Dr Hiranya Sudasinghe: Can Two Identical-Looking Fish Carry Different Histories?

STORY 2 OF 10: Part of a series of short stories inspired by our conversation with Dr Hiranya Sudasinghe, sharing what years of experience have taught them to see.

Place two small fish in a shallow glass tray and they may appear identical.

Same size. Similar markings. The same mildly unimpressed expression.

The fish may disagree.

One population may have lived in a river basin for generations without mixing with another. During that separation, the two populations may accumulate different inherited genetic characteristics even while retaining similar outward appearances.

Dr Hiranya studies these hidden relationships.

DNA extraction robot. Photograph courtesy of Hiranya Sudasinghe.

A genome is not a diary written in complete sentences.

It is more like an enormous family archive in which scientists search for evidence of relationships, separation, movement and past decline.

DNA can also retain signs of a population bottleneck.

A bottleneck occurs when a population becomes extremely small and loses part of its genetic variation. Even if the number of animals later increases, the missing variation does not automatically return.

This can matter when a threatened species requires active recovery.

Scientists may need to know which populations retain the greatest or most distinctive variation.

Genetics does not decide the conservation plan by itself. Habitat, disease, numbers, local threats and ecological suitability also matter.

But it can prevent every surviving population from being treated as though it were interchangeable.

Hiranya’s words that inspired this story

“I started to understand the genetic patterns, like how the different populations of a species in Sri Lanka are genetically clustered, and to gain more insights into the evolutionary relationships within the Sri Lankan freshwater fishes.”

“We talk about biodiversity in general, but it includes three pillars: ecosystem diversity, species diversity and genetic diversity.”

“When a species is at the brink of extinction or when there’s a bottleneck, we need to understand what populations still have that large diversity that could still potentially be used.”

Why it matters

Suppose one fish species survives in three rivers.

If conservation protects it in only one river, the species name may survive while two distinct parts of its genetic history disappear.

Saving the species somewhere may not be enough.

Different populations may retain

• Different genetic variation

• Different adaptations

• Evidence of long separation

• Different capacities to respond to changing environmental pressures

  
  

What this changes

A stream is not merely another place containing the same fish.

It may hold a population with inherited variation absent from populations elsewhere.

The fish may be carrying different chapters of the same larger story.

Next beneath the surface

Those separate populations may depend on a connected stream system that refuses to remain inside a protected boundary.

Next: Why Can’t a Protected Forest Protect the Stream Running Through It?

Previous: What Happens When Conservation Gets a Fish’s Name Wrong?

Meet Dr Hiranya: Read He Chose the Fish