HHMI 2010 Impact of Batrachochytrium dendrobatidis on food web dynamics and its consequences for larval amphibians Katharina Scholz (scholzk@onid.orst.edu) Julia Buck Andrew Blaustein 1

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

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

Batrachochytrium dendrobatidis hereafter Bd Estimated to be the greatest infectious disease threat to biodiversity Mortality rate of 90-100% in some amphibian species (Kilpatrick et al. 2009) © Vance Vredenburg © Joyce Longcore 4

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

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

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

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

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

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 - / - / - + / - / - - / - / + + / + / - - / + / - + / - / + - / + / + + / + / +

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

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

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

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

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)

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

Conclusion Competition? ? Tadpoles Zooplankton Periphyton Phytoplankton Bd Resources 17

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 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

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