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
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 -8°C, which means that the cold night-time
temperatures are a genuine threat to their survival.
 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?
 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
South African Agency for Science and Technology Advancement for more on research
and careers in Antarctica
Related articles:
Big bang in Antarctica - crater found under ice.
Scientific
evidence for the impact of climate change in Antarctica.
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