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

Abstract

In frogs, the loss of the free‐living tadpole stage implies deep transformations in morphology and development, and the result is a combination of traits exclusive to direct development with the reduction or absence of typically larval features. Two traits stand out in terraranans, a mostly Neotropical clade with ca. 1200 species known or suspected to have direct development: (1) the development of forelimbs, which unlike in tadpoles and in several unrelated direct‐developing lineages, in this clade is described to occur completely exposed during ontogeny, and (2) the reduction of gills and their physiological replacement by highly vascularized tails for gas exchange. In this contribution, we report unusual aspects of the embryonic ontogeny in the Confused Robber frog Oreobates berdemenos, which complicate the interpretation of morphological diversity in Terrarana and in direct‐developing frogs in general. First, forelimbs develop initially entirely concealed by a larval operculum. Second, tail fins develop dorsal and ventral to the tail muscular core but their arrangement changes to lateral during ontogeny. Third, the expansion of the tail fins appears to be a plastic character whose variation likely responds to individual conditions 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 of embryos at stages about to hatch. If not vestigial, these cells could assist the egg tooth, which is characteristic of terraranans, with chemical softening of the egg capsules during hatching.

Direct development or endotrophic tadpole? Morphological aspects of the early ontogeny of the plump toad Osornophryne occidentalis (Anura: Bufonidae)

“…In the well‐known terraranan E. coqui , an opercular fold differentiates in early embryos (about TS5‐6) and grows over the forelimbs, covering them in two‐thirds for only a few hours (Callery & Elinson, 2000). Although this is likely the case in other terraranans (i.e., short, transient opercular folds covering only the proximal part of the forelimbs are reported; e.g., Goldberg et al, 2020), recent observations in Oreobates berdemenos indicate that a complete larval operculum could develop in other species of this large clade (Salica et al, 2023).…”

Linking landscape and genetic variation in the heterogeneous Yungas Andean forest' hotspot: a multi taxa approach

“…Moreover, both anuran species are not only endemic but also habitat specialists, particularly in their reproductive behaviours (Goldberg et al, 2006;Salica et al, 2023) to be related to changes in vegetation resulting from past climatic fluctuations (Braun et al, 2005). Although these species have similar geographic distributions within the study area, T. cinderella exhibited a much more sensitive response to the environmental dissimilarity gradient.…”

“…Notably, two of the species exhibiting a significant influence of IBRsuit according to MMRR are anurans ( O. barituensis and M. rubriventris ), a pattern attributed to the intrinsic characteristics of this group‐ namely, thermal‐conformality, skin permeability and low vagility‐ rendering them more susceptible to environmental changes (Wake & Vredenburg, 2008). Moreover, both anuran species are not only endemic but also habitat specialists, particularly in their reproductive behaviours (Goldberg et al., 2006; Salica et al., 2023), emphasizing the direct role of environmental suitability in shaping their reproductive success. However, both species showed spatial autocorrelation, which could potentially inflate Type I error in analyses derived from Mantel test, such as MMRR.…”