A unique frog species has been discovered that mats and lays eggs upside down. The Charles Darwin frogs, named after the renowned naturalist, position themselves upside down on the walls of tree cavities, entirely out of water. The hatchlings then drop into the water below and develop as free-swimming tadpoles.
Remarkable Behavior
“This is remarkable. Upside-down spawning is the most unique behavior in this frog. No other frog is known to lay eggs on inner walls of tree holes in an upside-down posture with bodies completely outside water,” says SD Biju of the University of Delhi and a fellow at the Harvard Radcliffe Institute. This discovery is crucial for understanding how this species interacts with its environments and which habitats are essential for survival.
Extensive Study and Research
A team of biologists from the University of Delhi, the Zoological Survey of India, Harvard University, and the University of Minnesota studied these frogs’ reproductive behavior. Over three years, they camped for 55 nights during the monsoon rains to observe the secretive Charles Darwin frogs.
Unique Mating Calls
The uniqueness of this species extends to its mating calls. Unlike most frogs, which produce simple, single-type calls, Charles Darwin frogs produce three “complex” calls. During mating, aggressive males engage in physical fights, using their limbs to kick and box and even biting off body parts or entire heads.
Aggressive Encounters
Researchers noted that despite the aggression, these fights rarely result in death. These confrontations occur in small tree cavities filled with rainwater, unlike larger open-water bodies where other species fight. This aggressive behavior and the unique upside-down mating strategy prevent bachelor males from disrupting egg-laying.
Conservation Concerns
The Charles Darwin frog is endemic to a few islands in the Andaman archipelago. The species breeds in natural and artificial sites, such as watered plastic sapling bags and discarded containers.
Habitat and Breeding Challenges
“The frogs’ use of trash for breeding is both surprising and worrying,” says Sonali Garg, a fellow at Harvard University who co-led the study. Habitat loss and competition for limited resources may drive these frogs to unnatural breeding sites. Researchers emphasize the need to protect natural breeding sites critical for the species’ survival.
Broader Implications
“This find is an example of the remarkable diversity of amphibians and reproductive behaviors that are still unknown to science, especially from unexplored regions in biodiversity hotspots of tropical Asia,” says James Hanken of Harvard University. The study highlights the importance of understanding and preserving the unique behaviors and habitats of vulnerable species like the Charles Darwin frog.
