The first large-scale DNA study of microorganisms in Arctic, sub-Antarctic and Antarctic lakes has revealed their distinct evolutionary histories, dispelling long held beliefs that these microorganisms are the same all over the world.
The collaborative research, led by biologists from Ghent University in Belgium and including SAEF Director, Professor Steven Chown, was published in the journal Science Advances.
“We know polar bears are only found in the Arctic and penguins in the Antarctic because of their unique evolutionary histories,” Professor Steven Chown said.
“For many years scientists mistakenly thought that due to their small size and huge numbers, microorganisms were able to spread freely across the Earth and colonize suitable habitats while remaining largely the same.”
“But our research shows that like the differences between Arctic and Antarctic animals, lake microorganisms in each polar region are quite different and that this has been driven by past climate change and extinction events.”
The polar regions are characterized by extreme living conditions such as freezing temperatures and low availability of water and nutrients. Lakes in these harsh environments are oases of biodiversity and productivity, where life is dominated by microscopic organisms.
Until the Late Eocene (34 million years ago), Antarctica was had much more extensive vegetation. As the climate changed, it was gradually covered by an ice sheet, which led to the extinction of most groups of plants and animals.
Arctic landmasses, on the other hand, are highly connected geographically and have only been extensively covered by ice sheets during glacial maxima.
In animals and plants at both poles, this has led to strong differences in the evolutionary history of species and their geographical distribution.
However, for decades scientists have believed that this was not the case for microorganisms which were thought to move freely across the Earth.
To test this hypothesis, the team used DNA to compare the composition of the communities of microorganisms in more than 200 Arctic, sub-Antarctic and Antarctic lakes. The analysis revealed that like Arctic versus Antarctic animals, microorganisms from each pole have their own distinct evolutionary history.
The team found large differences in the composition of the microbial communities in each polar region, with lakes being dominated by different groups.
Heterotrophic bacteria and grazing-resistant diatoms appear to be more abundant in the Arctic, while cyanobacteria and green algae are more dominant in the Antarctic. Overall species diversity is lower in Antarctica.
The analyses showed that the formation of the ice sheets also caused several groups of microbial organisms to disappear from Antarctica.
The researchers were able to demonstrate that the groups that did survive could evolve in isolation. In this way, a common ancestor species gave rise to several groups with a distribution restricted to Antarctica.
Furthermore, even at deep evolutionary levels, it appears that many genetic lineages are long-standing and unique to Antarctica. This shows that movement over long timescales has been limited, and that the Southern Ocean forms a major barrier to this movement.
The unique characteristics of the microbial communities in these polar lakes underscores the need for to better protect these habitats against human influence.
Tytgat, B., Verleyen, E., Sweetlove, M., Van den Berge, K., Pinseel, E., Hodgson, D.A., Chown, S.L., Sabbe, K., Wilmotte, A., Willems, A., The Polar Lake Sampling Consortium & Vyverman, W. 2023. Polar lake microbiomes have distinct evolutionary histories. Science Advances. 9, eade7310. https://doi.org/10.1126/sciadv.ade7130