An Indo-American team of researchers led by Malayali scientist S D Biju, known as the Frogman of India, has discovered a unique breeding behaviour in a frog species endemic to the Andaman Islands. The discovery on the frog ‘Andamanese Charles Darwin’s Frog’ -- currently listed as ‘vulnerable’ in the International Union for Conservation of Nature (IUCN) red list -- also serves to highlight the fact that this unique amphibian is facing a loss of breeding sites. Further, the study warns that the species may not be able to survive amid a competition for limited resources and in the face of increasing human dominance. The study was carried out by a team of biologists from the University of Delhi, Zoological Survey of India, Harvard University and the University of Minnesota, with the report set to be published in the July 2024 issue of Breviora. The Charles Darwin’s frog belongs to a large radiation of Asian frogs that comprises 220 species. What makes the frog breed unique is that they deposit terrestrial eggs above the water surface and the posture of the mating pair at the time of egg-laying. The pair places themselves in a vertical, upside-down posture on tree cavity walls with their bodies completely out of the water. “Upside-down spawning is the most remarkable behaviour in this frog,” Biju said. He is currently a fellow at the Harvard Radcliffe Institute and an associate of the Harvard’s Museum of Comparative Zoology. “No other frog is known to lay terrestrial eggs inside tree holes in an upside down position. This discovery is fundamental in understanding how the species interacts with its environments and which habitats are essential for its survival,” he said. The researchers were amazed by the mating techniques used and the fights among male frogs for female frogs. They had to spend 55 nights during the monsoon season to study the secretive reproductive behaviour of these frogs. The male produces three different types of sounds to attract the female, Biju said. “Among these, the aggressive calls are also unique. This is to ward off the competing males. However, if the aggressiveness fails, they indulge in physical combat like humans. These include kicking and boxing using their hands and legs. They also bite their adversaries’ body parts or even the entire head to win and mate with the female. However, even after being unsuccessful in getting a pair, the opponent would try to insert their heads between the bodies of the pair to seperate them. To avoid intruders, the female frog climbs the wall of the tree hole with the male on her back,” he said. According to the scientist, the upside-down spawning behaviour has evolved as a means of preventing aggressive unpaired males from displacing the pair. The team also found that the frog is breeding in unnatural sites in disturbed forests, ranging from artificially watered plastic seedling bags adjacent to plant nurseries to rain-filled discarded plastic, glass or metal containers left as trash on the forest edge. “The lack of adequate breeding sites due to habitat loss and competition for limited resources may be driving Charles Darwin’s frog to breed in such unnatural sites. This species may not be able to survive in the face of human dominance and rapidly changing landscapes on the small islands where they live,” Biju said. According to Sonali Garg, a Biodiversity Postdoctoral Fellow at Harvard’s Museum of Comparative Zoology, the frog’s use of trash for breeding is both surprising and worrying. “We now need to know its causes and long-term consequences and devise ways to protect the natural breeding sites that are critical for the survival of the species,” she said.