Transcript HHMI 2010 - Oregon State University

HHMI 2010
Impact of
Batrachochytrium dendrobatidis
on food web dynamics and its
consequences for larval amphibians
Katharina Scholz ([email protected])
Julia Buck
Andrew Blaustein
Global Amphibian Decline
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Some estimates show that amphibians are declining
more rapidly than either birds or mammals
Nearly 40% listed as globally threatened or
endangered (Stuart et al. 2004)
Climate change, contaminants, habitat loss, invasive
species, but also wildlife diseases like
chytridiomycosis
© USDA-ARS
Batrachochytrium dendrobatidis
hereafter Bd
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Chytrid fungus
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Infects keratinized tissues
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Reproduces via motile zoospores
© Joyce Longcore
Berger et al. (1999)
Batrachochytrium dendrobatidis
hereafter Bd
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
Estimated to be the greatest infectious disease
threat to biodiversity
Mortality rate of 90-100% in some amphibian
species
(Kilpatrick et al. 2009)
© Joyce Longcore
© Vance Vredenburg
Rana cascadae

Tadpoles have keratinized mouthparts
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Usually graze on periphyton
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Shown for other species: Graze less efficiently if
infected with Bd
(Venesky et al. 2010)
Parasites as Prey
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An alternative approach to study food webs:
include parasites as prey
Usually very abundant, reproduce fast
Zoospores of Bd are about the same size as
flagellates grazed by zooplankton
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Bd = food source for zooplankton?
A simple foodweb
?
Tadpoles
Zooplankton
?
Periphyton
Phytoplankton
Bd
Resources
© Joyce Longcore
Two hypotheses
+
Tadpoles
Zooplankton
+
Periphyton
Phytoplankton
Bd
•Bd zoospores beneficial for zooplankton
Resources
•Indirect positive effect on tadpoles
Two hypotheses
Tadpoles
Zooplankton
Periphyton
Phytoplankton
Resources
Bd
•No interaction between Bd and
zooplankton
•Bd infects tadpoles
•Tadpoles graze less efficiently
The Experiment
2 x 2 x 2 factorial experiment:
Tads Zoops Bd
Tads Zoops Bd
- / - / -
+ / - / -
- / - / +
+ / + / -
- / + / -
+ / - / +
- / + / +
+ / + / +
The Experiment
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8 treatments, 6 replicates
48 polyethylene
tanks at OSU's Lewis-Brown Horticulture
Research Farm
Response variables: amphibians
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Survival to metamorphosis
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Larval period length
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Mass at metamorphosis
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Snout-Vent Length (SVL) at metamorphosis
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Infection level
(via qPCR)
Response variables: community
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Weekly collect data on community
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Chlorophyll concentration
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Periphyton mass
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Quantify and identify zooplankton
Results
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Data collected for ten weeks
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75.2% metamorphs, 92.5% survival
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Analysed data using S-Plus
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ANOVA = Analysis of Variance Model
Results: Amphibians
Treatment Survival Days to
Mass
SVL
meta[mg/day] [μm/day]
morphosis
Zoops
+
Ø
Ø
Ø
Bd
Ø
Ø
Ø
Ø
Zoops*Bd
Ø
+
Ø
-
• Zooplankton increase larval period length
• Zooplankton*Bd increase larval period length and
decrease daily growth rate (SVL)
Results: Community
Tadpoles
Periphyton Phytoplankton Zooplankton
Ø
-
-
Zooplankton
Ø
-
N/A
Bd
Ø
Ø
Ø
•
•
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Tadpoles significantly decrease amount of
periphyton
Zooplankton significantly reduce amount of
phytoplankton
No effects of Bd were observed
Conclusion
Competition?
Tadpoles
Zooplankton
?
Periphyton
Phytoplankton
Resources
Bd
Conclusion
•Further research necessary to learn more about infectious
diseases like chytridiomycosis
•First step in studying interaction between Bd and other
organisms in aquatic communities
Acknowledgement
Funding
•Howard Hughes Medical Institute
(HHMI)
•Dr Kevin Ahern
•National Science Foundation (NSF)
•Zoology Research Fund (ZoRF)
•Society of Wetland Scientists (SWS)
Equipment/protocol
•Erin Scheessele
•PISCO laboratory
•Hacker laboratory
•Spatafora laboratory
•Tanguay laboratory
Field station
•Scott Robbins
•Don Hinds-Cook
Field assistance
•Mathew James
•Sahnzi Moyers
•Lindsay Biga
•Phyllis Buck
References
•Stuart, S.N, J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L.
Fischman, R.W. Waller. 2004. Status and trends of amphibian declines
and extinctions worldwide. Science 306: 1783-1786.
•Kilpatrick, A.M., C.J. Briggs, P.Daszak. 2009. The ecology and impact of
chytridiomycosis: an emerging disease of amphibians. Trends in Ecology
and Evolution 25: 109-118.
•Venesky, M.D., M.J. Parris, A. Storfer. 2010. Impacts of Batrachochytrium
dendrobatidis infection on tadpole foraging performance. EcoHealth in
press.
•Berger L, Speare R, Kent A. Diagnosis of chytridiomycosis in amphibians
by histologic examination. World Wide Web file,
http://www.jcu.edu.au/school/phtm/PHTM/frogs/histo/chhisto.htm, 20
November 1999