Researchers have just solved the mystery of why so many fish species evolved in Africa’s Lake Victoria region within a small timeframe. Over 700 cichlid species had evolved there within the last 150,000 years. This has long puzzled researchers because that type of evolution is very rapid and there was only one known common ancestor. As it turns out, there was more to the story—there used to be two separate ancestor fish. The details are in a paper that was just published in the journal Nature Communications.
The Cichlidae family includes a huge variety of fish found throughout the world. Some species, such as tilapia, are used for food. The cichlid family also includes many popular aquarium fish, including freshwater angelfish, oscars, discus, and blue rams. Cichlids are very diverse and come in almost every color and pattern imaginable. Most of them are found in the African Great Lakes and the continent of Africa alone has nearly 2,000 unique species. Lake Victoria, one of the Great Lakes, contains over 700 unique cichlids. All of the species evolved relatively recently and around the same time–150,000 years ago. This type of evolution is unusually fast, especially when the fish are confined to a single lake and presumably a single common ancestor.
Scientists from the around the globe collaborated to study the evolution of Lake Victoria’s cichlids. The team included researchers from Switzerland’s University of Bern, the Swiss Federal Institute of Aquatic Science and Technology, and the University of Wyoming. The team used a form of genomic analysis called restriction associated DNA (RAD) sequencing to look for possible hybridization events. They found that there wasn’t a single ancestor associated with the hundreds of evolved species—there were actually two! 150,000 years ago, there was a wet period that allowed cichlids from another region to colonize Lake Victoria. Some of the fish mated with the current species, forming hybrid fish. From there, hundreds of species rapidly evolved as the environment suddenly changed and began to dry out. The hybridization event, which would have introduced a large variety of genes, explains how so many new species could have evolved so quickly.
The team’s findings show that hybrids from two separate cichlid species from different regions led to an explosion of new cichlid species in Lake Victoria. This finally provides an explanation for the rapid evolution of cichlids and provides new insights into how hybridization events affect evolutionary rates.
Meier et al. Ancient hybridization fuels rapid cichlid fish adaptive radiations. Nature Communications (2017).