Scientists discover a new way to create species

DNA Genetics Evolution Concept Art

The scientists were able to learn how the new species has evolved by using morphometry, stable isotope analysis, and genome sequencing.

The team of an evolutionary biologist has found a new type of speciation.

The evolution of a new species by hybridization of two previously described species with no change in chromosome number is very unusual in the animal world. So far, there are only a few empirically recognized cases of this spontaneous mode of evolution (from one generation to the next) known as homoploid hybridization.

A study led by Axel Meyer, professor of Zoology and Evolutionary Biology at the University of Konstanz, has successfully demonstrated the appearance of a new hybrid species in cichlid fish. This is probably the first instance of this method of genetic speciation in vertebrates. Researchers reveal that a new hybrid species of the cichlid has emerged to arrows Y A. xyloaensis in the crater of Lake Xiloá in Nicaragua using whole genome sequencing of more than 120 individuals, as well as a number of other techniques.

Their findings were recently published in the journal

Cichlids in Nicaragua

Cichlids (here Amphilophus xiloaensis) from the crater lake Xiloá in Nicaragua. Credit: Ad Konings; Cichlid Press

The majority of fishes reproduce among themselves

The study team was also able to discover that the majority of individuals of the new species reproduced solely among themselves due to the detail of the markings, indicating that it is indeed a new species. It is also plausible that hybrids developed as a result of a “mistake” in mate selection, which would explain why their offspring could prove infertile or hybrid animals that mate with one of the two parent species again (“backcrossing”).

The new, very young species, emerging within a few hundred generations, is not directly intermediate between the two parent species, A. sagittae and A. xiloaensis, neither morphologically, physiologically, nor ecologically. Instead, the hybrids show aspects of a transgressive phenotype with traits not found in either parent species. As a result, they occupy a different ecological niche than their two parent species, allowing them to coexist in the lake.

Ecological consequences from the physique

The fishes differ from their ancestors in the shape of their caudal root – the part of the body where the tail fin attaches. “Possibly that is why they are better swimmers. You find this type of body proportion often in fish that can accelerate very quickly”, Meyer explains. This allows the hybrids to roam different feeding grounds than the other four species in lake Xiloá, including both parental species, of which one is an elongated species living in open water, while the other has a deeper-bodied shape and lives close to the shore.

With stable isotope analysis of the animals, the researchers were able to show that the prey of the new species consists of other fish, crabs, and shrimp – prey that is already very high on the food chain. Probably the individuals of the new species are the most successful predators of the lake.

Unique ecological niche

The new hybrid species occupies a unique ecological niche, which is very important in a small ecosystem like Lake Xiloá, whose diameter is only a little more than one kilometer. “The prerequisite for individual species coexisting for long periods of time in such a limited habitat is that they are no competition for each other”, says Axel Meyer. Especially since the new speciation does not occur over a large geographic distance, but under sympatric conditions within the same small habitat as that of the original species.

Genome sequencing, morphometrics, stable isotope analysis – with this combination of different data sets, the researchers were able to understand how the new species has evolved. In a new study, the researchers examine how often errors occur when hybrid fishes are given the choice of reproducing with each other or with individuals of their parent species.
Finally, the question is: How is mate choice controlled genetically?

Reference: “Early stages of sympatric homoploid hybrid speciation in crater lake cichlid fishes” by Melisa Olave, Alexander Nater, Andreas F. Kautt and Axel Meyer, 6 October 2022, Nature Communications.
DOI: 10.1038/s41467-022-33319-4

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