TWIL #072 - Some Frogs Dissolve Their Own Tadpoles to Lay More Eggs
The strawberry poison dart frog lays unfertilised 'trophic eggs' specifically to feed its tadpoles. But if conditions turn unfavourable, some frog species will absorb their clutch of eggs back into their body entirely.
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- #biology
- #nature
Frogs have some of the most diverse and unusual parental strategies of any vertebrate group. Two in particular stand out:
Trophic eggs: The strawberry poison dart frog (Oophaga pumilio) of Central America lays clutches of eggs that hatch into tadpoles. The father then carries the tadpoles individually on his back to small pools of water in bromeliads - plant cups that hold a few millilitres of rainwater. The mother then visits each pool and lays additional, unfertilised eggs directly into the water as food for the tadpole. These "trophic eggs" are produced specifically as nutrition, not for reproduction, and the mother adjusts her production based on the tadpole's nutritional needs. Each tadpole is provisioned individually.
Egg absorption (oocyte resorption): When environmental conditions deteriorate - a drought, a predator presence, or nutritional shortage - various frog species can reabsorb their own eggs before or after fertilisation. The eggs are broken down and their nutrients recycled back into the female's body. This is not unique to frogs, but the speed and completeness of the process in some anuran species is notable. The female essentially dissolves the clutch to reclaim the energy investment and try again under better conditions.
Darwin's frog (Rhinoderma darwinii, native to Chile and Argentina) has an even more striking arrangement: the male swallows fertilised eggs into his vocal sac (not his stomach), where they develop through the tadpole stage. After 50–70 days, fully metamorphosed froglets emerge from his mouth.
The male pregnancy equivalent: In Surinam toads (Pipa pipa), fertilised eggs are pressed into the spongy skin of the female's back by the male during an elaborate aquatic mating cartwheel. The eggs become embedded, grow within their own pockets in her skin, and emerge as fully-formed toadlets weeks later directly through her back.