Frog sex just got a whole lot kinkier.
All of the world's nearly 7,000 known frog species mate in one of six different positions: Most involve the male grabbing the female around the waist or under the armpits in a mating "hug" called amplexus.
This special embrace helps the male and female get close enough so that his sperm fertilizes as many of her eggs as possible. But it's still pretty tame.
The Bombay night frog of India, however, hasn't gotten the memo—the amphibian mates in a never before seen position called the dorsal straddle.
Instead of releasing sperm near the female's cloaca, or all-purpose hole, the male Bombay night frog ejaculates on his partner’s back. The sperm then trickles down and fertilizes her eggs, according to a new study published June 14 in the journal PeerJ.
Not only that, they don't use amplexus at all—instead, the male presses his abdomen onto the female's back and holds onto a twig she's sitting on with his front toes.
A Bombay night frog couple demonstrates the dorsal straddle. [PHOTOGRAPH BY SD BIJU]
“So far, this mating position, is known only in Bombay night frogs," says study leader Sathyabhama Das Biju, a biologist at the University of Delhi.
"It has been a wonderful experience to observe the entire breeding sequence of this unique frog. It’s like watching a scripted event,” he said in an email.
University of Evansville herpetologist Noah Gordon calls the new discovery a very “nontraditional” mating position.
“It creates a new chapter in the frog Kama Sutra,” he says.
Das—whose nickname is "the frogman of India"—has spent several years observing the unusual behaviors of Bombay night frogs in the Western Ghats, a biologically rich mountain range that runs down the western side of India.
For example, females make mating calls and males fight over territory, he says—unique traits that inspired him to study these frogs’ mating habits.
It was no easy task, as the nocturnal amphibians are very secretive and mate only during monsoon season, when heavy rains and flooding make research a challenge.
But he persevered, and between 2010 and 2012, Das and colleagues watched and recorded mating Bombay night frogs using infrared light, which doesn't disturb them. Forty nights of data revealed the dorsal straddle, the newfound mating position.
To James Hanken, curator of herpetology at the Harvard Museum of Comparative Zoology, the dorsal straddle is unique—but not really all that different from what other frogs do.
It’s what happens next that he finds most interesting.
“Most of the time, the male releases his sperm as the female releases her eggs. In these frogs, the female doesn’t release her eggs until long after the male has left,” Hanken said. “That’s pretty surprising.”
Das and colleagues suggest the delay allows for the sperm to make its way down the female’s back to fertilize her eggs. Although Hanken believes that’s likely, he also points out that the researchers haven’t shown exactly when and where sperm meets egg.
“This is just one of many spectacular discoveries about amphibians in India," Hanken adds.
"They haven’t been well studied until recently, and with such biodiversity, there are bound to be more surprises."