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November 2003

Feature

 


Icy resilience the key to survival in Antarctica's 
land animals

Dr Brent Sinclair

On a continent where it is dark for six months of the year and daylight for the entire summer, you might expect the long summer days to blend into one, but on a trip last summer to Cape Hallett, Antarctica, as part of a joint New Zealand-South African team of scientists, Dr Brent Sinclair and team discovered the opposite. Antarctica is home to some feisty, resilient and really tiny creatures.

The field camp at Cape Hallett after a light snowfall. The pyramid tents were our 'bedrooms', while the long sausage-shaped tents provided lab space. The hill in the background was home to the main population of the springtail Isotoma klovstadi.The spectacular Cape Hallett is near the northern tip of the Ross Sea, the big bite out of the continent below New Zealand, and home to about 60 000 pairs of Adelie penguins, and a terrestrial ecosystem unique in Antarctica for its diversity. An Antarctic terrestrial ecosystem is not a particularly spectacular affair. It has been kept simple by brutal winters, millions of years of isolation and unstoppable glaciers, resulting in an ecosystem composed of the survivors: mosses, algae and bright orange lichens are the forests and fynbos at Cape Hallett, while animals measured in fractions of millimetres make up the fauna. The king of the beasts is a two millimetre predatory mite with the awe-inspiring (?) name of Coccorhagidia gressitti, and there are about eight other species of mites, and three species of springtails, the millimetre-long primitive insects they had travelled to Cape Hallett to study.

At up to 2mm in length, Isotoma klovstadi is the giant of Cape Hallett, and is often seen foraging in huge numbers on algae and moss (above). These springtails are very active, run quickly (even at sub-zero temperatures), and have quite a jump on them. Isotoma klovstadi is mostly found on scree slopes, and is quite abundant even at higher altitudes.

Springtails, members of the order Collembola have a history as long as the presence of insects on land, and fossils show that their basic wingless, eyeless body plan has not changed substantially in that time. In fact, they are so old that experts disagree about whether they are insects at all, and one recent paper has even suggested that they may be more closely related to shrimps.

Springtails are cosmopolitan, with species found all round the world, but they really come into their own in the Arctic and Antarctic, where their small size and tolerance of cold often allow them to dominate (at least in terms of numbers) among the land animals. A bit of bare earth, some simple plants for food and an occasional trickle of liquid water is all they ask.

A team of three scientists from Stellenbosch University'and New Zealand's University of Otago, spent three months at Cape Hallett unravelling the ways in which springtails survive the harsh environment they live in, and learning a thing or two about themselves, no doubt.

Springtails die if they freeze, and survive the cold by a strategy called freeze avoidance. Essentially, they rely on their small size, in combination with protein, sugar and sugar-alcohol antifreezes to keep their body fluids liquid at well below freezing point - lower than -35 C in some individuals during the spring!

However, during the summer, the springtails have a short window of opportunity in which they can feed, grow and breed. Unfortunately, when they have full guts, ice nucleators in the algae they eat can greatly increase their freezing point to around -5 to -8C, which means that the cold night-time temperatures are a genuine threat to their survival.

Team member Dr Jaco Klok works at a microscope in the laboratory tent.Air temperatures varied through the day. Cape Hallett is flanked to the south by the Hallett Peninsula, which is over 1000m high. Since the sun circles overhead (and is lowest and in the South at 'night'), the team's camp and study site were in the shade during the 'night'. With clear skies and no direct sun, the temperature dropped rapidly, leading to a pronounced cycle of high(ish) temperatures during the day, and freezing temperatures at night. While the team huddled in their tents during the harshest weather - how did the insects cope with the sharp decrease in temperature at night?

Isotoma klovstadi grazes in huge groups on algae at Cape Hallett.  However, algae in the gut can provide a nucleus for ice formation, potentially causing them to freeze and die when night time temperatures drop below zero.One of the species of springtail provided the answer. At up to 2mm in length, Isotoma klovstadi is the giant of Cape Hallett, and is often seen foraging in huge numbers on algae and moss. These springtails are very active, run quickly (even at sub-zero temperatures), and have quite a jump on them. Isotoma klovstadi is mostly found on scree slopes, and is quite abundant even at higher altitudes. Almost by accident, the team found that this species can combat this danger by an astonishing flexibility in their physiology: between midday and midnight, springtails decrease the average temperature they can survive by more than 10 C. This allows them to have the best of both worlds: eating during the day, and surviving the cold during the night. How the springtails manage this astonishing flexibility is a question scientists have not yet been able to answer, but ongoing work on the proteins and sugars that they produce in response to cold will hopefully provide us with some answers.

These large daily cycles in temperature are not just a feature of Antarctica. In Southern Africa, big daily cycles in temperature are quite common in the high altitude areas of the Karoo and Highveld, not to mention the unpredictable winter (and sometimes summer!) snowfalls that often drop in to the Drakensberg and the mountains of the Western Cape. Add another variable of climate change to this equation and you may begin to wonder just how animals cope with sharp changes in temperature.

The study at Cape Hallett, says Sinclair, had a much bigger goal in mind - to provide some valuable information into how climate change will affect the distributions and physiology of other animals. The Antarctic, according to Sinclair, is the ideal place to conduct these studies as the very simple ecosystem is easier to understand than the complex ecosystems in Africa and elsewhere. Sinclair maintains that an understanding of how the springtails, for example, adapt to fluctuations in temperature may tell us a thing or two about managing ecosystems that will be susceptible to climate change in Southern Africa.

Already, the case of the daily changes in cold tolerance of the springtails provides serious food for thought: if their simple model ecosystem is so flexible on a daily basis, then how much do we not know about the ecosystems we see around us every day? And how much do we not know about what they do every night? No doubt, the team will be out seeking these answers, and hopefully, next time, on drier land.


More information:

Brent Sinclair is a New Zealand Science and Technology Postdoctoral Fellow in the Spatial, Physiological and Conservation Ecology Group in the Zoology Department at the University of Stellenbosch. Email bjs@sun.ac.za
For more information on the Cape Hallett trip, visit www.sun.ac.za/zoology/sinclair/capehallett.htm

This Research was supported by the New Zealand Foundation for Research, Science and Technology; Antarctica New Zealand; the South African National Antarctic Programme and the University of Stellenbosch. The work on daily changes in springtail physiology was published this month in the Journal of Insect Physiology.

For more information on the Spatial, Physiological and Conservation Group at the University of Stellenbosch, visit www.sun.ac.za/zoology/space or contact Professor Steven Chown Email slchown@sun.ac.za

 

 

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