There’s not really a good time to bring up amphibian mating habits at the dinner table. I figured that I was probably safe given that I was surrounded by scientists, but, all the same, I tried to make sure that no one was raising a fork to their mouths when I blurted out “You guys! There are frogs that have sex!”
The inspiration for my outburst came from a PLOS One paper published just before I headed out the door for New Year’s Eve dinner. In it, biologists Djoko Iskandar, Ben Evans, and Jimmy McGuire describe a frog that reproduces unlike any other known species.
Most frogs and toads look like they’re having sex when they’re mating, but this is a superficial illusion. It’s a behavior called amplexus in which the male amphibian clasps the female around the torso, shoulders, or head and releases his sperm as she lays her eggs.
The new frog species – named Limnonectes larvaepartus – is one of the rare exceptions. Like a handful of other frogs and toads, this newly-described amphibian from Sulawesi Island is capable of internal fertilization. The way the frogs accomplish this is a mystery – the Limnonectes larvaepartus males appear to lack what science has politely called an “intromittent organ” – but what happens next is a sure sign that the fanged frogs don’t spawn like other species.
All other frogs and toad species that have sex deliver their young in one of two ways. The females either lay their internally-fertilized eggs in typical amphibian fashion or the mothers give birth to well-developed froglets. Limnonectes larvaepartus splits the difference. Females of the new species, Iskandar and colleagues report, gives live birth to tadpoles.
The researchers first discovered this unusual ability while prepping collected frogs. When they dissected some of the females, “the abdominal wall was observed to quiver, and incision resulted in living tadpoles emerging from the opening.” Live frogs later gave birth to squiggly tadpoles at the time of collection and while being held for study.
While there’s a possibility that the fanged frogs may have been capable of retaining those tadpoles until they fully metamorphosed into froglets, Iskandar and coauthors consider this unlikely. All 19 pregnant females collected for the study had tadpoles inside, not froglets, and the researchers also found free-living tadpoles in streamside pools. Once released into the outside world, the developing frogs live off what little yolk they have left before starting to feed for themselves. And given that this news was received positively as dinner concluded, I can heartily recommend that you share the tale of this remarkable frog the next time you meet friends for a meal. I’m sure they’ll find it ribbiting.
Iskandar, D., Evans, B., McGuire, J. 2014. A novel reproductive mode in frogs: A new species of fanged frog with internal fertilization and birth of tadpoles. PLOS One. 9 (12): e115884. doi:10.1371/journal.pone.0115884