More than 500 species of fish undergo rapid evolution in a single lake through hybridization

TToday, Lake Victoria is relatively young at only 16,000 years old, but during that small time frame, about 500 different species of cichlids have managed to evolve here. Remarkably, this explosion in diversity is primarily due to the hybrids generated as a result Interspecies breeding.

In one study, scientists at the University of Bern, the University of Cambridge, and the Wellcome Sanger Institute discovered that hundreds of completely different species had in fact all evolved from just three strains of tilapia that arrived in Lake Victoria – the largest lake in Africa. Lake – about 16,000 years ago when it was refilled after a severe drought. This is incredibly fast in terms of development.

“It evolved from probably three lineages that got together in the lake, hybridized, combined their genetic diversity, and produced this huge diversity of hybrids, which then evolved into different species.” Dr. Joanna MayerThe study's first author and group leader at the Wellcome Sanger Institute told IFLScience.

“We now find over 500 species of cichlids. We discovered that all the cichlid species actually evolved within the lake in just 16,000 years, which is absolutely crazy. “It usually takes more than a million years for a new species to evolve,” added Dr. Mayer. .

“It's like a rabbit turning into a wolf in the blink of an eye. Very crazy environmental differentiation – very, very fast.

From their humble beginnings, cichlids now thrive in Lake Victoria and occupy almost every imaginable niche in the ecosystem. They also appear different to view, and are characterized by a variety of different shapes, sizes, colors and shapes.

“The species are also very different. Some are algae scrapers, others eat zooplankton, and others are top predators that eat other fish,” Dr. Mayer explained.

The team believes this amazing situation occurred because the lake's water was very turbid when it was first refilled. This meant that the cichlids were unable to tell each other's colors and had difficulty identifying different species. The hybridization festival was held in the middle of muddy waters.

The success of cichlid hybridization in Lake Victoria challenges one of the oldest assumptions about evolution that two different species cannot reproduce and create viable or fertile offspring. Unlike hybrids always being an evolutionary dead end, they can become a positive force in the gene's survival.

Many hybrids born to parents of different species will not be successful and may be sterile. However, for a lucky few, the gene pool can provide them with an advantage over their peers, helping them survive and reproduce.

“They generate a lot of genetic diversity. Even if some of them do very poorly, it still helps if some of them do well,” Mayer told IFLScience.

This doesn't just apply to Lake Victoria's cichlids either. If you look around, you'll be able to see glimpses of inbreeding within the genomes of most living animals, from butterflies and spiders to marine mammals.

“With new genomic techniques for DNA sequencing, we now see that all species – including humans – have some parts of their DNA derived from another species, suggesting that there was hybridization in the past,” Mayer explained.

In fact, if you look at the genomes of many modern humans, you can find genetic evidence of this Homo sapiens Breeding with both Neanderthals and Denisovans, two other hominin species that have since become extinct.

For better or worse, humans are also the product of hybridization. In the case of some people living in East Asia, there is evidence that Denisovan DNA helped them adapt to higher altitudes. On the other hand, Neanderthal DNA in the genome of people from Europe could increase the risk of developing some diseases, including Covid-19 and depression.

The study challenges the idea that hybridization always ends in a genetic dead end. “Under certain conditions, some hybrids may actually perform better. It may not be the case in most circumstances, but sometimes it is,” Mayer said.

The study is published in the journal Sciences.

A previous version of this article was published in October 2023.