Development of the adult-like larval stomach of Lepidobatrachus laevis

Abstract

Most frogs diets shift between the larval and adult phases, from a filter-feeding herbivore to a bulk-feeding carnivore. This change in diet corresponds to a biphasic mode of gut development that begins during embryogenesis and resumes at metamorphosis, when nearly the entire anatomy of the tadpole is reorganized into its adult morphology. The frog Lepidobatrachus laevis forgoes this metamorphic shift in feeding mode and instead consumes a bulk-feeding, carnivorous diet both as a larvae and as an adult. This unusual larval diet is enabled by the presence of an adult-like stomach in the tadpole. This study investigates the anatomy and embryonic development of the larval stomach of L. laevis and what, if any, further changes occur during metamorphosis. The histology of embryonic and metamorphic stomach development is compared to that of Xenopus tropicalis, a frog with a typical larval stomach. We find that L. laevis directly forms an adult-like stomach during embryonic development without first forming a larval-like configuration. Moreover, no additional major remodeling of the stomach occurs during metamorphosis, although the stomach does gradually and slightly increase in complexity, proliferating more glands and increasing connective tissue and muscle layers, between hatching and the end of metamorphosis. This developmental trajectory of the stomach in L. laevis corresponds with the megalophagous, carnivorous diet these frogs maintain from tadpole to adult, as well as the maintenance of active feeding throughout metamorphosis. These results will facilitate future investigations into the mechanisms underlying the evolution of this unusual larval anuran feeding strategy, as well as the broader study of how development mediates evolutionary change.