- In conversation with Linnean Medal winner Rohan Pethiyagoda
The world of animals and plants, or flora and fauna, as naturalists would call it, is certainly fascinating to even the most casual observer. This is especially true in a country like Sri Lanka which has such a rich biodiversity – from the famously charismatic species like the elephant and leopard to the species that often fly under the radar like frogs and fish.
Being such a diverse hotspot, Sri Lanka has produced many eminent naturalists – one of whom has just been awarded an immense honour in the world of biologists; the Linnean Medal. Rohan Pethiyagoda, one of the winners of this year’s Linnean Medal (the Medal is awarded to up to two biologists each year and the other medal was awarded to Ethiopian botanist Professor Sebsebe Demissew) is one of Sri Lanka’s most eminent naturalists and taxonomists. His 1991 book ‘Freshwater Fishes of Sri Lanka’ was hailed as a landmark achievement, painting a more comprehensive and authoritative picture of Sri Lanka’s freshwater fish than ever before.
Rohan went on to found the Wildlife Heritage Trust (WHT), a platform that has allowed other naturalists to discover and document Sri Lanka’s biodiversity as well as enhance the biogeography of the broader region. His programme of original and collaborative research (both Sri Lankan and overseas) has resulted in publications on many zoological groups in addition to fishes.
In the wake of being awarded the Linnean Medal, Brunch reached out to Rohan for a chat on the award, taxonomy, and what has driven his passion for Sri Lanka’s frogs, freshwater fish, and the countless other small animals that play hidden roles in our island’s ecosystems.
Winning the Linnean Medal
The Linnean Medal was instituted in May 1888 by the Linnean Society – the world’s oldest active society devoted to natural history – in connection with the Centenary of the Society that year. The Society takes its name from Swedish naturalist Carl Linnaeus (1707–1778), widely considered to be the Father of Botany and Zoology, whose botanical, zoological, and library collections have been in the Society’s keeping since 1829.
The Linnean Medal is awarded annually by the Society alternately to one or two biologists (in any field), as an expression of the Society’s esteem and appreciation for service to science.
For Rohan, the Medal came out of the blue. “It was entirely unexpected. It has been given to very eminent people, and I didn’t think I was even eligible,” Rohan shared. “This isn’t something you make an application for, and everyone who has received it previously has been a very eminent biologist. I feel absolutely humbled and honoured to have been awarded this.”
Being a taxonomist
In biology, taxonomy is the scientific study of naming, defining (circumscribing), and classifying groups of biological organisms based on shared characteristics. With Rohan being recognised for his tireless work as a zoologist and taxonomist, Brunch asked what exactly makes a naturalist a taxonomist.
“The job of a taxonomist is to describe species. Everyone in natural history and biodiversity studies starts their life thinking about taxonomy and what makes each animal different,” Rohan explained, adding practical context to the art of taxonomy: “For example, we know that Sri Lanka has about 500 species of birds, but how do we know what a species is, to arrive at that count? A taxonomist’s job is to examine a species from several different angles. Take a frog, for example. Looking at the anatomy of the frog, its ecology, its distribution across habitats, its behaviour and its DNA, a taxonomist would use all of this evidence to decide whether it is the same species of frog you thought it was at first glance or if it is a different species altogether. With some animals, this is easy. Humans and chimpanzees are each other’s closest relatives in terms of evolution, but you can see very obvious differences. In the natural world, species can be more difficult to tease apart, and that’s where a taxonomist comes in.”
While being a taxonomist sounds like a very technical form of work (and it is), this doesn’t mean taxonomy is something reserved only for science and the scientific mind. As Rohan puts it, “Everybody is a taxonomist – human beings have a habit of naming things. Ordinary people in an ordinary village have a name for every plant and animal around them and know that each is different.”
What’s in a name?
Over the course of his career, Rohan, together with his colleagues at the Wildlife Heritage Trust, played a part in identifying, naming, and describing over 100 new species of vertebrates from Sri Lanka, including fishes, amphibians, and lizards, in addition to 43 species of freshwater crabs. So how does one name a species?
“Every species has two names, like a surname and first name – there is an international code that governs such things – the International Commission on Zoological Nomenclature (ICZN). Each taxonomist is allowed to pick a name of choice with a Latin descriptor. If the animal being named is green, for instance, the descriptor could simply be viridis, which is green in Latin. You could also name an animal after a place, or, if you want to honour somebody, you can name it after a person. For example, I once named a fish after the naturalist Dr. P.E.P. Deraniyagala.”
In fact, Rohan has had several new species named after him (by other scientists) including the fishes Dawkinsia rohani and Rasboroides rohani, the microhylid frog Uperodon rohani, the dragon lizard Calotes pethiyagodai, the jumping spider Onomastus pethiyagodai, and the dragonfly Macromidia donaldi pethiyagodai. In 2020, a team of scientists led by S.D. Biju named a new genus of South and Southeast Asian tree frogs Rohanixalus in his honour as well.
Reflecting on how it feels to have such a legacy behind him, Rohan said: “You do feel very honoured by such a thing. The famous scientist Richard Dawkins, when I named a genus of fish after him, said he felt like he’d been given a little piece of immortality. A species’ name lives forever – many of the names we’re using now are 200 years old, and in another 200 years, they’ll still be around. I can’t put it better than Dawkins himself – it is a bit of immortality. A hundred years from now, people will wonder who this fellow Rohan was!”
Why is naming species so important? From a naturalist’s standpoint, taxonomy and naming species is a big deal. It is arguably the most important singular point of reference you can have. “Unless you name and describe a species you can’t do anything with it. You can’t form a conservation plan, you can’t know if it is at risk, or argue for its protection. Naming it means people can continue to identify it, study it, and recognise it in its own right. And of course, conserve it. As far as the public is concerned, people appreciate species – the fact that Sinharaja has such rich biodiversity is appreciated by everyone because of the number of species it contains – the public appreciation of nature often comes down to species.”
Sri Lankan ichthyofauna
As a naturalist, Rohan is known as an expert on fish and other fauna in and around our freshwater water bodies. This is in no small part due to his comprehensive book ‘Freshwater Fishes of Sri Lanka’ and the dozens of scientific papers he has published. The proceeds of ‘Freshwater Fishes of Sri Lanka’ were what Rohan used to form the Wildlife Heritage Trust and create a platform for Sri Lankan naturalists with limited resources to work. The Trust has continued to help fund outstanding young biodiversity scientists to this day.
Brunch asked Rohan what he could tell us about the current context of freshwater fish in Sri Lanka. “We have about 90-100 freshwater fish species, which is not a lot, and half of these species are endemic,” he explained, adding that in comparison to other areas close to Sri Lanka, like Southern India, the number of species Sri Lanka has is low. The reasons for this dearth of fishes in the island’s otherwise exceptionally rich biodiversity landscape are unclear.
One theory among naturalists is that in prehistoric times (sometime in the last few million years), there was a desiccation event in which the island’s rivers and streams dried up for lack of rainfall. It appears, however, that some groups of fish survived this catastrophe in the southern rainforests in the Sinharaja-Galle-Matara triangle, which is where most of Sri Lanka’s most ancient endemic fishes live today. “The island’s south western quadrant seems to have been a refuge for freshwater fish,” explains Rohan. “A few survived, but the rest of the island suffered a massive extinction. This would explain why the island’s fish fauna is not more diverse, as in southern India.”
What threats are Sri Lanka’s freshwater fish facing today? From Rohan’s perspective, it’s tough to say, as his views have changed over decades of observation. “Twenty-five years ago, I used to think there were a lot of threats,” he said. “At that time I thought that extinctions were imminent because of pollution and other external factors. But it looks like Sri Lanka’s freshwater fish are quite resilient, and many of the threats we thought of as major may not be so serious. That’s a relief, of course, but it is not to say we can be complacent!”
“We have lost more than 90% of our wet zone forests, but so far as we know, no fish species except perhaps in the highlands. Even with amphibians, we have 119 species, of which maybe 90% are endemic. We thought many were extinct because we couldn’t find them in the early ’90s. But now, scientists such as Mendis Wickramasinghe are discovering that some of these species are alive and well,” Rohan said, stressing that while this is a happy occurrence, it is by no means a green card for irresponsible environmental and ecological behaviour.
Looking back on a career in taxonomy
As someone who has devoted his life to the taxonomy of small animals and fish, we asked Rohan what made him pick smaller animals as his main area of focus. “Large animals tend to be well known,” he argues. “I’ve never been attracted to the idea of large mammals because they’re so well understood. You have hundreds of people working on them. To date, in Sri Lanka, you might have 20 people studying leopards, but very few studying insects. I felt it was important to focus on the small things because they’re just as important, and so many of these smaller animals are endemic to Sri Lanka and could disappear even before they are discovered.”