Author

Richard Elinson

Additional Author(s): Eugenia M. del Pino

Published on SDB CoRe: Feb 27 2012

Organisms: Vertebrates
Endoderm-derived: Digestive (Gut) Tract
Extraembryonic: Extraembryonic Tissues
Evolutionary Developmental Biology: Developmental Modifications
Organism: Frog (not Xenopus)
Stage of Development: Embryo

Object Description

Many frogs have eliminated the tadpole from their life history—a process termed direct development.  That evolution enables these frogs to reproduce on land; they never have to go into the water.  Direct developers, like this Eleutherodactylus coqui from Puerto Rico, form limbs and frog-like heads early (a, b).  They do not develop tadpole structures, except for the tail which has been co-opted for respiration (c).  Embryos develop in jelly capsules on land (d), where they are brooded by their father.  They become tiny frogs (e), which hatch from their capsules after three weeks.  The large eggs (3.5mm) have a lot of yolk to compensate for the lack of feeding as a tadpole.  The yolk remains attached to the intestine (f) for use in the first few days after hatching, a sequence similar to chickens. The last panel (f) is a digestive tract dissected from a newly hatched froglet.  The yolk is a large white (kidney-shaped) mass attached to the small intestine (tube-like structures extending from both ends).  Two lobes of liver (pink) and the gall bladder (green sphere) lie between the yolk and the stomach (mass off the anterior end of the intestine).  WIREs Dev Biol. 2011. DOI: 10.1002/wdev.23

References

Elinson, R., del Pino, E.M. Developmental diversity of amphibians. WIREs Dev Biol, 2011, Published Online: Dec 15 2011

Elinson, R. Direct development: an alternative way to make a frog. Genesis, 2001, 29:91-95.

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