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A fundamental question in evolutionary research is: Is a geographic barrier necessary for the emergence of new species that divides an original population into two genetically separate populations? Or, on the other hand, is a so-called sympatric speciation possible - the evolutionary divergence of a population in the same geographical area? Only very few examples of sympatric speciation are known worldwide, even these are not undisputed. Evolutionary biologists from Constance have now completed the most detailed study of sympatric speciation to date. Using around 20,000 genetic traits from 450 fish, they documented the parallel evolution of cichlids in the Nicaraguan crater lakes Apoyo and Xiloá. The work of the biologists around Prof. Axel Meyer, Ph.D., and Dr. Andreas Kautt allows conclusions to be drawn about possible evolutionary mechanisms of sympatric speciation. At the same time, the scientists underpinned the empirical evidence for a much-noticed preliminary work by Axel Meyer on the sympatric speciation of these cichlids, which was published in 2006 in the science journal Nature. The latest research results are published in the June 30, 2016 issue of PLOS Genetics.

The cichlids of the volcanic crater lakes Apoyo and Xiloá in Nicaragua are one of the rare examples of sympatric speciation. In only around 800 generations - a period of estimated 1,000 to 1,500 years - a fish population has evolved into four to five different species, although the fish lived together in the same geographically isolated lake for the entire time. The Konstanz evolutionary biologist Axel Meyer described this astonishing evolutionary phenomenon in 2006 in the science journal Nature. Together with Andreas Kautt, he has now broken down the genetic family tree of the fish populations in detail.

“Our data suggest that there was a second wave of colonization just before the split into two types,” explains Andreas Kautt. Accordingly, a second group of the same cichlid species ended up in the crater lake. The biologists suspect that this second wave of colonization refreshed the cichlid's gene pool and was the decisive factor in the process of dividing them into two species.

In evolution research, three models for sympatric and supposed sympatric speciation are known. The first model, the “purest form” of sympatric speciation, describes the development of two species from a common population. In the second model, two or more waves of colonization of a habitat by the same species take place before splitting into two species. According to this scenario, sympatric speciation is preceded by the formation of a swarm from several population waves of the same ancestral line - and consequently a refreshment of the gene pool. “Our data suggest that speciation in the crater lakes Apoyo and Xiloá took place in this way. The second wave of colonization was integrated into the gene pool of the crater lake population before the evolutionary split took place. The process of splitting into two types then took place without geographical barriers, ”explains Andreas Kautt.

The third model, which is very difficult to distinguish and which is often cited as an objection by critics, describes an alleged sympatric speciation. This scenario also assumes a second population wave. However, the first population of the crater lake had already developed further before the second population wave was added. At the time of their meeting, the two swarms from the same ancestral line were already separate species. In this scenario there would be no real sympatric speciation because a geographic barrier at the time of the divergence played a role. However, based on the genetic analysis, the evolutionary biologists from Constance were able to rule out this case: The genetic pedigrees of the fish show that the split into two species did not take place until after the second population wave. The geneticists thus provided empirical evidence for sympatric speciation in the Nicaraguan crater lakes Apoyo and Xiloá.

The research project was part of Axel Meyer's ERC Advanced Grant “Comparative genomics of parallel evolution in repeated adaptive radiations”. In 2011, the European Research Council (ERC) awarded Axel Meyer this renowned science prize for research into parallel evolution. The scientific work on the crater lakes of Nicaragua is to be deepened in the coming years. Among other things, the evolutionary biologists from Konstanz are planning a complete sequencing of the genomes of the fish populations.

Original publication: Kautt AF, Machado-Schiaffino G, Meyer A (2016) Multispecies Outcomes of Sympatric Speciation after Admixture with the Source Population in Two Radiations of Nicaraguan Crater Lake Cichlids. PLoS Genetics 12 (6): e1006157. doi: 10.1371 / journal.pgen.1006157

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Dr. Andreas Kautt
University of Konstanz
Department of Biology
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78464 Constance
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