Waist-deep in a stream, in the Kalakad Mundanthurai Tiger Reserve (KMTR) in Tamil Nadu, K S Seshadri was busy catching, measuring and releasing frogs as part of an amphibian survey of the region. The selective logging of trees that happened in KMTR some 40 years ago had created marked differences in vegetation, the butterfly population, and mammal distribution between logged and unlogged areas of the forest. Pursuing his master's degree in ecology and environmental sciences from Pondicherry University at the time, Seshadri, along with his two assistants, was out in the field that night amassing amphibian data.
One of his assistants suddenly turned away from the frog in his hand to look up. "Anna, leopard!", he said under his breath. All three headlamps now shone like a spotlight on the wild cat, just about eight feet away, attempting to cross the stream. Seshadri managed to pull out his camera and shoot a shaky video before the leopard ducked behind the rock and disappeared. Out of sight, but not out of mind, the three-man crew decided to abandon sampling for the night and head home.
Frog research is not often a matter of life and death, but drudging through lakes, ponds and streams in pitch darkness with just a headlamp for guidance is very much the status quo. K S Seshadri has spent the last decade and more dedicated to understanding why and how species behave the way they do by studying frogs. In 2018, he completed his PhD in biological sciences at the National University of Singapore on a 'Prof. Navjot Sodhi Scholar for Conservation Biology' scholarship. His doctoral thesis reports the discovery of two new species and a novel reproductive behaviour among all amphibians. Seshadri has subsequently worked as the Research Director at the Agumbe Rainforest Research Station (ARRS) and is currently a Department of Science and Technology-INSPIRE Faculty Fellow, at the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc), Bangalore.
From the latest on frog vocalisations and how colour patterns are related to parental care in frogs to a pilot study on the thermal tolerance of frogs and how climate change could potentially prove fatal—we bring you plenty of frog talk this World Frog Day (March 20th).
Over to K S Seshadri to tell you why these tiny lifeforms are so ‘croaking’ important that he made them his life’s work. The following is an edited transcript of the interview.
Before we talk frogs, briefly tell us about your journey from a hobbyist bird watcher to a career in ecology?
A lot of it has to do with me signing up for wildlife-related activities, especially birdwatching. That is really the short version of how I got into research. Through my birdwatching circle, I started getting involved with a group that later came to be known as Growing Wild, who would go out and do fieldwork whenever the Centre for Wildlife Studies (CWS) needed volunteers for their research work. I was an undergraduate student at St Joseph’s College, Bangalore, and I would take any break I could get—all my summer vacations—to volunteer for fieldwork. Later, through my birdwatching contacts, I met Gururaja K V, who at the time worked at CES, IISc, Bangalore. During my BSc, I had only studied Botany, Chemistry and Environmental Science and knew nothing about frogs. I joined Gururaja on one field trip, and we designed a study on roadkills of frogs. A few months later, we even managed to publish a paper. That cemented my role in science or ecology and transformed me from being a volunteer to a researcher.
Over the last decade, you have more or less focussed your efforts on amphibians. Why and how did that come about?
Mostly because nobody else has been doing the stuff I have been doing or asking the kind of questions I am keen on knowing. A lot of the science so far on amphibians has been about taxonomy, systematics, describing new species, range extensions etc., which is great and absolutely essential. But because of my training and prior work experience with ecologists, I was of the belief that there is more to a species or a system than knowing its name. It has shaped the science I like to do now.
I have, over the years, taken a holistic approach by including aspects of systematics, taxonomy, community ecology, animal behaviour, and evolutionary ecology. The great thing about using amphibians as a model system is that we know so little about them. The answer to most questions such as what do they eat or why do they behave in a particular way is often: ‘We don't know. Let's find out!’.
You have published two papers this year. The one on vocalisations is really interesting! You investigated whether frog calls can convey contextual information? What were your major takeaways?
The paper was essentially Shikhara's (Ananda Shikhara Bhat), an undergraduate student from Pune who worked with my colleague Anand Krishnan. He had gone out to the field and observed that the Humayun's Night Frog (Nyctibatrachus humayuni), a medium-sized aquatic frog, when calling alone, had one call, but when there was a male around, was adding a note to the end of the call.
First, we documented the repertoire size, which is the number of different notes an animal can produce. Notes are the subcomponents of a call. A single call may have one or more notes. In our case, we knew that the Nyctibatrachus humayuni had a two-noted call. Through his documentation, Shikhara was able to show that when there is a male around, the individual is adding more notes to his call. But we wanted to compare this with another species, either within the same genus or same family and see how context-dependent communication has evolved. Unfortunately, with COVID restrictions, we couldn't do that, and Shikhara studied the Pseudophilautus amboli, a small brown bush frog from a completely different family (Rhacophoridae), in which we found that it had a much larger repertoire size. He documented that they can produce six different note types. Again, we looked at in what context they are making which call, and turns out, even in these frogs, the six notes are split into two groups. One note group was either in the context of advertisement or mate-finding when the male is alone, and the other group was more in the aspect of territorial conflict-resolution.
We then drew up a co-occurrence matrix to see which note types are emitted more often with which note types so that we can assign a syntax. You measure it as Shannon entropy, which in simpler words can be equated to vocabulary. On examining their Shannon entropy, although one frog has a larger repertoire size than the other, we found that both produce complex calls or sequences. All of which taken together tells us, in a simple broad sense, that frogs are capable of complex vocal communication. There was this notion that vertebrates are the most evolved in this aspect, but not really. Frogs too, at their level, have complex communication systems.
Now it opens up a whole set of questions, as to its evolutionary value. One simple thing we might do is playback experiments to see how females perceive these calls. In other species from South America, we know females prefer complex calls. Then there is the aspect of predation. When making complex calls, the chances of being heard by predators is more. How does a calling male then solve the trade-off between the risk of predation versus the benefit of finding a mate?
You've written a couple of papers on parental care in frogs. The latest one studies the correlation between parental care and colour patterns. How did you come upon this question?
In many bird species, the female is dull and drab, and the male is bright and colourful. The notion is that because of sexual selection, one sex is brighter and more conspicuous than the other for being able to attract mates. For instance, the female may find the more colourful male attractive, but by being bright and conspicuous, there is an increased risk of predation. The female is often dull and drab, and this may help overcome predation. Plenty of bird literature points to this explanation, and you have people reporting this pattern multiple times. While reading a few papers on parental care in frogs, I started thinking, ‘Oh wait, frogs are colourful, and there is also predation. How do colours and patterns help overcome the risk of predation during caregiving activities?’ Parental care is costly, for instance, a caregiving adult cannot go out to feed as often or find mates elsewhere. Then there is also sexual selection where one sex is brighter than the other—called sexual dichromatism. Many studies suggest that the cost of predation on a dichromatic pair is different. Among frogs, we see species like the male Indian Bullfrog with bright yellow mating colours. We wanted to explore how dichromatism is related to parental care as well.
Turns out that among the species that care, a vast majority of them are not sexually dichromatic. If dichromatism was to be associated with parental care, we expected the duller coloured sex to care—this was not the case. We then moved on to examine if specific colours or patterns were correlated with the occurrence of care as well as the sex of the caregiver. We examined dorsal colours and patterns of 988 species belonging to 45 families, separately for males and females, to categorise them into different colours and patterns. We then used a phylogenetic comparative analysis, which includes the genetic relatedness of species to test for relationships of colour, pattern, and parental care. We found that care was independent of colour, irrespective of which sex cared. It means that a frog could be any colour and still care or not care. Among patterns, we found that only those species in which the males cared, they were likely to have stripes on the dorsum. Now stripes probably have some selective advantage among male parental care, but we don't know what it is. It could be things like motion dazzle, where an animal with longitudinal stripes leaves the predator incapable of correctly gauging the direction and speed of motion. This has been previously studied in snakes.
Our findings only pave the way for further questions. Why only species with longitudinal stripes? Why not cryptic or aposematic species? We need more people to go out and document the presence of parental care and actually test if specific patterns are helpful to avoid predation. The future is bright and hopeful.
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What are you currently working on? Anything you can tell us?
My most recent work looks at the thermal tolerance of anurans (frogs and toads). Every animal has an optimal range of temperature in which an animal can operate, above and below which they tend to perform less or die. With frogs and generally with reptiles, because they are ectotherms (dependent on external sources of body heat), the atmospheric temperature plays a key role in their life history and physiology.
Generally, with reptiles and amphibians, we measure two things—CTmax and CTmin (CT—Critical Temperature). The difference between CTmax and CTmin will give me the thermal breadth, the breadth of temperatures a species can tolerate. These tolerances can be variable within species depending on the environment in which they evolved. In a place like Bangalore, which is rapidly urbanising, species tolerances may vary as they have to adapt to increased temperatures in cities. Using satellite images to quantify urbanisation, my colleagues and I are sampling different lakes for frogs with the hope of comparing thermal tolerances of different species of anurans.
All of this feeds back to animal physiology because heat tolerance is based on a class of proteins called heat-shock proteins found in every cell of all organisms. The reason why heat-shock protein is important is that it is something that is evolved. So different lineages of amphibians would have evolved such proteins in relation to their ambient temperatures in which they operate. If the temperature changes beyond their ability to regulate (because climate change is happening now and not over an evolutionary timescale), it will likely be beyond the ability of the frog to cope with that change. Eventually, I would want to ask similar questions about anurans in the Western Ghats.
You have studied amphibians for more than a decade. What would you say are the major threats they face?
In the Indian context, the loss of habitat is huge for frogs. When I say that, people tend to think of the construction of large dams or the cutting down of forests like they do in Brazil, but what we also have is things changing at a much smaller scale. Something as simple as tourists visiting a stream inside a forest can have a profound impact on local frog populations.
Then there are dams and roads, of which we don't have any notion of containing their impacts. In Sakleshpur, for example, we have built check dams to supply water to Bangalore. On the face of it, the impact seems minimal, but the stream hydrology is getting altered completely. Of course, we have roads being constructed everywhere. Apart from being a barrier for wildlife, there are other impacts. Every time a road cuts through a habitat, it creates two edges. There will be an increase in temperature, humidity and the sound profile changes, and this starts spreading inwards. In agricultural fields, pesticides are pumped in with no regulatory mechanisms in place. It is a big laundry list that is endless.
The big elephant in the room is the chytrid fungus (an infectious disease that affects amphibians worldwide), which has been found in India, but nobody is monitoring it. If you ask me where chytrids are found, I can tell you where, but all of these data points are at least ten years old. Not just frogs, one of the biggest challenges to biodiversity in India is a lack of monitoring. We don't have a long-term monitoring programme for anything. Tigers, yes, maybe. With other things, you have no idea. It is scary! It will be so late by the time we realise something is going extinct that we would have gone past the point where we can fix it.
One of the things we have been involved in is Project Ashoka at Gubbi Labs in the Western Ghats, where we have a few sites that are being monitored every few months. It has been going on for the last seven years now. The idea is that 20–30 years down the line, we will know if something is changing. This effort needs to happen, it is not difficult to do, but it needs to happen more frequently across India.
Why are frogs important? What message do you have for the younger generation?
One thing I would tell the younger generation is to lose the camera and look at the animal. As much as cameras are important, I think there is something to learn from looking at animals and observing them. I can't emphasise enough the importance of maintaining field notes—human memory is fragile—it is always good to write things down while in the field. Not just youngsters. Everybody. Sometimes, I have to remind myself, 'Ok, enough with the camera'.
Why are frogs important? Every component of an ecosystem is important. Maybe the next major discovery from the medical sciences will come from frogs. We don't know! I think it is worth taking some time to appreciate the diversity of our world. It is important to cherish what we have because we can lose it very quickly. That will be my take on why frogs or any other animal, for that matter. We can only conserve what we have. Once lost, we can't do anything about it.
