When cichlids choose the wrong mate, it can fuel the development of a whole new species. That’s not a bad outcome for what’s usually an unfortunate mistake, and it’s one of the main reasons this colourful little fish is so exceptionally diverse, coming in a whole range of bright patterns, shapes and sizes. Usually found in the freshwater lakes of Africa, cichlids have a habit of flopping into bed with the wrong partner. When the waters are murky and the details are fuzzy, the females can accidentally introduce new genes into their population, a decade-long study on Lake Mweru in the Congo has found. “Mating between cichlids from different drainage systems produced very diverse offspring combining the genetic traits of both parental species.” In Lake Mweru, for instance, the new study turned up 40 new species. But when the lake was first formed, about a million years ago, this body of water only contained cichlid lineages from the Congo and the Zambezi. Further, DNA analysis revealed these new fish came from a mix of both ancestors. Many cichlids alive today have evolved only recently, meaning in the past million years or so. In Lake Malawi, for example, more than have descended from the original cichlids that lived there up to 2 million years ago. And in Lake Victoria, there are more than of cichlid that have all evolved in the last 150,000 years. This rapid case of evolution has produced many distinct species that are genetically compatible, meaning they can produce viable and fertile hybrid offspring. As a result, some researchers argue that hybridisation is what has led to such great cichlid diversity. Testing this in the lab, researchers found that when cichlids mate, the females are in charge. But sometimes, when the light is dim or the male has similar colourings, the bachelorette can make the wrong choice. The authors suspect this is probably what happened all those million years ago, when the original lineages of cichlids came face to face in a newly-formed lake.
The study was published in Nature Communications.