Transcript cheyenne.ppt

Parasite
Infection and
Amphibian Limb
Deformities
Cheyenne Conrad
Ribeiroia
 Trematode
parasite
 Hermaphroditic
 Distinctive esophageal diverticula
 Indirect, complex life-cycle
 3 known species
R. ondatrae in North America
Geographic Distribution
 North
& South
America, Caribbean,
Africa, (Australia?)
 Parasites
are found
concentrated along
bird migration paths
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
Ribeiroia causes limb deformities
The Evidence
Limb Mutations
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
How does Ribeiroia cause limb mutations?
2
Hypotheses:
Mechanical vs. Chemical
How does Ribeiroia cause limb mutations?
 Experimental
implantation of resin beads
into developing limb buds induce some
malformations
 lends support to mechanical hypothesis
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
A new phenomenon?
 Ribeiroia-induced
malformations have
occurred in North America since at least
the 1940s
 What
factors are contributing the
increased prevalence?
References

Johnson, P.T., K.B. Lunde, E.G. Ritchie, A.E. Launer.
1999. The effect of trematode infection on
amphibian limb development and survivorship.
Science 284: 802-804.

Johnson, P.T., D.R. Sutherland. 2003. Amphibian
deformities and Ribeirioa infection: an emerging
helminthiasis. TRENDS in Parasitology 19: 332-335.

Stopper, G.F., L. Hecker, R.A. Franssen, S.K. Sessions.
2002. How trematodes cause limb deformities in
amphibians. Journal of Experimental Zoology 294:
252-263.