1. HHMI 2010 Impact of Batrachochytrium dendrobatidis
on food web dynamics and its consequences for larval amphibians
Katharina Scholz
Julia Buck
Andrew Blaustein 1

2. Global Amphibian Decline
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 2

3. Batrachochytrium dendrobatidis
hereafter Bd
Chytrid fungus
Infects keratinized tissues
Reproduces via motile zoospores
Berger et al. (1999)
© Joyce Longcore 3

4. Batrachochytrium dendrobatidis
hereafter Bd
Estimated to be the greatest infectious disease threat to biodiversity
Mortality rate of % in some amphibian species
(Kilpatrick et al. 2009)
© Vance Vredenburg
© Joyce Longcore 4

5. Rana cascadae Tadpoles have keratinized mouthparts
Usually graze on periphyton
Shown for other species: Graze less efficiently if infected with Bd
(Venesky et al. 2010) 5

6. Parasites as Prey
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
Bd = food source for zooplankton? 6

7. A simple foodweb ? ? Tadpoles Zooplankton Periphyton Phytoplankton Bd
Resources
© Joyce Longcore 7

8. Two hypotheses + Tadpoles Zooplankton + Periphyton Phytoplankton Bd
Bd zoospores beneficial for zooplankton
Indirect positive effect on tadpoles
Resources 8

9. - Two hypotheses Tadpoles Zooplankton Periphyton Phytoplankton Bd
No interaction between Bd and zooplankton
Bd infects tadpoles
Tadpoles graze less efficiently
Resources 9

10. 2 x 2 x 2 factorial experiment: Tads Zoops Bd Tads Zoops Bd
The Experiment
2 x 2 x 2 factorial experiment: Tads Zoops Bd Tads Zoops Bd
- / - / -
+ / - / -
- / - / +
+ / + / -
- / + / -
+ / - / +
- / + / +
+ / + / +

11. The Experiment
8 treatments, 6 replicates 48 polyethylene tanks at OSU's Lewis-Brown Horticulture Research Farm 11

12. Response variables: amphibians
Survival to metamorphosis
Larval period length
Mass at metamorphosis
Snout-Vent Length (SVL) at metamorphosis
Infection level (via qPCR) 12

13. Response variables: community
Weekly collect data on community
Chlorophyll concentration
Periphyton mass
Quantify and identify zooplankton 13

14. Results Data collected for ten weeks 75.2% metamorphs, 92.5% survival
Analysed data using S-Plus
ANOVA = Analysis of Variance Model

15. Results: Amphibians Treatment Survival Days to meta- morphosis
Mass [mg/day]
SVL [μm/day]
Zoops Ø + Bd
Zoops*Bd -
Zooplankton increase larval period length
Zooplankton*Bd increase larval period length and decrease daily growth rate (SVL)

16. Results: Community - Periphyton Phytoplankton Zooplankton Tadpoles Ø
N/A Bd
Tadpoles significantly decrease amount of periphyton
Zooplankton significantly reduce amount of phytoplankton
No effects of Bd were observed

17. Conclusion Competition? ? Tadpoles Zooplankton Periphyton
Phytoplankton Bd
Resources 17

18. 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

19. Acknowledgement Field assistance Funding Mathew James
Sahnzi Moyers
Lindsay Biga
Phyllis Buck
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

20. References
Stuart, S.N, J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L. Fischman, R.W. Waller Status and trends of amphibian declines and extinctions worldwide. Science 306:
Kilpatrick, A.M., C.J. Briggs, P.Daszak The ecology and impact of chytridiomycosis: an emerging disease of amphibians. Trends in Ecology and Evolution 25:
Venesky, M.D., M.J. Parris, A. Storfer 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, 20 November 1999