Andamanese Charles Darwin鈥檚 frogs breed like no other frog: clinging upside down to the side of partially flooded tree cavities. This inverted addition to the Kermit Sutra may be positioning the frogs in such a way that they can kick away male competitors.
and , both at Harvard University, were studying amphibians across India and nearby regions with colleagues at the University of Delhi. During field surveys in the Andaman and Nicobar Islands in the Indian Ocean, the researchers noticed the native Charles Darwin鈥檚 frog (Minervarya charlesdarwini) breeding in hollows in trees rather than puddles or ponds as its close relatives do.
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Intrigued, the researchers studied the frogs鈥� mating habits from 2019 to 2022 in South Andaman Island鈥檚 forests, recording and analysing their catalogue of calls and filming their breeding behaviour.
During mating, the male grasps onto the back of the female in amplexus, a manoeuvre common in frogs that can last hours to days. Wearing the male like a backpack, the female crawls up and out of the pool, turning around. Upside down and backing up, she then lays her gelatinous eggs along the inner wall of the tree. When the tadpoles hatch, they plop into pooled water below, which gathers in these cavities.
No other frog is known to breed this way, says Biju, laying eggs in a tree hole while being out of the water and upside down.
The upturned pose may be an adaptation that evolved to help the frogs deal with large numbers of aggressive, unpaired males in the tree hole pools. Such males will bite and kick each other in competition for mates, and will try to pry apart mating pairs.
鈥淪he just turns upside down and lays [the eggs] up there where there are no males,鈥� says Garg. Pointing her rear away from the water may also make removing her mate more physically demanding for the intruders.
at the University of Newcastle in Australia wonders if the female turns upside down so that she can see where her offspring are most likely to drop after they hatch before depositing her eggs.
鈥淚t might improve the chance and guarantee that her offspring fall directly into the water,鈥� he says.
Breviora
