Three new toad species skip the tadpole phase and give birth to live toadlets

Most textbooks will tell you only one story of frog reproduction: Eggs to tadpoles to froglets to adults. But for three newly discovered species found in Tanzania this is not the case. The three new species of frogs belong to an unusual group of African toads in the genus Nectophrynoides — commonly called “Tree Toads.”

Instead of laying eggs that hatch into tadpoles, the female Tree Toads carry their offspring inside their bodies and give birth to fully formed, tiny toads. This makes them among the very few amphibians in the world capable of internal fertilization and true live birth.

“It’s common knowledge that frogs grow from tadpoles—it’s one of the classic metamorphosis paradigms in biology. But the nearly 8000 frog species actually have a wide variety of reproductive modes, many of which don’t closely resemble that famous story” says Assoc. Prof. Mark D. Scherz, Curator for Herpetology at the Natural History Museum Denmark, a coauthor on the study.

 Only a handful of frog species from South America and southeast Asia have developed similar strategies making these toads a rare case in the animal kingdom.

 “Live-bearing is exceptionally rare among frogs and toads, practiced by less than 1% of frogs species, making these new species exceptionally interesting,” says H. Christoph Liedtke a co-author from the Spanish National Research Council, who has specialized in the evolution of amphibian reproductive modes.

120-year-old frog DNA

Back in 1905, a German researcher, Gustav Tornier, presented to the Royal Prussian Academy of Sciences in Berlin, the discovery of a toad from Tanzania that, astonishingly, gives birth to live young. At the time, it was the only known species of frog in the world to do so.

The frogs originally found by Tornier are today housed at the Museum für Naturkunde in Berlin, and the research team were able to secure DNA from the original frogs using methods collectively known as ‘museomics’.

“Some of these specimens were collected over 120 years ago. Our museomics work was able to reveal exactly which populations those old specimens belonged to, giving us a lot more confidence for future work on these toads,” says Dr Alice Petzold of the University of Potsdam, who carried out the museomics portion of the study,

“Phylogenetic work from a few years ago had already let us know there was previously unrecognised diversity among these toads. But by travelling to different natural history museums and examining hundreds of preserved toads, I was able to get a better idea of their morphological diversity, so we could describe these new species,” says Christian Thrane from University of Copenhagen and first author on the study.