The age of Lake Victoria is just 16,000 years, but within this time frame, around 500 various species of cichlid fish have evolved here, primarily due to hybrids born from inter-species breeding. Scientists at the University of Bern, the University of Cambridge, and the Wellcome Sanger Institute found that these diverse species had evolved from three lineages of cichlid that arrived in Lake Victoria about 16,000 years ago. This rapid evolution is unusual as it typically takes over a million years for a new species to evolve.”They evolved from probably three lineages that came together in the lake, hybridized, combined their genetic variation, and generated this huge diversity of hybrids, which then evolved into different species,” said Dr. Joana Meier, the study’s first author and group leader at the Wellcome Sanger Institute.
“We now find over 500 species of cichlid fishes. We found out that all those cichlid fish species actually evolved within the lake in just 16,000 years, which is absolutely crazy. Usually, it takes over a million years for a new species to evolve,” Dr. Meier added.
The cichlids have thrived in Lake Victoria and occupy almost every imaginable niche in the ecosystem, displaying a variety of shapes, sizes, colors, and forms. “The species are super different too. Some are algae scrapers, others eat zooplankton, and others are top predators that eat other fish,” explained Dr. Meier.
The team believes this rapid evolution occurred because the lake’s water was initially very murky, hindering the cichlids from identifying different species and leading to a festival of hybridization. The success of cichlid hybridization in Lake Victoria challenges the assumption that two different species cannot reproduce and create viable or fertile offspring.
As opposed to hybrids always being an evolutionary dead-end, it is possible for them to become a positive force in the survival of a gene. Many hybrids born to parents of different species won’t be successful and might even be infertile. However, for a lucky few, the combination of genes could provide them with an advantage over their peers, helping them to survive and reproduce.
This phenomenon is not limited to cichlids in Lake Victoria. Introgressive hybridization within the genome of most living animals, from butterflies and spiders to marine mammals, is evident with the use of new genomic technologies to sequence DNA. The human genome also shows genetic evidence of Homo sapiens breeding with Neanderthals and Denisovans, two other species of hominin that are now extinct.
The study challenges the idea that hybridization always results in a genetic dead-end. “Under certain circumstances, some hybrids may actually be doing better. It’s possible that in most circumstances they are not, but in some, they are,” according to Meier.
The study is published in the journal Science. An earlier version of this article was published in October 2023.
