Mother Strawberry Poison Frogs Might Supplement Nutritive Eggs with Secretory Provisioning

Many animal lineages produce and provision offspring with nutritive material such as milk, lipid-enriched skin, or mucus. Some frogs deposit offspring into small pools of water known as phytotelmata, and a subset of those species also provision offspring with eggs. Often when parental frogs enter the water, oophagous tadpoles swim erratically, vibrate, nip, and even suck on adult skin, which has traditionally been interpreted as begging and tactile stimulus for oviposition. However, these behaviors are also consistent with the hypothesis that such mouth-to-skin contact serves the function of acquiring secretory provisioning from parents, as in the mucophagous fry of some fishes. Here we present images obtained with a macro lens at 6 K resolution of mother-offspring interactions in the strawberry poison frog, Oophaga pumilio, that suggest that tadpoles not only poke or nip maternal skin during feeding visits, but rather forcefully suck on it. We compare these observations to those from numerous lower resolution videos of previous experiments with O. pumilio, and place the findings in the context of a literature review of both anecdotal evidence of mother-tadpole interactions across phytotelm-breeding anurans and secretory provisioning across the animal kingdom. We propose that (1) skin sucking behavior may involve the transfer of nutritive mucous secretions or other defensive, immunological, hormonal, or microbial factors from mother frogs to tadpoles and that (2) such secretions may serve to supplement egg provisioning in this and other frogs with oophagous and phytotelm-dwelling larvae.