Developmental morphology of granular skin glands in pre-metamorphic egg-eating poison frogs
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Parents in many taxa, including insects, molluscs, 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 poison frogs sequester alkaloid-based defences from arthropod prey in granular skin glands. In at least one poison frog, Oophaga pumilio, mother frogs intermittently feed tadpoles until metamorphosis with nutritive eggs containing 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 determine whether their ontogenetic alkaloid profile coincides with granular gland development. Our findings suggest that alkaloid sequestration in tadpoles is delineated by the differentiation of rudimentary granular skin glands in epithelial 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.
KeywordsAlkaloid Ontogeny Poison gland Provisioning Tadpole
The authors thank Kim Hoke for equipment use and Alexandre-Benoit Roland for animal care. JLS is supported by an American Association for University Women American Postdoctoral Fellowship, and LAO is supported by a Bauer Fellowship from Harvard University, the L’Oreal Women in Science Fellowship, the William F. Milton fund from Harvard Medical School, a Konishi Research Grant from the International Society for Neuroethology, and the National Science Foundation (IOS-1528866).
JLS processed samples and wrote the manuscript. LAO acquired samples and edited the manuscript. Both designed the study.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the Institutional Animal Care and Use Committee of Harvard University (Protocol 12-10-01). This article does not contain any studies with human participants performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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