Deep drilling in Europe's oldest lake sparks new evolutionary insights

Drilling in Lake Ohrid feels like travelling back in time. The 1.4-million-year-old lake on the border between Albania and North Macedonia is Europe's oldest. Data from sediment cores suggest that the older and more stable an ecosystem is, the longer-lived its species and the more stable its species communities.

What determines species diversity? That's "one of the fundamental questions in biology", writes an international research team that includes Aleksandra Cvetkoska from NIOO-KNAW and Utrecht University in the leading scientific journal Science Advances.

To answer the question, high-resolution empirical data are needed that directly track diversity over time. Such data have been notioriously scarce, but Lake Ohrid presents a unique opportunity. It's not only Europe's oldest freshwater lake but also its most species-rich. The lake boasts 300 'endemic' species, i.e. species that are found nowhere else.

New species

The team led by scientists from the Justus Liebig University Giessen and the University of Cologne combined the environmental and climate data of a 568-meter-long sediment core with fossil records of over 150 endemic diatom species. Diatoms - algae found in oceans, waterways and soils - are the lake's most biodiverse species group.

The data show that after the formation of the lake, new species emerged within a few thousand years. However, many of them died out again very quickly. This is due to the fact that young, small and shallow lakes are particularly sensitive to environmental changes, including fluctuations in temperature, lake level and nutrients.

When the lake became deeper and larger, it stopped being at the mercy of changes in environment and climate. Consequently, both speciation and extinction processes slowed down dramatically.

Unique insights

The researchers attribute this trend to several factors: fewer new habitats emerging, limits to species diversity that are environmentally defined, and increased environmental and climate buffering.

These factors resulted in an evolutionary shift from a volatile assemblage of evolutionarily short-lived species to a stable community of long-lived species. That stable community still exists today, including a striking number of species that are only found in Lake Ohrid.

The insights from the drilling programme provide a new understanding of the evolutionary dynamics in ecosystems, concludes Aleksandra Cvetkoska: "The unique dataset from the lake is one of the first of its kind. Its unprecedented diversity in combination with the length of the record makes it truly special."

Future research

Cvetkoska believes the data from Lake Ohrid "can be used as a test case of different evolutionary concepts and models". The data also underline the crucial role of ecosystem buffering for mitigating the effects of environmental and climate dynamics.

For future biodiversity research, these findings could hold great significance.

(Photograph of Lake Ohrid: David Stanek/Flickr)

• Scientific article: Thomas Wilke, Torsten Hauffe, Elena Jovanovska, Aleksandra Cvetkoska, Timme Donders et al., 'Deep drilling reveals massive shifts in evolutionary dynamics after formation of ancient ecosystem', Sciences Advances Vol 6, No. 40, doi.org/10.1126/sciadv.abb2943.
• Utrecht University: Deep drilling in Europe's oldest and most species-rich lake provides new insights into evolution.