Ancient invertebrates adapting to life between glacial ice crystals

The Southern Alps are anything but frozen wastelands. West Coast glaciers teem with microscopic animals, including plump, snub-nosed tardigrades whose lineage stretches back more than 500 million years. Four newly identified species offer a rare glimpse into life at high altitude, but what will happen as their icy homes retreat? NZASE speaks with University of Otago evolutionary biologist and geneticist Professor Peter Dearden, co-author of two papers on the tardigrade discovery, about how isolation shapes species in extreme environments.

Introduction

When chunks of ice from three Southern Alps glaciers began thawing in his laboratory in 2020, Professor Peter Dearden expected to find little living in them. The samples had been collected from the west-facing slopes of Whataroa, Fox and Franz Josef glaciers following a hunch from a visiting scientist; similar glaciers in North America are home to highly adapted annelid ice worms. Realising little was known about life in these high-altitude glacial habitats, which are also accumulation zones for windblown organisms swept up from the rainforest below, Peter decided: “…it’d be really great to go and see if there’s anything up there.”

What emerged from the samples surprised him. Chipped from solid surface ice above the glacier equilibrium line—the boundary where annual snowfall and melting balance—the samples revealed more than 5,000 microscopic animals: tardigrades, rotifers, nematodes, flatworms and tiny crustaceans, including one the team dubbed the ‘New Zealand ice shrimp’.

“There’s actually a whole community of organisms living right at the top of our glaciers that is unprecedented. The fact that these organisms can live there quite happily in environments that we would find unsurvivable in bad weather, I think that’s a remarkable thing. I think they have much to teach us about how to cope with extreme environments.”

Tardigrades

Among the samples collected were tardigrades. Despite bumbling around on eight stubby legs, rarely growing larger than a millimetre, these invertebrates are incredible masters of endurance. There are about 1,500 species worldwide—and around 90 in New Zealand—inhabiting various habitats from mountaintops and tropical rainforests to deep-sea trenches, even our backyards. Around 25,000–18,000 years ago, when a near-continuous ice cap covered much of the Southern Alps, Peter suspects that only one or two tardigrade species occupied the range. As the climate naturally warmed and the ice fragmented, populations may have become isolated on separate glaciers, allowing them to diverge genetically and eventually form distinct but similar-looking species.

This meant that although Peter could sequence DNA from the tardigrade samples at the University of Otago, the species collected were so physically similar that he needed a tardigrade expert to microscopically examine them to biologically characterise them. Slide-mounted specimens were sent to Polish tardigrade expert Dr Krzysztof Zawierucha and his colleagues, who compared features and DNA. Four species in two previously unknown genera—Kopakaius, from kōpaka, te reo Māori for glacier, and Kararehius, from kararehe, meaning animal—were identified.

Adaptations

Adaptations occur when inherited variations help some individuals survive and reproduce more successfully than others. Over many generations, those variations may become more common within a population. Environmental conditions—including temperature, available food, predators and disease—help determine which traits are advantageous.

Some features of the glacier tardigrades may be adaptations, although there’s not enough evidence to be certain. Three newly discovered Kopakaius species are darkly coloured, unlike most tardigrades, which are transparent. Their pigment might provide protection from ultraviolet radiation, Peter says, but transparent tardigrades and other unpigmented animals survive on the same glaciers.

“Tardigrades have this reputation of being able to survive all kinds of radiation, whether they’re darkly coloured or not. It’s interesting to speculate that it has something to do with UV exposure, but I don’t think it’s very clear…[so] that’s new and exciting.”

Kopakaius also has unusually short, stumpy claws resembling those of Cryobiotus, a distantly related glacier tardigrade found overseas. This is an example of parallel evolution: distinct evolutionary lineages independently developing similar features in response to similar environmental pressures. Peter suspects the claws may help the animals leverage themselves between tightly packed ice grains.

“There’s some specialised function of this shape of claw that both of these species have independently evolved because it works well,” says Peter. “These sorts of core structures somehow make a tardigrade’s life easier when they’re living in a pile of ice.”

When unrelated species repeatedly evolve similar solutions, it suggests that the environment is exerting strong evolutionary pressure. Only a limited range of inherited variations may work well under those conditions, making similar outcomes more likely.

While some species evolve relatively quickly, others stay the same for long periods. Evolutionary stasis happens when the environment doesn’t change much or when a body design works so well that major changes aren’t needed. The newly discovered Kararehius genus, although genetically distinct, looks similar to Adropion—which usually lives in moist mosses, lichens, soil and leaf litter. One possibility, Peter suggests, is that the tardigrade body—already capable of surviving freezing, thawing and drying—is versatile enough to function across many habitats without undergoing major visible change.

Left: The inhabitants from samples collected from the glaciers. Credit: https://doi.org/10.1038/s41598-021-83256-3

Cryptobiosis

Many terrestrial and freshwater tardigrades have an extraordinary survival adaptation. When their surroundings dry out—and, in some species, when they freeze—they contract into a barrel-shaped form called a tun and enter cryptobiosis. Their metabolism drops to extremely low or undetectable levels. Some tardigrades have been revived after spending more than 30 years frozen at –20°C. In laboratory experiments, particular species in cryptobiosis have also survived brief exposure to temperatures close to absolute zero or around 150°C, intense radiation and enormous pressure. When water and suitable conditions return, they rehydrate, resume activity and wander off to feed and reproduce. This evolutionary adaptation lets them survive in extreme environments that would kill most life.

*ABOVE: Glacier sites for collections on April 28, 2020. https://doi.org/10.1016/j.ympev.2022.107634*

Adaptation for the future

Predicting what lies ahead for high-altitude tardigrades is difficult, Peter says, because scientists do not yet know how widely they are distributed. Researchers found them on glaciers, but that may reflect where they chose to look. “Does that mean that they’re only in glaciers or are they actually living through snow throughout the Southern Alps?” Intriguingly, just across the Southern Alps at a similar altitude on the Tasman Glacier, researchers haven’t found similar ecosystems.

Because so little is known about how tardigrades live, interact and feed on the ice, more funding is required. “We need to take the microscopes up there and see what the hell they’re doing,” says Peter. “Spend some time with them. Unfortunately, I haven’t found anyone who’s willing to give me cash to go and find out.”

And as glaciers shrink, these animals are losing their icy homes. Tardigrade lineages have endured natural warming since the last ice age, but human-driven climate change is happening much faster, leaving populations less time to move or adapt. Even so, Peter remains cautiously hopeful. “These are species that are incredibly robust. There’s hope these groups, tardigrades in particular, I suspect they’re going to find a way to continue living.”

Professor Peter Dearden

Peter’s career in biology began with being told not to study it. Despite a fascination with natural history—he’d spent childhood summers tramping through Nelson Lakes and Mount Aspiring national parks—his high school deemed him too smart for biology and steered him towards the ‘real sciences’ of physics and chemistry. Luckily, university changed everything. Inspired by genetics teacher Geoff Rickards, Peter studied genetics, biochemistry and physiology at Victoria University of Wellington, graduating with a BSc (Honours) before completing a PhD in nervous system development at Imperial College London.

Born in Canada and brought to New Zealand at two, Peter grew up with science on one side of the family and the humanities on the other. His mother is a microbiologist and botanist; his father, a professor of classics. “I think it means I’ve had a weird education. But that sort of classical thought and philosophy, and the ways that historians and archaeologists approach things, are absolutely things that I think about. I’m almost trying to link the biology we do to a broader context in the history of science and knowledge.”

Peter went on to hold research roles at Cambridge, in Canada and at the University of Otago, with his work spanning developmental biology and zoology, crop protection and inherited eye disease. He became a University of Otago professor in 2016. Along the way, Peter has helped build New Zealand’s scientific capability well beyond the university. As founding director of Genomics Aotearoa, he strengthened genomics research nationwide, while his mobile ‘Lab-in-a-Box’ brought hands-on molecular biology into schools and communities throughout New Zealand and the Pacific. He also provides genomics and breeding advice to DOC’s Kākāpō Recovery Programme.

Peter received the Ross Crozier Medal for genetics and the Callaghan Medal for science communication in 2014, followed by the MJD. White Medal for genetics in 2026. That same year, he became a Ngā Ahurei Fellow of Royal Society Te Apārangi.

Peter lives in Dunedin with his wife, three children and a dog–bear called Barkerly.

Activity

While some tardigrades tough it out in remote, icy extremes, others share our everyday world, lumbering their way through gardens, creeks and forests. With a low-powered or digital microscope and a clump of moss soaked in water, students can glimpse these ancient survivors up close. And while discovering new species is thrilling, the researchers believe many more undiscovered tardigrades are still out there—the next new tardigrade species waiting to be named, could be in our backyards.

Ngā kupu

Hukapapa: ice
Kā Roimata o Hine Hukatere (The tears of Hine Hukatere): Franz Josef Glacier
Te Moeka o Tūawe (the bed of Tuawe): Fox Glacier
Kā Tiritiri o te Moana: Southern Alps
Waiparahoaka: glacier
Whakarewa: melt

New Zealand Science Curriculum | Phase 3 | Biological Science | Organism Diversity | Year 7: Survival Adaptations
Individuals who survive in their environment pass on their traits to offspring.

Ancient invertebrates adapting to life between glacial ice crystals | Professor Peter Dearden