In the Andaman Islands along the eastern coast of India, a species of frog mates and lays eggs while in an upside-down position, BBC reports a new study.
Indian and American scientists have found that both male and female Charles Darwin frogs position themselves upside-down above tree cavities, their bodies separated from the water. Newly hatched tadpoles will fall into the water below and develop into free-swimming tadpoles.
Indian biologist Sathyabhama Das Biju commented: “This is remarkable. Laying eggs upside-down is the most unique behavior in this frog species. No other frog species is known to lay eggs above tree cavities in an upside-down position, with their entire bodies separated from the water.”
Nearly all of the 7,708 frog species in the world mate and lay eggs in water and some other terrestrial habitats. Females lay eggs during mating, while males release sperm to fertilize them.
A group of Indian and American biologists from the University of Delhi, Zoological Survey of India, Harvard University, and the University of Minnesota camped for 55 nights over three years during the rainy season to study the reproductive behavior of Charles Darwin frogs. Their latest research was published in the scientific journal Breviora.
The uniqueness of this species doesn't stop at their mating behavior. Even the way they call each other for mating is different.
Researchers discovered that males typically have three calls to attract females. When the aggressive sounds of males fail to drive away competitors, they start fighting, using their limbs to kick and punch. They even bite off body parts, including the heads of their rivals.
If a male successfully climbs onto a female, nearby males may fight with the mating pair. They even try to wedge themselves between the mating frogs to separate them.
Mr. Sathyabhama Das Biju pointed out: “In our observations, fights between males rarely result in death. The level of aggression in this species is surprising, such as the behavior of biting off body parts.”
The upside-down mating behavior has evolved to prevent aggressive males from disrupting the egg-laying process by intruding on mating pairs.
Mr. James Hanken from Harvard University, a member of the research team, said: “This discovery is an example of the diversity of amphibian species and reproductive behaviors that science has yet to uncover. Especially in unexplored regions within Asia's biodiversity hotspots.”
Charles Darwin frogs, named after the famous naturalist, are found only on a few islands in the Andaman archipelago and nowhere else. They are not common and exist only in specific forest environments. The International Union for Conservation of Nature (IUCN) lists this species as “near threatened” due to fragmented populations and habitat decline.
