Make love the Bombay night frog way.
Male Bombay night frog. Image: SD Biju
It's time to update the amphibian version of the Kama Sutra, because a new form of "froggy style" has been pioneered by the Bombay night frog, a species endemic to the Western Ghats mountain range in India.
In research published Tuesday in PeerJ, a team led by amphibian expert and wildlife conservationist SD Biju of University of Delhi describe this previously unobserved lovemaking technique, which has been dubbed the "dorsal straddle."
It is the seventh known mode of "amplexus," an amphibian mating behavior that usually involves the male clutching the female's body and fertilizing her eggs as she lays them. For inquiring minds, here's a handy illustrated guide.
As you can see, frogs can get pretty creative when it comes to sex, especially those freaky deaky "independent" and "glued" couples. Indeed, according to the study's authors, frogs and toads display "the highest diversity in reproductive modes of all vertebrate taxa, with a variety of associated breeding behaviours."
Without further delay, here's the rundown on this newly anointed move in the frog sex playbook. After selecting her mate, the female "sits in front of him and creeps backwards until her abdomen is placed over his head, making physical contact," according to the paper. Sometimes, she needs to do this more than once before the male gets the message and mounts her. Instead of grasping her body, as is the norm for most amplexus modes, the male uses his hands to hold onto whatever branch or leaf is hosting this bout of frog romance, which normally hangs over a stream.
On average, the male stays mounted for about 13 minutes, during which time he releases semen onto the female's backside. The female signals when he should move with repeated dorsal arches, and soon after he dismounts, she lays her eggs in one bout, positioning them underneath her. Most frog species remain in an embrace during the fertilization, but in this case, the eggs are fertilized by the sperm running down the female's back and hind legs, reaching the eggs after the couple has separated.
The dorsal straddle is somewhat similar to the head straddle position, which has been observed in Mantellids, a family of frogs in Madagascar (Bombay night frogs, meanwhile, belong to the Nyctibatrachid family). In this case, the male bestrides the female's head and shoulders rather than the back, but the use of a "gravity assist," so to speak, is the same in both groups.
"Evolutionarily, Mantellids and Nyctibatrachids are not closely related," Biju told me via email. "Similar mating behaviour (not identical) may have evolved independently in both these groups of distinctly related frogs."
I asked him if the two families may have evolved the same behaviors due to environmental similarities, and he replied that he didn't there was a correlation "because several other ancient species of frogs are present within the same habitat as the Bombay night frogs but they differ considerably in their reproductive behaviours."
Short film about the study's results. Video: YouTube/frogindiadotorg
So why do these frogs opt for these loose straddles as opposed to the firmer, more traditional amplexus positions? Biju's team posited that a firmer grip on a branch, tree trunk, or leaf "might function to avoid falling and interrupting mating" though admittedly this doesn't work all the time.
"In at least half of the observations we made (nine observations), reproduction was interrupted by one or both of the frogs falling into the water," the team said. "Fallen individuals returned to the same position to continue the mating sequence, except when strong currents swept them away."
Breeding is hard enough without having to worry about falling into rapid waters, so it may be that Bombay night frogs evolved the dorsal straddle for better security. Incidentally, this species is also one of only 25 frogs in the world known to exhibit female mating calls as well as male calls, so they are unusual in more ways than one.
"The breeding behaviour of Nyctibatrachus humayuni [the Bombay night frog] has several unique elements: a new type of amplexus, the release of semen before oviposition, and the presence of a female call," the team noted, adding that "a good understanding of each species' ecology, including reproduction, is of major importance for planning and successfully implementing conservation strategies."
Indeed, Bombay night frogs are one of many anurans that are threatened by human activity, and are currently listed as "vulnerable" on the IUCN Red List of Threatened Species. It is imperative, then, that scientists like Biju and his team can continue studying the behavior and ecology of these inventive creatures so that informed conservation measures can be taken to protect them.
In other words, more studies of frogs caught in flagrante are in the works to ensure that successful mating—no matter the position—continues to go down.