As a family, cichlids are not especially noteworthy. Cichlids are “perch-like” bony fish found all over the world and are most diverse in South America and Africa. Familiar names in the cichlid family include popular aquarium fish such as the angelfish or the discus. Cichlids such as tilapia are also commonly found in the seafood department.
Not so interesting, right?
A more interesting story looks at a subset of the cichlid family, the Lake Malawi cichlids. Lake Malawi is a geologically young lake in the Great Rift Valley of East Africa. Since it hasn’t been around for millions upon millions of years, it’s an amazing example of species colonization and adaptive radiation.
Whenever a new habitat forms, whether it be a volcanic island (like Hawaii!) or the formation of a lake (like Lake Malawi), it is initially barren of life. This is new real estate! But over time, species from neighbouring habitats will, by chance, colonize it. Plants may get blown in, or an errant current may disperse a school of fish, for example.
Due to variation in our genes, no two individuals are the same. By nature, living things tend to have preferences – some tolerate cold temperatures better, while others need more light, for example. Having preferences can be beneficial, ecologically speaking, because it prevents competition between members of a species for the same habitat. And over a LONG time, these preferences can lead to differential mating. For example, if some members of a species preferred brackish water and spent the majority of their time in brackish water, these members are more likely to mate with each other rather than someone on the other side of the lake. This is probability. And finally, over a long LONG time, genetic differences may accumulate due to this preferential mating. And so you have it – from adaptation to different environmental niches, a colonizing species can radiate into many different species, each one specialized to exploit a certain niche.
The Lake Malawi cichlids are an amazing example of this process. Species of Lake Malawi cichlids can be readily divided into groups: an open-water, sand-swelling group and a rock-dwelling group. Within these two general types, hundreds of species – each slightly different from the other – have been defined. Many more are thought to be still be undiscovered!
And, it isn’t over. Estimates have placed the origin of the Lake Malawi cichlid diversification at 10,000 years ago, or less. On a geological scale, this is nothing. Genetically, this means that there is not yet a great deal of difference between different cichlid species. As such, many different cichlid species are still able to hybridize with each other where niches overlap or when placed in a laboratory setting. Aquarists take advantage of this, for example, to breed fish with different colours and patterns.
This pattern of colonization and subsequent radiation is found repeated in many other species and habitats. Check out a few other famous examples in the silverswords of Hawaii or the finches of Galapagos!