An unexpected tadpole: developmental mode and larval morphology of endotrophic Rhinella justinianoi (Anura: Bufonidae), with implications for bufonid larval ecomorphology and evolution

Abstract

Among bufonids, Rhinella stands out for its high diversity in larval morphology and ecomorphology, including forinstance proverbial pond-type tadpoles (e.g., the R. marina group), generalized tadpoles from lotic systems (e.g.,in the R. spinulosa group), and tadpoles that develop in phytotelmata (e.g., some species within theR. margaritifera group). The R. veraguensis group comprises highly specialized tadpoles with the abdominal wallmodified into a sucker (R. chrysophora, R. quechua, and R. veraguensis), as well as forms that exhibit gular bulgeslikely representing an intermediate state toward the presence of an abdominal sucker (R. rumbolli). Given thegenerally conservative larval morphotypes within species groups in this and other bufonid genera, the discoveryof tadpoles of R. justinianoi from a captive breeding population was surprising. Contrary to expectations, these areendotrophic nidicolous tadpoles that combine features typical of this developmental mode (e.g., mouthparts lessdeveloped than in related lotic tadpoles, large otic capsules) with traits characteristic of the R. veraguensis group(e.g., gular bulges, labial tooth row A2 not interrupted). In this work, we describe the external and skeletalanatomy of a small sample of tadpoles and discuss their relevance in the context of phylogeny, developmentalmodes, and larval ecomorphology in Rhinella. In addition, we briefly summarize the taxonomic distribution andmorphological evolution of endotrophic larvae in Bufonidae.