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.

Share this story...

Submit to FacebookSubmit to Google PlusSubmit to Twitter

Related items

Leave a comment

ONLY registered members can leave comments and each comment is held pending authorisation before publishing. Please login or register to voice your opinion.

Geographical Week

Get the best of Geographical delivered straight to your inbox every Friday.

Subscribe Today

EDUCATION PARTNERS

Aberystwyth UniversityUniversity of GreenwichThe University of Winchester

TRAVEL PARTNERS

Ponant

Silversea

Travel the Unknown

DOSSIERS

Like longer reads? Try our in-depth dossiers that provide a comprehensive view of each topic

  • National Clean Air Day
    For National Clean Air Day, Geographical brings together stories about air pollution and the kind of solutions needed to tackle it ...
    REDD+ or Dead?
    The UN-backed REDD+ (Reducing Emissions from Deforestation and Forest Degradation) scheme, under which developing nations would be paid not to cut dow...
    The true cost of meat
    As one of the world’s biggest methane emitters, the meat industry has a lot more to concern itself with than merely dietary issues ...
    Long live the King
    It is barely half a century since the Born Free story caused the world to re-evaluate humanity’s relationship with lions. A few brief decades later,...
    London: a walk in the park
    In the 2016 London Mayoral election, the city’s natural environment was high on the agenda. Geographical asks: does the capital have a green future,...

MORE DOSSIERS

NEVER MISS A STORY - follow Geographical

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

The next stage in autonomous vehicles is hoping to transform…

Mapping

Geographical’s resident data cartographer presents a true picture of the…

Water

What impact could an unprecedented incident of ‘river piracy’ have…

Mountains

Norway is to undercut a mountainous peninsula to create the…

Mapping

Benjmain Hennig explores global mortality with maps

Water

Last winter’s cold conditions contributed a further influx of road…

Water

As one of America’s biggest cities, supplying clean drinking water…

Cities

Cape Town’s Foreshore Freeway Bridge has been left unfinished for…

Mapping

An interactive map highlights the shocking number of ongoing conflicts…

Mapping

Repurposed NASA maps show the racial diversity (and segregation) of…

Mapping

Benjamin Hennig maps Europe's public train networks

Mapping

A new map of global landslide susceptibility reveals vast geographical…

Deserts

For decades, scientists have been divided over how these eerily…

Forests

The first count of global tree species reveals how many…

Cities

The new ‘world’s longest flight’ now spans a distance of more…

Mountains

For the Swiss, the iconic yellow postbuses are much more…

Water

After years of inaction, could the clean-up of the Venice lagoon…

Water

Following the recent success of New Zealand’s Whanganui river, India’s…

Forests

The UN-backed REDD+ (Reducing Emissions from Deforestation and Forest Degradation)…

Mapping

Where are Europe's earthquakes located? Benjamin Hennig maps the answer