Collaborative Resources for
Learning Developmental Biology
Collaborative Resources for Learning Developmental Biology
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Pacific Chorus Frog Limb Deformity
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Stanley Sessions

Published on SDB CoRe: Feb 22 2012

Organisms: Vertebrates
Mesoderm-derived: Limb Formation; Skeleton
Teratogens: Pathogens
Ecological Developmental Biology: Teratogens
Organism: Frog (not Xenopus)
Stage of Development: Adult

Object Description

This Pacific Chorus Frog (Pseudacris regilla) from a California pond was the victim of an attack by the infecting stage of a parasitic flatworm (Trematode, species Ribeiroia ondatrae).  It is an example of how environmental factors can control development.  The limb deformities (shown by Alcian blue/Alizarin red staining) appear to be caused by the trematode cyst physically disturbing the positional relationships of cells within the developing limb bud.  In other words, the cysts actually split the limb buds in multiple places creating extra limbs.

The parasitic infection of the frog is part of an adaptive parasite host-modification. The frogs serve as second intermediate hosts in a complex trematode life cycle involving aquatic fowl (e.g. heron) as the primary hosts/carriers of the adult worms, and pond snails as the first intermediate hosts (in which the trematodes develop into the infectious cercariae (larvae)).  The parasite "handicaps" the frogs, knocking out their main means of escaping from predators, which increases the chance of the frog being captured and eaten by the primary host and the parasite thus completing its life cycle.


Stopper, G., L. Hecker, R.A. Franssen, Sessions, S.K. How trematodes cause deformities in amphibians. Journal of Experimental Zoology (Mol Dev Evol), 2002, 294:252-263.

Sessions, S.K., R.A. Franssen, Horner, V.L. Morphological Clues from Multilegged Frogs:  Are Retinoids to Blame?  Science, 1999, 284:800-802.

Hanken, J., Wassersug, R.J. The visible skeleton. Funct Photog, 1981, 16:22-26.

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