Development of the retina is altered in the directly developing frog Eleutherodactylus coqui (Leptodactylidae)

The loss of a free-living larval stage during the evolution of directly developing frogs of the genus Eleutherodactylus resulted in dramatic alterations in ontogeny. Immunostaining for proliferating cell nuclear antigen reveals that in the directly developing frog Eleutherodactylus coqui pervasive cell proliferation occurs throughout the retina even after the plexiform layers have formed. In striking contrast to biphasically developing frogs (e.g. Discoglossus pictus or Xenopus laevis), in E. coqui proliferation becomes restricted to the ciliary margin only after the eye has reached the size typical of a postmetamorphic froglet and after its laminar structure has developed. As a consequence, the retina of E. coqui develops rapidly without recapitulating larva-typical stages. Our results suggest that dissociation of cell proliferation and differentiation can lead to the abbreviation of ontogenies during evolution.