- Researchers have rediscovered populations of tree frogs in several northern Indian states and China that were presumed extinct for 150 years.
- The frogs are unique enough to merit their own genus – the world’s 18th genus of tree frogs. They reproduce in water-filled tree hollows, with the tadpoles subsisting off unfertilized eggs.
- Like many of India’s amphibians, the newly rediscovered frogs are under heavy pressure from habitat loss.
An accidental discovery late one night in the forests of northeastern India has led to an entirely new genus of tree frogs, one that does some really strange things. The genus is described in a study published today in PLOS ONE.
The story starts in 1870, when a British naturalist collected two little frogs from the forests around Darjeeling, and took them back to the Natural History Museum of London. The scientific community named the species Polypedates jerdonii and never saw it again.
That is, until 2007.
A team of herpetologists led by renowned biologist Sathyabhama Das Biju of the University of Delhi was surveying a forest in the northeastern state of Nagaland one night. They were looking for ground-dwelling amphibians, but then they heard something that shifted their focus upward. As Biju told the Associated Press, “we heard a full musical orchestra coming from the tree tops. It was magical. Of course we had to investigate.”
The “orchestra” turned out to be tree frogs the scientists hadn’t seen before. They were eerily similar to P. jerdonii (which has been placed in several genera over the years): big, with bulging eyes, broad snouts, and lots of webbing between their toes.
Biju and his team spent the next few years collecting and examining these frogs from several northern Indian states and across the border in China, comparing their physical characteristics and their genes to known tree frog species. They also observed their behavior, and found out that these frogs laid their eggs in the hollows of trees, where water collected. But these hollows don’t contain enough food for developing tadpoles, so how did they survive?
The mystery was solved when the scientists took a closer look at the tadpoles’ stomachs. In them, they found the remains of eggs. The researchers surmise the female frogs, being unusually attentive mothers for amphibians, were returning to the hollows to lay unfertilized eggs for their offspring to eat.
Egg-eating – called “oophagy” – isn’t unique these Indian tree frogs. Various frog species engage in oophagy, one of the many resourceful adaptations amphibians have evolved to survive in oft-harsh environments. Some tadpoles, like those of the spadefoot toad, even eat each other. But the oophagy of these Indian tree frogs, along with distinctions in the tree frogs’ physical characteristics and genetic makeup, helped the researchers figure out that they were dealing with a completely new kind of frog. So unique, in fact, that it was given its own genus: Frankixalus. The scientists have so far identified two species in the genus: Frankixalus jerdonii, and an as-yet unnamed species.
mouthparts, which scientists think may help it suck up eggs. Photo by SD Biju.
jerdonii tadpole. The eyes are large and placed on the top of the head, unlike most other tadpoles that have eyes placed more towards the sides of their heads.
Unfertilized “nutritive” eggs found inside the dissected larval gut are
also visible in the ventral view. Photo by SD Biju.
With the addition of Frankixalus, the world now has 18 genera of tree frogs, eight of which were discovered in the last decade alone.
“Our discovery of this remarkable new genus of tree hole breeding frog from the relatively unexplored regions in Northeast India indicates that documentation of Indian amphibians is still incomplete,” Biju said. “It is also an indicator of how much work still remains to be done. This genus remained unnoticed by researchers probably because of its secretive life in tree holes.”
While the discovery of Frankixalus is a happy occasion for the herpetological community (one they celebrated with a charming video), danger looms for many of India’s frogs, including those of the new genus.
“Unfortunately many of our Indian amphibians face various extinction threats, especially due to habitat loss and fragmentation,” Biju said. “Several populations of the new genus were found in highly disturbed habitats, which is a reason for concern. The major threat to amphibians in India is massive habitat loss. Taking any conservation effort for amphibians will indirectly conserve several other life forms of that area.”
Indeed, Biju and his coauthors write in their study that several of the locations where they collected Frankixalus individuals have been compromised by destructive human activities like slash-and-burn agriculture. The forest monitoring platform Global Forest Watch shows ongoing tree cover loss in the region.
shows the collection site, its forest recently cleared by slash
and burn cultivation. Photo by SD Biju.
The researchers caution that with their specialized, tree-dependent reproduction strategy, Frankixalus frogs are particularly at risk from forest loss and degradation.
“This frog is facing extreme stress in these areas, and could be pushed to extinction simply from habitat loss,” Biju told the Associated Press. “We’re lucky in a way to have found it before that happens, but we’re all worried.”
Citation:
- Biju SD, Senevirathne G, Garg S, Mahony S, Kamei RG, Thomas A, et al. (2016) Frankixalus, a New Rhacophorid Genus of Tree Hole Breeding Frogs with Oophagous Tadpoles. PLoS ONE 11(1): e0145727. doi:10.1371/journal.pone.0145727