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Weird and Wild! Unique Mating Position of Frogs Discovered

Jun 17, 2016 03:21 PM EDT
Mating Frog
The photo shows a male frog clasping onto a female frog while mating.
(Photo : Pixabay/aubrechtovamar/Creative Commons)

There are about 7,000 frog species in the planet and for years, scientists have thought that all these frogs use only six positions when mating. That was the case until researchers in India discovered the seventh position dubbed "glued."

Sathyabhama Das Biju of the University of Delhi and his co-authors spent 40 nights in the dense forest near Humbarli village, Koyna, Satara District, Maharashtra documenting the research. With the aid of a camera and infrared light, they were able to film the sexual behavior of Bombay night frogs.

The usual mating positions of the frogs involve a behavior called "amplexus" where male frogs clasp the female and juxtapose his side near the cloacae to deposit the sperm cells.

However, the new sexual position demonstrated by the Bombay frogs was different. During the "glued" position, scientifically known as the dorsal straddle, the male frog rides on the back of the female frogs and ejaculate on his partner's back, allowing the sperm cells to trickle down and fertilize the female's eggs. Moreover, the amplexus behavior is not used at all.

Instead of grabbing the female frog's head, shoulder or waist, the male frog holds onto a twig or branch where they are mating.

(A–E) Sequence of breeding behaviour in Nyctibatrachus humayuni; (F–G) Egg development.
(Photo : Peer J)
(A) Female approaches a calling male. (B) Female touches male just before the dorsal straddle (arrow indicates the position of female’s leg on male’s head). (C) Male mounts the female in a dorsal straddle, and most likely sperm is released on her back during this moment (arrow indicates the male’s hand positioned on the leaf, but not clasping the female). (D) Female deposits eggs and remains motionless with her hind legs stretched around the eggs. The male is mostly seen sitting close-by without any physical contact with the female. (E) After the female leaves the oviposition site, the male sits on or near the eggs and continues to call. (F) Freshly laid eggs, pigmented (egg diameter 3.5 ± 0.2 mm, n = 20). (G) Developing embryos on the 19th day, just before hatching out of the eggs.

As per the researchers' formal definition, dorsal straddle is a loose form of contact in which the male sits on the dorsum of the female prior to oviposition but without clasping her.

After being still in that position for about 13 minutes, the female frog will repeatedly arch its back and the male will unmount the female.

The nontraditional mating position has been observed so far in Bombay night frogs.

According to Amphibia Web, Bombay night frogs are short and stout. The head is broad, with a snout that is short and rounded. They are endemic to the Western Ghats mountains of the state of Maharashtra in southwestern India. At present, they are classified as vulnerable because of habitat loss and pollution of water bodies.

"So far, this mating position, is known only in Bombay night frogs," study leader Sathyabhama Das Biju told National Geographic in an e-mail interview

"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.

The paper detailing the discovery was published in the journal PeerJ. 

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