Mating Anurans: Stories of Procreation from the Sahyadris
Photo StoryPublished : Dec 26, 2024Updated : Dec 27, 2024
Short accounts of some of the reproduction strategies of frogs and toads of the Western Ghats
Text by: Keerthikrutha Seetharaman
Photos by: Dhritiman Mukherjee
Short accounts of some of the reproduction strategies of frogs and toads of the Western Ghats
One mist-filled monsoon night in August, I was at Meghamalai in Tamil Nadu, sampling frogs to test them for diseases. To sample frogs and test them, one needs to find them first. So, my team and I walked towards a spot where we could hear the loudest and most frequent “tik-tik-tik” sounds of bush frogs (Raorchestes sp.). Once we reached the spot, we started looking for them on plants and shrubs — the usual spots where one finds them. After searching for about 10 minutes and nearly giving up, I checked the brick wall behind us and found a whole army of bright Beddome’s bush frogs (Raorchestes beddomii) within a few minutes. They were calling out from the crevices in the brick wall, probably because it amplified their sounds. The calling that monsoon night was to find a mate and pass on their genes.
Mating in frogs is not much different from humans. They woo, and only then can they mate. Wooing or courtship, for want of a more appropriate word, happens in various ways, but calling is the most common. In India, we have nearly 460 species of anurans (a scientific term for frogs and toads), of which nearly 200 are from the Western Ghats biodiversity hotspot. Most species in the Western Ghats or Sahyadris call to court potential females. Calling shows fitness, i.e., the ability of an organism to survive, reproduce and pass on its genes. Often, males who call longer and more frequently are deemed physically fitter. Different species of frogs call from different spots in an area. When a female accepts a male’s call for attention, she will approach the male so they can get into amplexus. “Amplexus” is Latin for “embrace”, during which the male climbs onto the female’s back and holds tight. Fertilisation in anurans is external. While in amplexus, the male and female will find a suitable spot to lay eggs depending upon their species. The female will lay unfertilised eggs, and the male will release sperm onto them to fertilise them.
Imagine a 100-sq-ft area with a small pond and a small stream draining into it. The area has some short bushes (waist high or lower), short trees (waist to shoulder height), tall trees (above shoulder height), and a wetland nearby. In such a setting, there will be some frog species, such as toads (Bufonids) and cricket frogs (Dicroglossids), calling only from the shallow waters of the wetland as they don’t have the physical features like toepads to climb (trees, walls etc.). Some, like tree frogs and bush frogs (Rhacophorids), including (1) various species of Raorchestes, will call from the bushes and short trees. (2&3) The same goes for narrow-mouthed frogs (Microhylids), for they have toepads and a large pad in the feet (known as “subarticular tubercle”) that facilitate climbing. Still others, such as true frogs (Ranids), will call from the stream. This demarcation of boundaries, where certain species occupy specific spots in each area, is called “niche partitioning” and is a result of natural selection, which allows for minimal competition between species for resources.
Sometimes, however, calling alone isn’t enough. It needs to be supplemented by other tactics to show fitness. If, for instance, the niche of a species is in the middle of a fast-flowing stream, its calls can get drowned out by the loud stream, reducing the chances of its presence being noticed, let alone its fitness being recognised. Therefore, (1 & 2) frogs of the family Micrixalidae wave with their legs, making them appear to be dancing, giving them their famed common name, dancing frogs.
Once the calling or waving cue has gained enough attention, a female will approach the male. Anuran females are invariably larger than males, as seen in this photograph of a female (left) and male (right) purple frog (Nasikabatrachus sahyadrensis), a species endemic to the Western Ghats. If all the boxes check out for both, they will get into amplexus. There are many amplexus positions, characterised mainly by how the male holds on to the female.
The purple frog, known to be majorly fossorial (burrowing), will get into a crevice along a stream to lay eggs. (1&2) Dancing frogs, often stream-dwellers, will lay eggs in running streams while travelling over the fast-flowing water in long leaps. I have the good fortune of witnessing a male dancing frog straddle a female and the female leap from rock to rock. The strength of females to achieve this feat truly amazes me. Dancing frogs are known to lay and bury eggs in the streambed of fast-flowing streams, and their tadpoles live underground, feeding on sand and other organisms within. (3) Frogs of the genus Rhacophorus, commonly called tree frogs, are known to lay their eggs in “foam nests” that hang above standing pools of water rather than running water. They lay their eggs in a foam-covered bubble nest, which is speculated to keep the eggs moist and help maintain the micro temperatures essential for tadpole development. The tadpoles of these frogs fall into the waterbody once they are developed from the overhanging nest.
Most tadpoles are known to be filter feeders, feeding on algae and other biomass. They can be found in streams, pools, dam-catchment lakes, and even temporary roadside pools. They usually have suction discs on their mouths that allow them to attach to surfaces and prevent them from being washed away by currents.
Not all tadpoles live in large or obvious waterbodies. For example, tadpoles of some species, such as Ranixalidae (endemic to the Western Ghats), grow on rock faces as the adults lay eggs in the crevices of moist, moss-covered rock faces or even tree-holes.
Some frog species of the genera Pseudophilautus and Raorchestes don’t have a tadpole phase. They are known to undergo “direct development”, where they develop into baby frogs directly from an egg and grow into adults (though the mechanisms involved are yet to be discovered for many species).
The mechanisms involved in the reproduction of many species of anurans remain a mystery. Given India’s tremendous biodiversity, especially in amphibian fauna, there is much work to be done for generations to come. However, given the speed at which infrastructure development is occurring within the country and the threat of rising temperatures, the question we have to worry about is whether there will be many species left when future generations decide to study them.
is one of India's most prolific wildlife and conservation photographers. His work has been featured in leading publications. He is also a RoundGlass Ambassador, and an RBS Earth Hero awardee.
