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

Abstract

Andean Toads of the genus Osornophryne are suspected to have direct development on the basis of clutch and egg features. In this work, we describe the morphology of Osornophryne occidentalis embryos from a nest collected in the field. Several traits are similar to those reported in brachycephaloid Eleutherodactylus coqui and other direct‐developing lineages. These include the pattern of formation of the body wall and the absence of oral and buccopharyngeal structures. Other features indicate the retention of ancestral larval characters. The development of forelimbs occurs in part within the operculum as in species with biphasic ontogeny; this has been reported in other direct‐developing species, and is similar to what is described in African viviparous bufonids. This salient feature, along with the long, low‐finned tail and the long and folded intestine early differentiated, gives these embryos a rather tadpole‐like appearance. Our data confirm that development in O. occidentalis occurs within terrestrial eggs until advanced stages, and this would satisfy current definitions of direct development. At the same time, morphological differences regarding other species with comparable breeding reinforce interpretations about the wide anatomical and ontogenetic variations associated with endotrophic nutrition.

Harlequin frog tadpoles—comparative buccopharyngeal morphology in the gastromyzophorous tadpoles of the genus Atelopus (Amphibia, Anura, Bufonidae), with discussion on the phylogenetic and evolutionary implication of characters

“…Lack of pustulations and papillae in the buccal floor and roof is not common in anurans and often associated with endotrophic development (Wassersug and Duellman 1984 ; Romero-Carvajal et al 2023 ). Nevertheless, feeding tadpoles may also present a reduction or lack these features, as in the case of oophagous (e.g., Vera Candioti et al 2021 ) and macrophagous (e.g., Dias et al 2019b , 2023 ) tadpoles.…”

“…Lingual papillae are also present in most anuran larvae, with some few exceptions (e.g., micohylids and several Dendropsophini; Vera Candioti 2007 ; Dias et al 2023 ). All Atelopus lack lingual papillae, as well as the endotrophic larvae of Frostius (Dubeux et al 2023 ) and the direct developer Osornophryne (Romero-Carvajal et al 2023 ). The optimization of this character state is ambiguous, but it is interesting noting that absence of it in Frostius and in Osornophryne is probably related to endotrophic development, while Atelopus retained a plesiomorphic state or lost those papillae independently is an interesting evo-devo question.…”

Egg burying behaviour in Pristimantis highlights the link between direct development and specialised parental care

“…This reproductive mode has evolved several times independently across different anuran, urodelan and gymnophionan lineages (Callery et al., 2001; Furness et al., 2022; Gomez‐Mestre et al., 2012; Liedtke et al., 2022). In Neotropical anurans, it is found in several species across the families Strabomantidae, Eleutherodactylidae, Craugastoridae, Bufonidae, Brachycephalidae and Hemiphractidae (Callery et al., 2001; Castroviejo‐Fisher et al., 2015; Liedtke et al., 2022; Romero‐Carvajal et al., 2023; Townsend & Stewart, 1985). Direct development is considered the most extreme adaptation to terrestrial life in amphibians, as it allows species to become completely independent from water bodies for reproduction (Gomez‐Mestre et al., 2012; Wells, 2007).…”