• Conservation Biology
• Pathogen Dynamics

Background:

• Amphibians are critically threatened, serving as indicators of global extinction events.
• Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is a major driver of amphibian decline.
• Understanding host-pathogen temporal dynamics is crucial for amphibian conservation.

Purpose of the Study:

• To reconstruct the historical invasion and spread of Batrachochytrium dendrobatidis (Bd) in Sierra Nevada amphibians.
• To investigate the temporal patterns of Bd invasion and their relationship to contemporary host-pathogen dynamics.
• To provide a temporal context for divergent amphibian population responses to Bd.

Main Methods:

• Analysis of 1165 amphibian specimens collected between 1900 and 2005 using a Bd qPCR assay.
• Historical reconstruction of Bd pathogen presence and prevalence across the Sierra Nevada.
• Comparison of Bd invasion timelines in central (Yosemite) versus southern (Sequoia/Kings Canyon) Sierra Nevada.

Main Results:

• Batrachochytrium dendrobatidis (Bd) infections were detected across the Sierra Nevada, with a significant increase in prevalence and spatial spread after the late 1970s.
• Evidence suggests multiple, near-simultaneous Bd invasions within regions, rather than a single wave-like pattern.
• Bd invasion occurred approximately four decades earlier in the central Sierra Nevada compared to the southern Sierra Nevada.

Conclusions:

• The temporal pattern of Bd invasion in the Sierra Nevada is complex, with distinct regional invasion timings.
• Divergent contemporary host-pathogen dynamics in Sierra Nevada frog populations may be explained by these varied invasion histories.
• Historical analysis of pathogen spread is vital for understanding current amphibian population trajectories and informing conservation strategies.