Frog found only in Andaman has unique breeding ritual. It lays eggs upside-down

What sets this species apart is its distinctive upside-down spawning posture, with mating pairs orienting themselves vertically on tree cavity walls, completely out of the water.

In Short

• What sets this species apart is its distinctive upside-down spawning posture
• Mating pairs orient themselves vertically on tree cavity walls
• Upside-down spawning is the most remarkable behaviour in this frog

A team of international biologists has uncovered a remarkable breeding behaviour in the Andamanese Charles Darwin's frog (Minervarya charlesdarwini), an endemic species to the Andaman Islands.

The new study, published in the Harvard Museum of Comparative Zoology's journal Breviora, reveals a combination of traits that make this frog's reproduction truly unique.

The research, led by Professor S. D. Biju of the University of Delhi, describes how these frogs breed and deposit terrestrial eggs above the water surface on the inner walls of water-filled tree cavities or root buttresses.

What sets this species apart is its distinctive upside-down spawning posture, with mating pairs orienting themselves vertically on tree cavity walls, completely out of the water.

"Upside-down spawning is the most remarkable behaviour in this frog. No other frog is known to lay terrestrial eggs inside tree holes in an upside-down position," said Professor Biju, currently a Fellow at the Harvard Radcliffe Institute.

The study also highlights the complex mating rituals of these frogs. Males produce three different types of advertisement calls to attract females and engage in aggressive physical combat, including kicking, boxing, and biting, to compete for mates. The researchers suggest that the unique upside-down spawning behavior may have evolved as a strategy to prevent unpaired males from disrupting egg-laying.

Professor James Hanken, a study co-author and Curator of Herpetology at the Museum of Comparative Zoology, emphasized the significance of this discovery: "This finding 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."

However, the study also raises concerns about the species' conservation. Researchers observed frogs breeding in unnatural sites such as plastic containers and discarded trash, possibly due to habitat loss and competition for limited resources. This adaptation to human-altered environments highlights the urgent need for conservation efforts.

Sonali Garg, a Biodiversity Postdoctoral Fellow at Harvard's Museum of Comparative Zoology and co-lead of the study, stressed the importance of protecting the frog's natural breeding sites: "The frogs' 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 survival of the species."

The study calls for increased attention to the conservation of this endemic and threatened species, currently listed as "Vulnerable" on the IUCN Red List. As human activity continues to impact the Andaman Islands, protecting the specialized microhabitats of the Andamanese Charles Darwin's frog becomes crucial for its survival.