Our directory of things of interest

University Directory

Darwin’s puddle

Cichlid fish, despite sharing a habitat, are evolving separately Cichlid fish, despite sharing a habitat, are evolving separately Shutterstock
27 Jul
2016
Blue and yellow fish living in a small lake in Tanzania are helping scientists understand basic mechanics of evolution

Speciation is the slow break of a single species into two. Geographical barriers are thought to be the main drive of these splits, when rivers, seas and mountain ranges prevent the genes from intermixing any further than they already have. Take the Asiatic and American black bear for instance – though they share a common ancestor, the two species have become genetically distinct on their respective continents.

But what happens when the geographical location is entirely contained? In a small volcanic lake in Tanzania, what was once a single species of cichlid fish is slowly becoming two, a process known as sympatric speciation. While similar phenomena have been noticed in Lake Malawi – dubbed ‘Darwin’s Pond’ – where more than 875 cichlid species have evolved from just a handful of ancestors, it is the far smaller Lake Masoko – nicknamed ‘Darwin’s Puddle’ – that the secrets of sympatric speciation are beginning to be realised. At just 700 metres wide, it is a mystery how the pond’s fish can possibly separate their gene pools. Yet that is precisely what is happening.

We may begin to see continents and oceans as active places where evolution of diversity is continually in progress

‘The two cichlids now have different features,’ says George Turner, a biologist at the University of Bangor who has been studying their genetics. ‘They have different colours, habitat preferences, behaviour, diet and morphology.’ The ‘littoral’ cichlid is yellow and prefers shallower water, while the ‘benthic’ cichlid is blue and prefers a deeper habitat. However, the difference in depths doesn’t count as geographic isolation, as both species frequently move between the two and are often found alongside each other. So why did they stop mating? ‘It must have something to do with sexual selection and mate choice by females,’ theorises Turner. ‘What we want to know is whether sexual selection initiates speciation, or if it comes into play later after some other process has started it off.’

Turner believes that the Darwin’s Puddle cichlids could shake-up our understanding of evolution. ‘If we can figure out how sympatric speciation can happen in a tiny crater lake, then we have to ask ourselves whether we think the same thing can happen on continents and in oceans, where most species live,’ he says. ‘Without proposing scenarios of geographic barriers every time a new species evolves, we may begin to see continents and oceans as active places where evolution of diversity is continually in progress.’

This was published in the August 2016 edition of Geographical magazine.

Related items

Julysub 2020

geo line break v3

Free eBooks - Geographical Newsletter

geo line break v3

geo line break v3

University of Winchester

geo line break v3

EDUCATION PARTNERS

Aberystwyth University University of Greenwich The University of Derby

TRAVEL PARTNERS

Ponant

Silversea

Travel the Unknown

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in PLACES...

Cities

Scientists are using sophisticated data modelling to predict how cities…

Places

The most populated country of Central Asia, Uzbekistan has been…

Forests

To protect the forests that act as natural carbon reservoirs,…

Forests

Recent research finds that climate change-induced drought is having a…

Cities

The city of Calais struggles with its reputation. More often…

Mapping

Benjamin Hennig and Tina Gotthardt map the coronavirus

Water

The controversial practice of cloud-seeding has always been difficult to…

Forests

The impact of wildfires on water supplies has received little…

Mapping

Benjamin Hennig maps the two sides of global malnutrition –…

Cities

Thomas Bird reports on the coronavirus, speaking to those trapped…

Forests

The world’s second largest tropical forest receives significantly less funding…

Cities

The world’s first water-borne dairy farm has been erected on…

Cities

Continental Europe’s most extensive underground rail transport network, the Madrid…

Cities

A central highway in Brazil’s largest city is about to…

Cities

Urban photography marries themes and passages from TS Eliot in…

Mapping

From Leonardo da Vinci’s genius and the history of Starbucks,…

Mapping

How do you usually travel to work? Question 41 in…

Water

The Nile is home to mysteries both ancient and modern…

Places

While researching his main article on the world’s smallest countries,…

Places

Vitali Vitaliev briefly meets the down-to-earth ruler of Liectenstein