Quote and original copyright -The Island Paper By Rohan Pethiyagoda & Hiranya Sudasinghe

Nations Trust WNPS Monthly Lecture

6pm 18th September 2025, Jasmine Hall, BMICH

Well over 2.5 million Sri Lankans visit national parks each year. We can conclude from this that a great many of us love nature and want it conserved. For the most part, we see nature primarily through the lens of species which, together with landscapes and ecosystems, constitute what we commonly call ‘biodiversity’. We rarely stop to think, however, of the processes that give rise to our astonishing biodiversity. Evolution by natural selection, the most important of these processes, was discovered by Charles Darwin 165 years ago. But despite the passage of so much time, scientists continue to be perplexed by some of the mechanisms by which species evolve.

Sudasinghe & Pethiyagoda

Taking Sri Lanka’s freshwater fishes as an example, this month’s Nations Trust-WNPS lecture will seek to unravel the evolutionary processes by which this remarkable diversity came to be. The lecture, written in collaboration with Hiranya Sudasinghe, will be delivered by Rohan Pethiyagoda. Aged just 33, Sudasinghe has been exploring freshwater fishes since his childhood. He eschewed a career in medicine to study zoology, securing a first-class in his BSc at Peradeniya and going on to an MPhil in fish systematics.

He has discovered and named seven new species and three new genera of fishes, and despite his youth, is the author of more than 30 papers in international journals. He also went on to rediscover two species which were long thought to be extinct. He is presently in the final year of his PhD programme at the University of Bern, Switzerland.

Rohan Pethiyagoda first came to national attention in 1991, when he published his landmark book Freshwater Fishes of Sri Lanka which, for the first time for any group of the island’s plants or animals, contained colour photographs of every species then known. He says he has lost count of how many books and papers he has published, among which numbers The Ecology and Biogeography of Sri Lanka: a Context for Freshwater Fishes (2021), which he co-authored with Sudasinghe.

Pethiyagoda’s contributions to biodiversity science and conservation have been recognized by his being awarded the Linnean Medal for Zoology, a Rolex Award for Enterprise, and a fellowship of the National Academy of Sciences.

Rohan Pethiyagoda

Hiranya Sudasinghe

Multiple Extinctions

“Sri Lanka contains around a hundred species of freshwater fishes”, says Sudasinghe. “Especially in the highlands, fishes have suffered multiple extinction events in the past, most likely due to prolonged droughts. After those extinctions, species that survived in small rainforest refuges in the South dispersed across the country and went on to diversify. Meanwhile other species colonized Sri Lanka via the Palk Isthmus, the land bridge that connected us to India when sea levels were low. Today, DNA analyses show many of these ancestral colonizers evolving into genetically distinct species or incipient species. It is fascinating to watch evolution at work.”

Sexual Selection

Pethiyagoda adds that another example of evolution at work is the elongated filaments trailing from the dorsal fin of species of Dawkinsia, a genus he was instrumental in naming after Richard Dawkins, the author of The Selfish Gene, in 2012. “These fish are superb examples of sexual selection, rather like the peacock. But, as we will explain in the lecture, the story is much more complex than that: it is profoundly mysterious.”

Pethiyagoda says that evolution in Sri Lanka’s freshwater fishes can be useful to understanding evolution even in humans. “It’s uncanny. We are evolving according to principles that were trialled by fish tens of millions ago. The same evolutionary playbook is still in use.

Pethia Reval

Belontia Signata

Systomus Asoka

Hiranya and I want to share this story with the nature-loving public for the first time. I doubt whether anyone else has really thought about Sri Lankan freshwater fishes, or any other group of animals for that matter, in this way before.”

Climate Change

“Hiranya is the first scientist to have shown that mass extinction events have occurred in Sri Lanka,” he adds, “most likely due to climate change. This is a harbinger of what might lie ahead as the planet enters a new spasm of rapidly changing climate. Fish are at very high risk.

We want to use this opportunity to explain why it is not just species that we need to preserve, but also the evolutionary processes that give rise to them. It is a different way of looking at conservation.”

Pethiyagoda and Sudasinghe say that they want to give the public a fish’s eye view of conservation from an evolutionary perspective. “Up to now, we have been thinking about conservation in a really archaic way”, says Pethiyagoda. “But the fine-scale distribution data we now possess, coupled with genetic analyses, have paved the way for an altogether new approach. We need to think in a finer resolution than just ‘species’. By themselves, Red Lists and protected areas simply will not work.

Future generations will not forgive us if we fail to drag conservation into the 21st century, applying the best scientific tools available. Conservation is now an advanced science, and it will be impossible to save Critically Endangered species without invoking the best scientific practices available. We want to use this lecture to outline some of these methods and try to chart the way ahead.”

The lecture, which is open to the public, will be delivered at 6 p.m. on Thursday 18 September at the Jasmine Hall, BMICH.