Project ID: 2004CA90B

Title: Hydrological regimes, pond morphology, habitat use: predicting the impact of an emerging aquatic pathogen

Project Type: Research

Focus Categories: Invasive Species, Ecology

Keywords: amphibian declines, Batrachochytrium dendrobatidis, Mountain yellow-legged frogs, emerging disease, habitat use, Rana muscosa

Start Date: 03/01/2004

End Date: 02/28/2005

Federal Funds: $19,482

Non-Federal Matching Funds: $36,689

Congressional District: 44

Principal Investigator:
Cheryl Briggs

Abstract

1. Statement of the Critical Regional or State Water Research Problem
Amphibian populations throughout the world have been declining in recent years. Multiple interacting factors including disease, introduce species, habitat alteration, and climate change are contributing to the declines. Batrachochytrium dendrobatidis, a waterborne pathogen, which causes the fatal disease chytridiomycosis in amphibians, has recently appeared in the aquatic habitats of California and throughout the world. In portions of the Sierra Nevada mountains of California, the disease is causing massive die-offs of mountain yellow-legged frogs, Rana muscosa, a threatened native frog species. In other areas of the Sierra, infected populations of R. muscosa appear to be persisting with the disease. In the proposed study, we will investigate specific hypotheses to explain the different population-level outcomes of this waterborne pathogen in different California watersheds. The primary hypothesis is that differences in the pond morphology and topography of the landscape in the different sites result in differences in the frogs’ habitat use, altering their risk of acquiring and succumbing to the disease. Frogs that spend most of their time aggregated in the main lakes and ponds at each site, and in colder temperature habitats, are at greater risk from the disease. Alternative hypotheses are that differences in the transmission, infectivity, and/or virulence of the disease strains, or differences in susceptibility of the frog genotypes at the different types of sites, are leading to the observed population-level impacts of this water-borne pathogen.

2. Summary of research approach
Our proposed study has four main components: 1. A field survey of infected sites experiencing R. muscosa die-offs and infected sites persisting with the disease will be conducted. This will provide detailed information on the progression of the disease and its impact on R. muscosa populations, and will quantify and compare microhabitat characteristics at the different types of sites. 2. Field radio-tracking and mark-recapture studies will be performed to determine if frogs are using the habitat differently in the different types of sites, and if they are being exposed to higher temperatures at sites at which the populations are persisting with the disease. 3. Laboratory experiments will be carried out to compare the ecological characteristics of Batrachochytrium strains from die-off and persisting sites. Transmission rate, infectivity (as measured by zoospore release rate), and virulence of pathogen strains collected from die-off and persisting sites will be compared. 4. Laboratory experiments will be conducted to determine if there are genetic differences in susceptibility to the disease in the frog genotypes from die-off and persisting sites.

3. Statement of results, benefits and information expected from project
Emerging infectious diseases are a growing global threat to both wildlife and human populations. Rana muscosa populations in the watersheds of California’s Sierra Nevada Mountains are being threatened by a newly-identified fungal pathogen, Batrachochytrium dendrobatidis. The proposed study will provide crucial information on the factors that can lead to variation in the population-level impact of this water-borne pathogen. This information will be useful in helping to develop appropriate management strategies to protect this native amphibian species.

Progress/Completion Report PDF