Arctic vs Antarctic lake microbes: new research reveals unique evolutionary tales

High Arctic (left) and Continental Antarctic (right) lake bottoms, covered by dense microbial mats.  Credits: David Velazquez (image left), Sakae Kudoh (image right) (large view)

High Arctic (left) and Continental Antarctic (right) lake bottoms, covered by dense microbial mats. Credits: David Velazquez (image left), Sakae Kudoh (image right)

(06-12-2023) An international research team of scientists led by biologists from Ghent University investigated the biodiversity and evolutionary history of microorganisms in Arctic, sub-Antarctic and Antarctic lakes in the first large scale study using DNA.

The polar regions are characterized by extreme living conditions such as very low temperatures and low availability of water and nutrients. Lakes in this harsh environment are oases of biodiversity and productivity, where life is dominated by microscopic organisms. For a long time it was assumed that microorganisms, because of their astronomical numbers and small cell size, have moved unhindered across the Earth and colonized all suitable habitats. This hypothesis has now been tested by using DNA to compare the composition of these communities in more than 200 Arctic, sub-Antarctic and Antarctic lakes to determine whether they have the same evolutionary history.

Antarctica has gradually been covered by an ice sheet since the Late Eocene (34 million years ago), which has led to the extinction of most groups of plants and animals, and is also highly isolated in the Southern Hemisphere, which has prevented these groups from recolonizing the continent. Arctic landmasses, on the other hand, are geographically highly connected and were only covered extensively by ice sheets during glacial maxima. In animals and plants, this has led to strong differences in the evolutionary history of species and their geographical distribution at both poles. According to the current hypothesis, this would not be the case for micro-organisms which were thought to move freely across the Earth.

DNA has revealed a distinct evolutionary history between the Arctic and Antarctic

What is striking is the large difference in the composition of the microbial communities between the polar regions, with lakes at the North and South Poles being dominated by different groups. Heterotrophic bacteria and grazing-resistant diatoms appear to be relatively more abundant in the Arctic, while cyanobacteria and green algae are more dominant in Antarctic lakes. Species diversity is also lower in Antarctica.

The analyses showed that the formation of ice caps 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 subspecies and varieties 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 is rather limited, and that the Southern Ocean also forms a major barrier for microorganisms.

"The unique character of the microbial communities in these polar lakes is a strong argument for better protecting these habitats against human influence through, among other things, increasing tourist exploitation of Antarctica", says Bjorn Tytgat