Researchers have just discovered the novel breeding strategy of a critically endangered (previously assumed extinct) frog: mating and laying eggs in live bamboo. Until now, no other frog has been known to do this. And these “direct developing” eggs hatch into tiny froglets—no tadpole stage here. The findings were published in the Biological Journal of the Linnean Society last month.
Frogs and toads have at least 40 known life strategies to increase their reproductive success: 17 occur in the water, and 23 are designed to take place on land. Now, a trio of researchers led by Kadaba Shamanna Seshadri from the National University of Singapore (NUS) has discovered the 41st reproductive mode while conducting field observations between 2009 and 2012 in south India’s Western Ghats.
In the wet evergreen forests of the Kalakad Mundanthurai Tiger Reserve, adult white-spotted bush frog (Raorchestes chalazodes) males look for narrow slits and openings made by insects in flute bamboo, Ochlandra travancorica. Adults can reach nearly 25 millimeters in length, and these holes are sometimes less than five millimeters long and three millimeters wide. Once he squeezes into the hollow stalks (called internodes), he’ll start vocalizing to attract a mate. When the female shows up, they mate, and she lays about five to eight eggs inside the live bamboo. The males stay in the bamboo nursery to take care of the egg clutch, leaving only for a few hours in the evening to feed, and then coming right back. And when they hatch, the babies emerge as fully-formed, but tiny, frogs.
This species, the researchers found, only breed in bamboo that have openings at the base of the internode. Those with openings at the top usually collect water—which could flood the eggs or drown the froglets. This bamboo-utilizing mode is the latest terrestrial breeding strategy to be recorded. “Frogs have shown the tendency of being increasingly non-aquatic," Seshadri tells BBC. These frogs "seem to have evolved this adaptation under certain pressures of natural selection."
The white-spotted bush frog was thought to be extinct for over a century, until it was rediscovered recently in this Indian reserve, a biodiversity hotspot that’s now listed as a UNESCO World Heritage Site. These bush frogs are only one of two species known to use this reproductive strategy: The Ochlandra reed frog (Raorchestes ochlandrae) breeds in the internodes of a different species of bamboo. Until this study, these reed frogs were thought to nest above ground or in trees—they’ve since been reclassified into this 41st mode.
“This is a significant discovery in two ways. First, it reiterates that natural history observations, often ignored, are fundamental for understanding evolutionary ecology,” study author David Bickford of NUS says in a news release. “Second, it sets a theoretical foundation to ask several interesting questions about the diversity of reproductive modes and the evolutionary pathways behind such amazing amphibian behaviors.”
