• Organism

Cichlids

Cichlids are a dazzling group of fish which have undergone an evolutionary explosion in the last few million years.

Overview.

Status: Least concern

Scientific name: Astatotilapia burtoni

Length: 6 inch

Habitat: Slow, flowing freshwater bodies: rivers, lakes, marshes, swamps

Diet: Omnivorous - insect larvae, small fish, algae, plants

Cichlids can be found worldwide, from African river species such as the Nile tilapia to lake-dwelling species spread throughout South Asia, Africa and South America. Perhaps the most famous are the East African cichlids, which have exploded into a kaleidoscope of colours and shapes while filling a vast range of habitats in just a few million years. In lake Malawi thousands of species of cichlids can be found, while their cousins in lake Tanganyika and lake Victoria show surprisingly similar adaptations to comparable habitats and food sources - from predators living close to the surface through to algae grazers occupying the murky depths.

The extraordinary range of colours and shapes in cichlid fish has rendered them a popular addition to aquariums worldwide, but they’re of far greater importance than the mere pleasure that is to be derived from their glamorous appearance. The Nile tilapia has become an economic and food security powerhouse, occupying fish farms throughout the tropics. For scientists, especially those at EI, they have been a beacon for understanding the mechanisms of evolution that allow organisms to adapt so rapidly and successfully to a host of different environments.

Scientific significance.

Cichlids are a fantastic model system for comparative genomics research (comparing the genomes of different species). The thousands of species of cichlid fish in the East African lakes all derived from a single ancestral species millions of years ago, which means by comparing all of the different species we now see we can understand the process known as adaptive radiation - the evolutionary explosion to fill different biological niches we have already mentioned.

Rapid Evolution

Recent research at the Earlham Institute has shed important light on many different genetic factors guiding this evolution, from hybridization through to large-scale genetic rewiring of the genes important for adaptive traits, like vision. It shows how evolution can happen very rapidly, and that genomes can be incredibly plastic. The gradual genetic drift of mutations over long periods of time is just one part of a colourful story.

Understanding the mechanisms of evolution such as this can, perhaps surprisingly, be applied to understanding our own evolution - for what we discover tells a story of our shared ancestry and subsequent divergence. A more practical reason, in the short term, to study cichlids is that they are a prized food source and a potential avenue towards food security and socio-economic stability for people in some of the world’s most impoverished regions. Research into the genetics of cichlid fish can inform local breeding programmes, highlighting genes which aid local adaptation and boosting breeding efforts to maximise production. Simultaneously, as we will see in the conservation section, we can use this information to protect wild fish - by preventing them crossbreeding with introduced, farmed species.

Conservation.

Although tilapia farming promises much in terms of food security, there is a constant battle to keep farms productive while protecting native biodiversity. Escaped fish - usually Nile tilapia - have been shown by EI scientists to quickly hybridise with native species. That means the biodiversity of lakes and rivers can be put under strain. For fish farmers, hybridisation also means that farmed fish can lose vigour and fertility, meaning that aquaculture systems become less productive.

EI scientists are therefore working on a number of projects - from quick DNA testing through to developing machine learning apps - to help prevent this sort of hybridisation, to boost fish farming while protecting biodiversity.

What Earlham Institute is doing.

EI scientists have long-standing collaborations with organisations and institutes such as WorldFish, Bangor University, University of Hull, University of Basel, University of Bristol, Wisconsin Institute for Discovery and the University of Rothamsted, who are together applying expertise in genomics and bioinformatics to aid aquaculture efforts in East Africa.

Recent discoveries show how large scale genome rearrangements could have contributed to cichlid evolution, as well as how more recent hybridization events have occurred between native and farmed tilapia. Another study of five different tilapia species shows that genetic rewiring - small modifications to the regulatory regions of DNA - potentially plays a powerful role in driving cichlid evolution, particularly with regard to vision.