Researchers have discovered a powerful genetic mechanism that may help explain how some species evolve at surprising rates. Certain parts of the DNA, known as “flipping” segments, appear to help fish quickly adapt to new environments or split into entirely new species. These genetic traits act like evolutionary accelerators, conserving useful traits and accelerating change.
One of biology’s biggest questions is how Earth came to be home to such a wide range of plants and animals. The cichlids of Lake Malawi, located in East Africa, are a notable example. In this single lake, more than 800 species emerged from a common ancestor in a much shorter period of time than it took humans and chimpanzees to diverge.
What’s even more remarkable is that all of this diversification occurred within the same body of water. Some cichlids evolved to be predators, while others specialized in eating algae, sifting sand, and eating plankton. Each species has established its own ecological role while coexisting.
Scientists from the University of Cambridge and the University of Antwerp set out to understand how this rapid evolution was possible. Their findings were published in the magazine science.
Discovery of inverted DNA segments
Researchers analyzed the DNA of more than 1,300 cichlids for their study. They were looking for genetic traits that could explain the unusual pace of evolution.
“We found that in some species, large chunks of DNA on five chromosomes are inverted, a type of mutation called a chromosomal inversion,” said lead author Hennes Svardal from the University of Antwerp.
Under normal conditions, reproduction involves recombination, a process in which DNA from both parents is mixed. However, within these inversion regions, this mixing is blocked. As a result, groups of genes remain connected and passed intact from generation to generation. This preserves already beneficial combinations of traits and allows evolution to proceed more efficiently.
“This is like a toolbox with all the most useful tools packed together, storing good genetic combinations that help fish adapt to different environments,” said lead author Moritz Blumer from the Cambridge Department of Genetics.
“Supergenes” and rapid adaptation
These linked gene clusters are often called “supergenes.” In cichlids, it appears to play a major role in shaping species differences. Although different species can still interbreed, these inversions limit the amount of DNA mixing and help maintain different traits.
This is especially important in areas where species overlap, such as the open sands of lakes where there are no clear physical boundaries separating habitats.
Many of the genes within these supergenes influence traits essential for survival and reproduction, such as vision, hearing, and behavior. For example, fish that live in deep water (200 meters deep) have to deal with lower light, higher pressure, and different food sources compared to fish closer to the surface. Those supergenes help maintain the specific adaptations needed for those conditions.
“When different cichlid species interbreed, complete inversions are passed on between them, resulting in important survival traits such as adaptation to specific environments and accelerating the evolutionary process,” Bloomer said.
A broader role in evolution
Chromosomal inversions do more than just preserve beneficial traits. They also function as sex chromosomes and can influence whether an individual develops as a man or a woman. Sex determination plays a role in the formation of species, adding a new layer to our understanding of evolution.
“Although our study focused on cichlids, chromosomal inversions are not unique to cichlids,” said co-senior author Professor Richard Durbin, from the University of Cambridge’s Department of Genetics. “They are also found in many other animals, including humans, and are increasingly considered to be important components of evolution and biodiversity.”
Researchers believe these discoveries could help answer long-standing questions about how life can diversify so rapidly under the right conditions.
“We have been studying the process of speciation for a long time,” Svardal said. “By understanding how these supergenes evolve and spread, we are moving closer to answering one of science’s great questions: How does life on Earth become so rich and diverse?”
