Biologists have described two new tardigrade genera and associated species — two of which are new to science — from the mountain glaciers of New Zealand’s Southern Alps.
First discovered in 1773, tardigrades (phylum Tardigrada) are a diverse group of microscopic invertebrates with eight legs and body size ranging from 50-1,200 µm (micrometers).
Also known as water bears or moss piglets, these creatures can live for up to 60 years and are well-known for their ability to survive extreme conditions.
They are able to survive for up to 30 years without food or water, for a few minutes at temperatures as low as minus 272 degrees Celsius (minus 457 degrees Fahrenheit) or as high as 150 degrees Celsius (302 degrees Fahrenheit), and minus 20 degrees Celsius (minus 4 degrees Fahrenheit) for decades.
They withstand pressures from virtually 0 atm in space up to 1,200 atm at the bottom of the Marianas Trench, and are also resistant to radiation levels up to 5,000-6,200 Gy.
Tardigrades inhabit various limno-terrestrial (soil, bryophythes, lichens, algae mats) and aquatic (sediments, plants) environments, from polar to tropical regions and from high mountains peaks to deep oceans.
Due to their tolerance to unfavorable environmental conditions, microscopic size and long-range dispersal capabilities, they are cosmopolitan and inhabit remote and often hostile environments.
Although tardigrades are well studied worldwide, their diversity and ecology in cold environments remain poorly recognized despite their important roles in trophic webs and ecosystem function.
The richness of tardigrade species in extreme glacial habitats is relatively low compared to that of surrounding ecosystems, likely due to strong selection pressures including permanently low temperatures, high irradiation, and periodic freezing.
Importantly, glacier tardigrades are mostly distinct from their limno-terrestrial counterparts, as evidenced by DNA and/or phenotypic dissimilarity.
“We describe two new genera of tardigrades from the accumulation zones of three New Zealand glaciers by an integrative taxonomic approach combining morphological, morphometric and genetic data,” said lead author Dr. Krzysztof Zawierucha, a researcher in the Department of Animal Taxonomy and Ecology at Adam Mickiewicz University and the Faculty of Forestry and Wood Sciences at the Czech University of Life Sciences Prague, and his colleagues from Poland, New Zealand and the United States.
“The first genus, named Kopakaius, displays extraordinary and unique morphology that has not been reported in tardigrade literature thus far, whereas the second, Kararehius, is erected from the cosmopolitan, polyphyletic genus Adropion.”
The first genus is represented by three genetically distinct species, one of which, Kopakaius nicolae, is new to science.
The second includes a new species named Kararehius gregorii and three former members of the genus Adropion: Kararehius behanae, Kararehius tricuspidatum, and Kararehius triodon.
Like other high mountain glacier tardigrades, Kopakaius tardigrades have dark pigmentation, while Kararehius lack pigmentation, comparable to glacial Arctic and Antarctic species.
Kopakaius nicolae inhabits Whataroa Glacier only while the remaining two Kopakaius species occur on Fox and Franz Joseph Glaciers, suggesting low dispersal capabilities. Kararehius gregorii inhabits Fox and Franz Joseph Glaciers.
“Cold environments are not just a repository of ancient invertebrates preserved in a frozen realm, but rather represent highly active ecosystems for viable and diverse forms of micrometazoans, including tardigrades,” the authors said.
“Tardigrades have been found on snow in forests, snow fields in open mountain areas, as well as on ice surfaces above the equilibrium line altitude.”
“These findings identify a new path for studies on psychrophilic metazoans that will be important to describe and understand diversity, adaptation, dispersal, and evolutionary links between ‘cold-loving’ and ‘cold-resistant’ invertebrates.”
“Our study contributes to this knowledge by revealing (a) two new genera of tardigrades from glacier ice, (b) their deep phylogenetic structure in mitochondrial DNA, (c) convergent evolution of morphological characters, and (d) ice fragmentation that likely triggered speciation during the Pleistocene.”
The results were published this week in the journal Molecular Phylogenetics and Evolution.
Krzysztof Zawierucha et al. Two New Tardigrade Genera from New Zealand’s Southern Alp Glaciers Display Morphological Stasis and Parallel Evolution. Molecular Phylogenetics and Evolution, published online October 5, 2022; doi: 10.1016/j.ympev.2022.107634
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