INTERACTIVE IMPACTS OF A FUNGAL
PATHOGEN AND TEMPERATURE ON
MOUNTAIN AMPHIBIANS
Karen Pope
Jonah Piovia-Scott
Outline
I.
II.
Disease and amphibians
Current hypotheses about
climate and amphibian
chytridiomycosis
Introduction to our study
system
III.
I.
II.
IV.
V.
Klamath Mtns, CA
Southern Cascades, CA
Findings and directions
Implications
Climate Change and Emerging
Infectious Diseases
• EIDs are increasing with climate
change
• Spread of vector organisms
• Reduced resistance of host
• Temperate latitudes
Patz et al. 2005. Nature. Correlation between
simulated, climate-driven variations in
mosquito density and observed variations in
dengue fever cases.
Amphibian Declines
• Sixth extinction event
• Amphibians most “at risk” vertebrate taxa
• Reasons
– Habitat loss
– Invasive species
– Contaminants
– Climate change
– Disease
Amphibian Chytridiomycosis
• Batrachochytrium dendrobatidis (Bd)
• Greatest loss of vertebrate biodiversity
attributable to disease - IUCN
• Disrupts epidermal function in frogs
• Effects variable
Bd Lifecycle
Global Distribution
Fisher et al. 2009
Characteristics of Susceptibility
• Cool climates (< 25° C)
• Aquatic life history
• Lack skin defenses
Climate and Spread
General debate about whether climate change is
driving the disease
– Pounds et al. Nature. 2006- “Climate-linked
epidemic hypothesis” and “Chytrid-thermaloptimum hypothesis”
– Lips et al. PLOS. 2008. “Spatiotemporal spread
hypothesis”.
– Rohr and Raffel. PNAS. 2010. “Climate-variability
hypothesis”
Climate and Virulence
• Strong evidence that temperature affects
virulence
– Lab (> 4°C, < 28°C)
– Field: low elevation vs. high elevation
(e.g., Mountain yellow-legged frog)
Wake and Vredenburg 2008
Our Study System – Klamath Mtns and
Southern Cascades, CA
•
•
•
•
Intermediate elevations
Intermediate temperature regime
Bd present
High amphibian diversity
Lentic Amphibian Assemblage
Long-toed salamander
Rough-skinned newt
Cascades frog
Pacific treefrog
Western toad
Objectives
1. Determine the extent and effects of Bd to
the N. CA montane amphibian assemblage
2. Determine if the effects of Bd depend on
climatic variables
3. Assess the potential for skin microbes to
confer resistance to Bd
4. Determine if temperature or pesticides
interfere with the skin microbes
Cascades frog (Rana cascadae)
•
•
•
•
•
Declining
Related to MYLF
All life stages highly aquatic
Susceptible to Bd in the lab
Relatively common in the
Klamaths
Range in California
(Vindum 1998)
Methods
• Landscape survey
• Population study
– Lassen (4 pop.s)
– Trinity Alps (9 pop.s)
• qPCR for Bd
• Lab trials - Skin microbes
– Characterization
– Anti-Bd assays
– Biofilm assays
• Temperature
• Contaminants
Results
•Bd present across
the landscape
•No spatial pattern
Results
•Cascades frogs
persist with Bd
•Some populations
appear to be
affected more
than others
Results
P = 0.09
Results
0.7
0.6
% Bd
0.5
0.4
0.3
0.2
0.1
0
150
170
190
210
day
230
250
Results
• Population dynamics
– 11 of 13 populations are small, have poor
recruitment
– Lack of subadult frogs
– Range in annual survival
Results
Adult
Subadult
Conclusions
•
•
•
•
Bd is widespread
Cascades frogs are affected but no current mass
die-offs
Temperature trend – cooler sites predicted to have
higher Bd prevalence
Young frogs are most susceptible
Implications
• Warming climate good for disease resistance?
– Many unknowns
– Variability
• Other climate influenced stressors
– Drought/hydroperiod
– Introduced fish
What’s Next?
• Why some populations and
not others?
– Track loads on individuals
• Why subadults and not
adults?
• How do innate skin defenses
respond to temperature
changes?
• Model disease dynamics with
climate change predictions.
Acknowledgements
Janet Foley
Sharon Lawler
Colleen Kamoroff
Monty Larson
Jen Brown
Hart Welsh Jr.,
Sherilyn Munger,
Cathy Johnson
Justin Garwood
Melanie McFarland