Frog sex experts document amphibian’s seventh mating position

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This photo provided by researcher S.D. Biju shows Bombay night frogs in the newly discovered dorsal straddle during mating in a forest in the Maharashtra state of India. For years, scientists have thought that frogs and toads used only six positions to mate. In a paper published Tuesday, Biju of the University of Delhi and co-authors documented a seventh.

For years, scientists have thought frogs and toads used only six positions to mate. Now, in a forest in India, researchers say, they’ve documented a seventh.

This latest entry in the Kermit Sutra is called the dorsal straddle. Like other positions — but unlike mammal sex — it’s aimed at letting the male fertilize eggs outside the female’s body.

Researchers spent 40 nights in a dense forest, finding male Bombay night frogs by listening for their mating calls and filming the action when a female showed up.


In a paper released Tuesday by the journal PeerJ, S. D. Biju of the University of Delhi and co-authors report what they saw: Once the female makes physical contact, the male climbs onto her back. But instead of grasping her at the armpits or head, as frogs of other species do, he puts his hands on the leaf, branch or tree trunk the pair was sitting on. After an average of 13 minutes, she repeatedly arches her back, and he takes the hint and dismounts.

She lays her eggs after that and remains motionless, with her hind legs stretched around the clutch for several minutes. Then, she leaves.

The researchers suspect that during the straddle, he deposits sperm on her back. The sperm then trickles down to fertilize the eggs while she encloses them with her legs, the researchers suggest.

But a scientist unconnected to the work questions its conclusions. Narahari Gramapurohit of the Savitribai Phule Pune University in India, who studies the same frog species, said he doesn’t believe the report documents a new mating position. In an email, he also said he doubts the sperm is delivered to eggs from the female’s back.

In any case, all the frog work can come to naught. Of the 15 egg clutches the researchers monitored for the new paper, 12 were eaten by predators before hatching.

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