How “Supergenes” Help Fish Evolve into New Species
Cichlid fish research helps an international research team led by the University of Antwerp to unlock the secret of biological diversity
Why are there so many different kinds of animals and plants on Earth? One of biology’s big questions is how new species arise and how nature’s incredible diversity comes to be. A new paper published in Science <ref> by an international team led by researchers at the University of Antwerp and the University of Cambridge takes us one step closer to the answer.
Cichlid fish from Lake Malawi in East Africa offer a fascinating clue. In this single lake, over 800 different cichlid species have evolved from a common ancestor in just a fraction of the time that separates humans from chimpanzees. What’s even more remarkable is that this explosive diversification happened without physical barriers — all in the same body of water. Some of these fish became large predators, others adapted to eat algae, sift through sand, or feed on plankton. Each species found its own ecological niche.
So how did this happen so fast? In their research, senior author Hannes Svardal from the University of Antwerp and his colleagues looked at the cichlids’ DNA to see if there’s something special about their genes that might explain this rapid evolution. “We discovered that, in some species, large chunks of DNA on five chromosomes are flipped — a type of mutation called a chromosomal inversion.”
Keeping species separate
Normally, when animals reproduce, their DNA gets reshuffled in a process called recombination — mixing the genetic material from both parents. But when one chromosome is flipped, this mixing is blocked in that region. This means certain gene combinations can be passed down intact, generation after generation. These preserved blocks of genes are sometimes called “supergenes”.
One common ancestor evolved into more than 800 cichlid species.
In Malawi cichlids, these supergenes seem to play several important roles. Although cichlid species can still interbreed, the flipped DNA helps keep species separate by preventing their genes from blending too much. This is especially useful in parts of the lake where fish live side by side — like in open sandy areas where there’s no physical separation between habitats.
Key factor in evolution
Interestingly, the genes inside these supergenes often control traits that are key for survival and reproduction — such as vision, hearing, and behaviour. For example, fish living deep in the lake (down to 200 meters!) need different visual abilities than those near the surface. These supergenes help maintain those special adaptations. First author Moritz Blumer, postgraduate student at the University of Cambridge, noted “We found instances where transfer of whole inversions between species by hybridisation appears to have transferred particular ecological adaptations.”
Another fascinating detail, as noted by co-first author Valentina Burskaia from the University of Antwerp was that "in some cases, these flipped regions now act as sex chromosomes, helping determine whether a fish becomes male or female. Since sex chromosomes can influence how new species form, this opens exciting new questions about how evolution works.”
Hannes Svardal (left) prepares for a dive in Lake Malawi.
“While the study focused on cichlids, chromosomal inversions aren’t unique to them. They’re also found in many other animals — including humans — and are increasingly seen as a key factor in evolution and biodiversity.” commented Professor Richard Durbin, co-senior author from the University of Cambridge.
Professor Svardal concluded “We have been studying the process of speciation for a long time. Now, by understanding how these supergenes evolve and spread, we’re getting closer to answering one of science’s biggest questions: how life on Earth becomes so rich and varied.”