Developmental morphology of granular skin glands in pre-metamorphic egg-eating poison frogs

Abstract

Parents in many taxa, including insects, mol- luscs, fish, snakes, and amphibians provision chemical defences, such as peptides, steroids, or alkaloids to their offspring to reduce the risk of predation. In most cases, those defences are transferred to offspring in the egg and gradually diminish throughout the larval period. Adult poi- son frogs sequester alkaloid-based defences from arthro- pod prey in granular skin glands. In at least one poison frog, Oophaga pumilio, mother frogs intermittently feed tadpoles until metamorphosis with nutritive eggs contain- ing those alkaloid-based defences. However, alkaloids are not detected in tadpoles until they reach the middle stages of larval development. Here, we investigate the histology of a developmental series of O. pumilio tadpoles to deter- mine whether their ontogenetic alkaloid profile coincides with granular gland development. Our findings suggest that alkaloid sequestration in tadpoles is delineated by the dif- ferentiation of rudimentary granular skin glands in epithe- lial tissue. The timing of differentiation of granular glands in this species coincides with other anurans. Thus, provisioning of chemical defences to offspring is likely constrained by developmental timing of derived structures that can effectively store those toxic or noxious compounds.