1. Parasite Infection and Amphibian Limb Deformities
Cheyenne Conrad

2. Ribeiroia Trematode parasite Hermaphroditic
Distinctive esophageal diverticula
Indirect, complex life-cycle
3 known species
R. ondatrae in North America

5. Geographic Distribution
North & South America, Caribbean, Africa, (Australia?)
Parasites are found concentrated along bird migration paths

6. Ribeiroia causes limb deformities The Evidence
1999 study
Hypothesis: Ribeiroia is the cause of limb deformities in H. regilla (Pacific treefrogs)
Eggs collected for Eel river
Upon hatching, tadpoles exposed to one of six treatments:
0 cercariae
16 cercariae (light)
32 cercariae (intermediate)
48 cercariae (heavy)
80 Alaria cercariae
80 Alaria + 32 Ribeiroia

7. Ribeiroia causes limb deformities The Evidence

8. Limb Mutations

9. Ribeiroia causes limb deformities The Evidence
Results:
85% of frogs surviving to metamorphosis
suffered limb deformities.
Frequency of deformities increased with parasite density
Tadpole survivorship declined with increasing parasite density
Alaria penetrated tadpoles but caused no limb abnormalities nor increase in mortality
All abnormalities involved the hindlimbs

10. How does Ribeiroia cause limb mutations?
2 Hypotheses:
Mechanical vs. Chemical

11. How does Ribeiroia cause limb mutations?
Experimental implantation of resin beads into developing limb buds induce some malformations
lends support to mechanical hypothesis

12. How does Ribeiroia cause limb mutations?
Limb development in amphibians is dependent upon spatial organization of cells in the limb bud
Disruption of spatial organization in limb bud results in positional confrontations between cells
The result is duplicated and triplicated limbs, as well as other limb deformities

13. A new phenomenon?
Ribeiroia-induced malformations have occurred in North America since at least the 1940s
What factors are contributing the increased prevalence?

14. References
Johnson, P.T., K.B. Lunde, E.G. Ritchie, A.E. Launer The effect of trematode infection on amphibian limb development and survivorship. Science 284:
Johnson, P.T., D.R. Sutherland Amphibian deformities and Ribeirioa infection: an emerging helminthiasis. TRENDS in Parasitology 19:
Stopper, G.F., L. Hecker, R.A. Franssen, S.K. Sessions How trematodes cause limb deformities in amphibians. Journal of Experimental Zoology 294: