Exceptional features of the embryonic ontogeny of a direct‐developing Robber frog

SALICA, M. J.; GOLDBERG, J.; AKMENTINS, M. S.; CANDIOTI, F. VERA

JOURNAL OF ZOOLOGY (1987)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2023

0952-8369

In frogs, the loss of the free-living tadpole stage implies deep transformations inmorphology and development, and the result is a combination of traits exclusive todirect development with the reduction or absence of typically larval features. Twotraits stand out in terraranans, a mostly Neotropical clade with ca. 1200 speciesknown or suspected to have direct development: (1) the development of forelimbs,which unlike in tadpoles and in several unrelated direct-developing lineages, in thisclade is described to occur completely exposed during ontogeny, and (2) the reductionof gills and their physiological replacement by highly vascularized tails for gasexchange. In this contribution, we report unusual aspects of the embryonic ontogenyin the Confused Robber frog Oreobates berdemenos, which complicate theinterpretation of morphological diversity in Terrarana and in direct-developing frogsin general. First, forelimbs develop initially entirely concealed by a larval operculum.Second, tail fins develop dorsal and ventral to the tail muscular core but theirarrangement changes to lateral during ontogeny. Third, the expansion of the tailfins appears to be a plastic character whose variation likely responds to individualconditions of humidity and/or oxygenation of each egg within the clutch. Finally,we report cells with the morphology of hatching gland cells in the rostral region ofembryos at stages about to hatch. If not vestigial, these cells could assist the eggtooth, which is characteristic of terraranans, with chemical softening of the eggcapsules during hatching.