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Introduction
The mountain yellow-legged frog, Rana muscosa, was previously
abundant in lakes throughout the Sierras. In the last several decades its populations
have become fragmented due to the introduction of non-native trout, which
prey on frog eggs and tadpoles. The previously abundant frog populations
are now dwindling. In the last several years, a newly identified fungal
pathogen, Batrachochytrium dendrobatidis (B.d. for short), which causes the disease chytridiomycosis, has
been causing die-offs and local extinctions of R. muscosa, and has been affecting amphibians worldwide
See www.mylfrog.com
for more details about Rana muscosa
declines.
See www.amphibiaweb.org
for more information on amphibian declines, and amphibians in general.
Links for information
on amphibian chytridiomycosis:
http://amphibiaweb.org/chytrid/index.html
http://www.jcu.edu.au/school/phtm/PHTM/frogs/batrachochytrium.htm
http://lifesciences.asu.edu/irceb/amphibians/
B.d. Detection Methods:
We use a
non-invasive swabbing technique to detect B.d. in the field.
Our protocol, and a video
illustrating this technique are available on AmphibiaWeb.
We use the real-time (quantitative) PCR protocol outlined in the following
reference to analyze the samples for B.d.:
Boyle, D.G., Boyle, D.B., Olsen, V., Morgan, J.A.T., Hyatt, A.D. 2004.
Rapid quantitative detection of chytridiomycosis (Batrachochytrium dendrobatidis) in amphibian samples using real-time
Taqman PCR assay. Diseases of Aquatic Organisms 60(2):
141-148.
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Research
We are studying the impacts of Batrachochytrium
dendrobatidis (B.d.) on mountain yellow-legged frogs
in the California Sierra Nevada.
This includes field surveys,
which have shown that B.d. is
associated with extinction of R.
muscosa from hundreds of lakes in the Sierra, especially in the Sequoia
and Kings Canyon National Parks. In these lakes, previously large frog populations
are driven extinct within a few years of the first appearance of B.d. However, in Yosemite National Park and other northern areas, small
populations of R. muscosa are
apparently persisting with B.d. Mark-recapture
studies have shown that individuals
in these populations have low-level infections, but can survive between
years with the disease. We are
investigating the factors that might be contributing to these different population-level
outcomes. We are performing laboratory and field experiments
to quantify the disease transmission dynamics, and to determine the factors
that affect the impact of disease on individuals and populations. We are
developing spatially-explicit models
of the B.d./R. muscosa interaction. This
includes using population genetics
to quantify the scale of movement of the frogs and fungus.
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People
PI: Cherie Briggs,
Population modeling
co-PI’s: Roland
Knapp, Frog ecology and surveys
Craig Moritz, Frog
population genetics
John Taylor, Chytrid
biology and genetics
Postdoctoral Researchers:
Vance Vredenburg,
Frog dispersal, behavior and ecology
Erica Bree Rosenblum
Jess Morgan, now at Department of Primary
Industries and Fisheries
Martha Hoopes, now Assistant Professor, Mount Holyoke
College
Graduate Students:
John Parker, Amphibian pathology
Mary Stice, Frog immunology
Tate Tunstall, B.d. community impacts and/or genetics
Rob Bingham, Frog population genetics
Lara Rachowicz, PhD graduated, now at the National Park Service, Yosemite National Park
Research Assistants:
Eleanore Sternberg
Tina Cheung
Tom Smith
Undergraduate Researchers:
Many undergraduates have helped us with this project over the years,
including:
Alicia Bihler, Becky Chong,
Brianna Gaard, Kevin Gin, Ardeshir Jahanian, Yvonne Lee, Erika
Gisella Lin, Meile Liu, Shelly
Lyser, Kim Nguyen, Rosa Schneider, and Johnny
Yu
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Publications
Rachowicz, L.J.,
R.A. Knapp, J.A.T. Morgan, M.J. Stice, V.T.
Vredenburg, J.M. Parker and C.J. Briggs. In press. Emerging infectious
disease as a proximate cause of amphibian mass mortality in Rana muscosa populations. Ecology.
Rollins-Smith,
L.A., D.C. Woodhams,
L..K. Reinert, V.T.
Vredenburg, C.J. Briggs, P.F. Nielsen, and J.M. Conlon. In press. Antimicrobial
Peptide Defenses of the Mountain Yellow-Legged Frog (Rana muscosa). Developmental & Comparative
Immunology.
Knapp, R.A. and J.A.T. Morgan. In press. Tadpole mouthpart
depigmentation as an accurate indicator of chytridiomycosis,
an emerging disease of amphibians. Copeia.
Briggs, C.J, Vredenburg, V.T., Knapp, R.A., and L.
J. Rachowicz. 2005. Investigating the population-level effects of
chytridiomycosis, an emerging infectious disease of amphibians. Ecology,
86:3149–3159.
Rachowicz, L.J, J.M. Hero, J.A.T. Morgan, V.T. Vredenburg, J. Taylor,
C.J. Briggs. 2005. The novel and
endemic pathogen hypothesis: explanations for the origin of an emerging
infectious disease of wildlife. Conservation
Biology, 19(5):1441-1448.
Rachowicz, L.J. and V.T. Vredenburg.
2004. Transmission of Batrachochytrium
dendrobatidis within and between
amphibian life stages. Diseases of
Aquatic Organisms 61:75-83.
Vredenburg, V.T. 2004. Reversing
introduced species effects: Experimental removal of introduced fish leads
to rapid recovery of declining frog.
Proceedings of the National Academy of Sciences
101(20):7646-7650.
In review:
Rachowicz, L.J. and C. J. Briggs. In review. Quantifying the disease transmission function: Effects of density on Batrachochytrium
dendrobatidis transmission in the mountain yellow-legged frog (Rana
muscosa). Ecology.
Davidson, C., and R. A. Knapp.
In prep. A tale of two stressors: pesticides, fish, and the decline
of the mountain yellow-legged frog. Proceedings
of the National Academy of Sciences.
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Funding
This research was funded by:
NIH/NSF Ecology of Infectious
Disease Program grant
(funded by National Institute of Environmental Health Sciences).
R01 ES12067, “Amphibian
Disease Dynamics in a Fragmented Landscape”, $2,250,000,
2002-2007.
Additional funding for portions of the research was provided by:
UC Davis, Exotic/Invasive Pests and Diseases Research Program
UC Water Resources Center
California Department of Fish and Game
National
Park Service
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