Cradle of fish

Freiburg biologist Dr. Kristin Kaschner, evolutionary biologist Dr. Daniel Rabosky of the University of Michigan, USA, and Cristina Garilao, a biologist from GEOMAR - Helmholtz Centre for Ocean Research Kiel have been working with an international team of researchers on a major study into the evolutionary relationship of more than 30,000 fish species. They arrived at the surprising conclusion that over the past few million years, cold-water marine fish - such as those living in the Arctic Ocean - formed new species twice as fast as tropical fish. Their study has been published in the journal Nature.

Tropical seas are home to many different species of fishes, more than in the cold oceans at higher latitudes. One of the usual explanations for this was that the warm environment of a reef was an evolutionary hot spot where especially large numbers of species could develop. Biologist called the phenomenon by which the biodiversity of a region depends on its latitude, “latitudinal diversity gradient.”

Researchers from a total of eight institutions investigated the relationship between latitude, the number of species, and the rate at which new species evolve, for marine fishes. For this they used a combination of genetic investigative methods and predictive models for geographical distribution. “Our results are surprising and unexpected, because the rate of species evolution was fastest in the regions with the lowest number of species” says Kristin Kaschner. The general expectation is that a high rate of development of new species is among the factors leading to a high level of biodiversity. However this depends in turn on how many species survive and how many die out. However the researchers were not able to assess the extinction rate with the methods used in this study. “We’re now using both fossils and new statistical tools to try to get a handle on what extinction might have been doing in both the polar regions and the tropics,” says Rabosky, the study’s lead author.

In their analysis, the team made use of information provided by AquaMaps - a data base with maps of the global distribution of marine animals - more than 25,000 of them - from mammals, fish, and turtles to algaes, mollusks, and corals. Kristin Kaschner of Freiburg’s department of Biometrics and Environmental Systems helped to develop the information system, working with researchers from GEOMAR – Helmholtz Centre for Ocean Research Kiel.

Publication:
Daniel L. Rabosky, Jonathan Chang, Pascal O. Title, Peter F. Cowman, Lauren Sallan, Matt Friedman, Kristin Kaschner, Cristina Garilao, Thomas J. Near, Marta Coll, Michael E. Alfaro: An inverse latitudinal gradient in speciation rate for marine fishes. In: Nature. https://www.nature.com/articles/s41586-018-0273-1

AquaMaps article in the University of Freiburg online magazine 

AquaMaps database