Two important concepts in evolutionary biology, mutualism and altruism, were first made famous by the colorful anarchist prince Peter Kropotkin. He argued that cooperation could be an equally powerful driver of evolution as competition. Crucially, he was inspired by his youth as a geographer in the Russian Far East, where he observed how in particular the harsh climate favored cooperation, both within and between species.
Now, researchers have shown that previously unknown apparent mutualisms allow biodiversity to flourish to an unexpected degree in an even more extreme habitat: weathered debris in front of a glacier in Antarctica. The study is published in Frontiers in Microbiology .
"Here we reveal unexpectedly abundant and diverse microbial community even in these driest, coldest, and nutrient-poorest of soils, which suggest that biodiversity estimates in Antarctic soils may be greatly underestimated," said Dr Dirk Wagner, a professor at the GFZ Helmholtz Centre for Geosciences and the University of Potsdam in Germany, and the corresponding author.
"Furthermore, it provides important initial insights into the range of interactions between bacteria and eukaryotes in these harsh environments."
Harsh environment
Some of the team of authors participated in the 'ANT-XXIII/9' expedition of the German research vessel 'Polarstern' to Antarctica. They took 26 soil samples – at five distances between zero and 80 meters, and at three depths between zero and 30 cm – in front of a slowly retreating glacier in the Larsemann Hills, on the southern shore of Prydz Bay. They used high-throughput DNA barcoding to measure bacterial and eukaryotic biodiversity. The further the distance from the glacier, the more time for ecological succession since the ground was left exposed.
"By distinguishing between intracellular iDNA from living organisms and extracellular eDNA from dead organisms, we could reveal colonizers and locally extinct species preserved in soils. This allowed us to understand the relationships between prokaryotic and eukaryotic microorganisms and gain insights into their interactions over time," said Wagner.
The researchers found a total of 2,829 genetically defined species, of which 40% in the form of eDNA, while overall species richness was 10.3 times greater for bacteria than for eukaryotes. Every distance from the glacier had its own unique range of species. Typically, the diversity of iDNA was greatest in the top layer.
Strength in unity
Closest to the glacier, were so-called 'cryophilic' (cold-loving) fungi. These are thought to be pioneers which contribute to the first phase of soil formation, which then allows other species to settle.
The authors used network analysis to determine which species had the same pattern of local presence versus absence across samples. Consistent coexistence may imply shared niches between species, metabolic dependencies, or novel mutualisms.
"We detected previously unrecognized associations between bacteria and eukaryotes, for example between certain green algae and bacteria, which may promote nutrient exchange. We also found consistent co-occurrence of certain fungi and actinobacteria, which suggests that these fungi could provide carbon for the bacteria by degrading organic matter," said Wagner.
"Our results indicate that microbial survival in extreme Antarctic habitats may be made possible by tightly linked consortia of species that optimize the utilization of resources," concluded Wagner.
These results mean that current estimates for species richness across Antarctica need to be revised upwards. They also suggest potential novel mutualisms between bacteria and eukaryotes that need to be confirmed experimentally, for example through microcosm experiments under defined environmental conditions.
"By focusing on both current and past lineages of microbes, our study shows how colonization and environmental alteration through ecological succession helped change the extreme habitat of Antarctica's Larsemann Hills, making them gradually more hospitable to the current considerable diversity of life," said Wagner.
