There is a proverb that says, "A frog cannot remember being a tadpole." It refers to someone who acts conceited from the start just because their circumstances have improved a bit. But there are frogs that cannot remember being tadpoles no matter how humble they try to be. That is because they skip the tadpole stage and are born looking just like adults.
A research team led by Professor Mark Scherz of the Natural History Museum at the University of Copenhagen in Denmark said on the 6th (local time) in the international journal "Vertebrate Zoology" that they "discovered three species of toads in Africa that skip the tadpole stage and give birth to live young." Toads, like frogs and narrow-mouthed toads, belong to the order Anura.
◇ Give birth to fully grown young to move to water
Textbooks teach that frogs and toads start from eggs, pass through the tadpole stage, and become adults with four legs. But three species belonging to the genus Nectophrynoides, toads that live in Tanzania, had no tadpole stage. These toads are commonly called "tree toads." Instead of laying eggs and hatching tadpoles in water, females carry their young inside the body and give birth to small toads with fully formed bodies.
The researchers explained that toads do not lay eggs because they give birth far from water. Only fully formed young can handle the journey back to the water.
Scherz said, "While frogs growing from tadpoles is known as a representative metamorphosis in biology, the nearly 8,000 species in the order Anura actually have a very diverse range of reproductive strategies."
In South America and Southeast Asia, there are also rare species like these toads that omit the tadpole stage. Hans Christoph Liedtke of the Spanish National Research Council (CSIC), a co-author of the paper, said, "Frogs or toads that brood eggs and then give birth to fully grown young account for less than 1% of the total."
◇ Compared with DNA from a 120-year-old specimen
Cases like tree toads giving birth to fully grown young were first discovered 120 years ago. German zoologist Gustav Tornier reported to the Royal Prussian Academy of Sciences in Berlin that he had first found a toad in Tanzania that gives birth to live young. The toad specimen Tornier first discovered is now housed at the Berlin Natural History Museum.
The researchers obtained DNA containing genes from the German toad specimen. Through this, they identified where the toads found in Tanzania belong. A natural history museum with only dead specimens helped reveal the identity of living wild animals.
The research team said the results not only shed new light on the evolutionary process of the order Anura but could also help conserve endangered species. The toad species discovered this time live in the Arc Mountains of eastern Tanzania, a treasure trove of biodiversity known for many species found nowhere else. But they are under threat from deforestation, mineral extraction, and climate change.
In fact, most tree toads are endangered. One species (Nectophrynoides asperginis) is already extinct in the wild, and another species (Nectophrynoides poyntoni) has not been observed again since it was first discovered in 2003.
References
Vertebrate Zoology (2025), DOI: https://doi.org/10.3897/vz.75.e167008