Evolution research in Ohrid: The secret in Europe's oldest lake
Lake Ohrid, Europe's oldest lake, lies between Macedonia and Albania. The deposits at its bottom are a unique climate archive. They show how new species arise - and then disappear again.
If you look down at the shimmering Lake Ohrid from the heights of the Galičica National Park, you can imagine for a moment that there are no hotels and restaurants, no shopping markets and factories. You can, at least for a moment, get a feeling for what it was like when the border region between Macedonia and Albania was deserted.
People have settled on the shores of the lake for about 6500 years, but the water has a much, much longer history. "The Ohrid lake is the oldest lake in Europe. It has existed for 1.36 million years without interruption," says geographer Bernd Wagner from the University of Cologne. "It's unique that we can track an ecosystem over such a long period of time."
For comparison, the age of the waters in Germany: Lake Constance, Müritz and others mostly emerged after the last ice age around 10,000 years ago when the glaciers melted. Only the Maar of the Eiffel are partly a bit older.
Lake Ohrid is a member of a rather exclusive club, that of the oldest lakes on earth. Lake Baikal, Tanganyika and Titicaca also belong to it. Together with colleagues, Wagner evaluated a 565 meter long sediment core with deposits from the bottom of the body of water. The samples are a unique archive for the development of the climate in the Mediterranean region. However, as the team now reports in the journal "Science Advances", they also allow a look into a unique laboratory of life.
"There are many endemic species that can only be found here," says evolutionary biologist Thomas Wilke from the University of Giessen. And whoever examines these species more closely, who studies their becoming and disappearing, can watch evolution at work.
He can see how long it takes for a new species to form in a new habitat and analyze their competition for habitat and food. And he can determine when and why they eventually disappear again. All of this information can be found in the innumerable layers of the sediment core, the oldest at the bottom and the youngest at the top. "The drill core is a picture book of the history of the lake," says Wilke.
The researchers know about 200 species that are unique to Lake Ohrid. The best known is the Ohrid trout, which is around 60 centimeters long and marked with colorful spots. Above all, Wilke and his colleagues had eyes for the much smaller lake inhabitants that can be found in the sediment: diatoms. The team was able to detect more than 150 different species of these so-called diatoms.
The diatoms have a hard shell made of silicon dioxide. And it is quite indestructible, which is why some of the specimens in the sediment survived many hundreds of thousands of years undamaged. Depending on their type, they show characteristic shapes and structures under the microscope. These individual characteristics helped the researchers to understand the time periods in which new species emerged in the lake - and when they finally became extinct again.
The new research overturns a paradigm of evolutionary researchers. Up until now, says Wilke, the following situation has been assumed: If a new habitat is created anywhere in the world, the formation rate of new species is high at the beginning because all species can still find a suitable habitat. In contrast, the rate of extinction, according to previous opinion, is very low at the beginning. "But it looks completely different," says Wilke, summarizing the findings from Lake Ohrid.
The analysis of the sediment showed that there were high rates of extinction even at the beginning of life in the lake. The evolutionary biologist explains that many species have found an ecological niche where competition was low. Often enough, however, this was unsuitable - and the species finally disappeared. Only gradually did the lake calm down: "In the beginning, many species only existed for a few thousand years," says Wilke. "But now there are millions." The lake's ecosystem has become stable over time.
More interesting than the Galápagos for evolutionary research
But what is the point if you know the speciation rates of algae in a lake in the Balkans? The researchers say that it can also be used to study the fate of other species in other parts of the world. "You'd think that such small algae come and go," says Wilke. "But the periods of time in which species of diatoms appear and disappear again are comparable to those of mammals." The researcher says that the diatoms from Lake Ohrid are "good models for evolution".
With the help of the tiny diatoms, one can even learn more about the development of the species than, for example, on the Galápagos Islands, which have been known for this since Charles Darwin, says Wilke. On the one hand, there are significantly more species in Lake Ohrid that are only found there. The larger sample makes the scientific analysis much more precise. On the other hand, the fossils of the diatoms are perfectly preserved in the sediment core. Of the species on the Galápagos, lizards and birds, fossil remains are largely missing.
At Lake Ohrid, you can see an example of what makes a stable ecosystem, says Wilke. After the turbulent early days, the communities remained amazingly stable, even if environmental factors had changed. Warm times and cold times came and went - and life went on. The species had found their place somewhere in deep lake water and had little to compete with each other. So they could withstand external stress comparatively well.
