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Why Scientists Couldn’t Find this Tadpole for 125 Years

ByConor GearinNOVA NextNOVA Next

Indian dancing frogs become some of the showiest amphibians in the world when they grow up. Adult males get up on rocks and wag their legs to attract females. But researchers just discovered their tadpoles—and it turns out the young of this species hide from the limelight they later seek as adults.

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The whole family of dancing frogs had managed to keep their tadpoles well-hidden since the group was first discovered 125 years ago. In fact, it’s the only family out of the 54 frog and toad families for which scientists hadn’t seen tadpoles. It was a riddle that Sathyabhama Das Biju of Delhi University couldn’t ignore after he found 14 new species of dancing frogs in India’s Western Ghats mountain range in 2014.

Biju noticed a conspicuous absence of tadpoles in the streams where the adults live, but he did have one clue that would prove useful—the female frogs buried their eggs in the sandy streambed.

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When they returned to hunt for tadpoles, Biju and his team began digging in the streambed. In just an hour, they saw eight tadpoles wriggle away from them and burrow deeper into the sediment. Digging deeper, the biologists managed to catch 13 of them. The burrowing behavior means that the dancing frogs have fossorial tadpoles—a rare adaptation in which the young live underground.

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The burrowing tadpoles uncovered by Biju's team.

A look at the tadpoles’ guts showed that they weren’t just hiding in the sand—they ate it, too. The animals’ long, spiraling intestine was totally full of sand grains. It seems they’re able to get some nutrients from the grit.

Dancing frogs also turn out to be one of the few species that have ribs as tadpoles. The biologists think these bones might give them the structure needed to writhe like eels through the sand.

The odd tadpoles impressed other biologists. Here’s Richa Malhotra, reporting for the BBC:

“It is an interesting finding, predominantly because it was an entire family of frogs where we previously had very little indication of what the tadpoles were like,” says amphibian biologist Jodi Rowley of the Australian Museum Research Institute, who was not involved in the study.

“Members of at least five other families are known to have fossorial tadpoles, so it’s not unique among the frog world, but it is relatively rare,” she adds.

But this exciting discovery takes place against a grim backdrop: tropical amphibians are disappearing worldwide in a mass extinction. It’s linked to habitat loss and other human-driven causes, and it’s unclear if we can stop it. One of the Indian dancing frogs is listed as endangered , one is vulnerable , and another is becoming threatened due to clear-cut logging in the Western Ghats.

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An Indian dancing frog performing its mating display.

Even while amphibians are disappearing, there are still many frog and salamander species left to discover and better understand. Learning the fundamental facts about how tropical tadpoles use their habitats can help scientists better conserve them.

Watch a video from the researchers of the dancing frogs and their tadpoles below:

Photo credits: SD Biju

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