Zoologger: Only known 'potter' frog packs eggs in mud - via Herp Digest

• 17:05 27 May 2014 by Sandhya Sekar
• For similar stories, visit the Zoologger Topic Guide (New Scientist)

Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species: The kumbara night frog, Nyctibatrachus kumbara

Habitat: Stream and river beds in the forests of the Western Ghats of southern India

It's good to be different. If you're a new rock band there's no point sounding like Coldplay, because Coldplay has that sound sewn up and you won't be able to compete.

It's a similar situation in frog reproduction. A newly discovered species from southern India differentiates itself in part by being the only known amphibian to coat its eggs in mud. The mud may well protect the eggs, but that is probably not the whole explanation.

The new species, called the kumbara night frog (Nyctibatrachus kumbara) is one of several frog species crammed together into a small area. That means it pays them to be as different as possible. Indeed, they are a different size to their neighbouring species, they mate differently – and they smear mud all over their developing offspring.

Frog lovers

The frogs were discovered by Kotambylu Vasudeva Gururaja of the Indian Institute of Science in Bangalore and his colleagues, during a series of expeditions between 2006 and 2012. The kumbara night frog has only been found in swamp forests in the Karnataka region of the Western Ghats, where nutmeg trees form a dense canopy.

"Kumbara" means "potter" in Kannada, a local language. "The male frog shows such finesse when it applies mud to the eggs," says Gururaja.

At dusk, male kumbara night frogs attract females with a distinctive "tok" call. If a female wishes to mate with him, the two stand on their hind legs to do so. Afterwards, the female rotates into a handstand, and lays about five pigmented eggs on to a twig or some other flora.

The male then moves toward the egg clutch, stands on his hind limbs, collects mud from the stream bed with its forelimbs and spreads it on the eggs (see picture, above right). He repeats this about 15 times, covering all the eggs with mud.

Mud, glorious mud

This is the first time such behaviour has been observed in amphibians. "I have never heard of or observed mud packing in any amphibian," says Sathyabhama Das Biju at the University of Delhi in India, who was not involved with the study.

There are some straightforward explanations. "Since the eggs are laid about 6 centimetres above the water, there is a chance they can go dry," says Gururaja. "The mud pack could be preventing that. It could also be a camouflage against egg predators like crabs, insects and snakes."

But more fundamentally, Gururaja thinks the frogs just need to be different from their neighbours. Two closely related species, Jog's night frog and Rao's dwarf wrinkled frog, live in the same area. Gururaja found that the three species differ in many ways; they are different sizes, make different calls, mate differently and care for their young differently.

Biologists call this "reproductive character displacement". Closely related species that live in the same place must differentiate themselves with distinct behaviours to avoid futile interbreeding. If they live far apart, they can afford to behave more similarly.

Journal reference: Zootaxa, DOI: 10.11646/zootaxa.3796.1.2