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By Peter Rejcek
Scientists who normally spend much of the austral summer
in the McMurdo Dry Valleys conducting long-term studies
on that polar desert ecosystem are taking their research
on the road.
Byron Adams , an associate professor of biology at Brigham
Young University , will lead a small team of colleagues
on a series of short excursions to the Beardmore Glacier
in the Transantarctic Mountains this year. The project
is something of a reconnaissance mission to determine
if viable communities of microorganisms inhabit the exposed
soils in a high and dry area dominated by ice.
“We’re really interested about the biodiversity
of these organisms that are there, and we’re particularly
interested in their evolutionary history as well,”
explained Adams, a member of the McMurdo Dry Valleys Long
Term Ecological Research (LTER) program, a multidisciplinary
study of the lakes and soils in Antarctica’s largest
ice-free region.
The soil-dwelling organisms of the McMurdo Dry Valleys
— such as the tardigrade and wormy nematodes —
are found throughout the world. However, many of the Antarctic
species are endemic, implying a long, unbroken evolutionary
history.
That’s the story that Adams can read in the molecular
structures of the animals, particularly nematodes, when
compared to their distant cousins on other southern hemisphere
continents.
Ice block
There’s just one problem, Adams said. The models
used by glaciologists to represent the extent of the Antarctic
ice sheet in the past covers all the areas where these
animals inhabit. That means all the different tardigrades,
nematodes and other metazoans that Adams and his colleagues
in the McMurdo Dry Valleys LTER study only colonized the
region within the last 20,000 years after the ice last
reached its maximum extent.
“That model leaves no room for any refugia for any
of these animals to persist, therefore these areas must
have been completely devoid of organisms that later re-colonized
these areas,” said Adams. But the geographic distribution
and diversity of today’s tiny critters indicate an
evolutionary history on a much greater time scale.
“Biology is telling us a different story than the
models the glaciologists have come up with,” Adams
said. “We’re arguing that these organisms survived
the Pleistocene glaciation somewhere in Antarctica.”
Adams believes that in high-altitude areas the microorganisms
found refuge from the repeated thrust and retreat of the
ice sheet that marked the 2.5 million years of the Pleistocene,
which ended about 12,000 years ago with the onset of the
relatively warm and stable Holocene. In un-glaciated places
like Mount Seuss, an elevated area in the Dry Valleys,
scientists have found high genetic diversity among the
animals, he added.
“The populations that persisted there seeded these
other areas that opened up” after the ice sheet retreated,
he explained. “[The] most compelling evidence is
that in 15,000 years, 12,000 years, even 20,000 years,
you just can’t produce the diversity of species we
have on continental Antarctica. You just can’t do
that in that short period of time.”
New territory
Adams hopes to add more evidence to support that theory
if his team can find similar diversity in the exposed
soils in the Beardmore region. “We would predict
that these organisms in these isolated populations would
respond in concert to the climate changes, the environmental
changes that are imposed on them. Using tools of molecular
evolution, we can do these types of comparisons,”
he said.
While there have been few biological studies in the mountains,
Adams said researchers do know life exists in isolated
pockets far from the Dry Valleys. In fact, he was the
lead author of a paper published a couple of years ago
in Polar Biology that described the discovery of the southernmost
nematode, Scottnema lindsayae, which New Zealand colleague
Ian Hogg brought back from the mouth of the Beardmore
Glacier. Hogg is also a member of the team headed to the
Beardmore region this year.
“We’ll probably be some of the first biologists
to collect in some of these areas,” Adams noted.
“It’s like going to Mars or the moon for us.
It’s a place where biologists really haven’t
been.”
Documenting distribution
Diana Wall , a soil biologist from Colorado State University
and co-principal investigator on the project, said it
is important for the team to document the distribution
of species outside the Dry Valleys to gauge their resilience
to climate change.
“One of the things we need to know with climate
change is how big the climate envelope is for a particular
species,” explained Wall, entering her 20th season
working in the Dry Valleys. “To know that kind of
thing, we need to know the range of the different species.”
For example, in collaboration with the New Zealand science
program, scientists ventured as far north at Cape Hallet,
about 400 kilometers from the northern edge of the Dry
Valleys. An algae-feeding nematode at the more northerly
location differed from one found in the Dry Valleys, Wall
said.
Climate change
Most climate change studies in Antarctica focus on the
western ice sheet. If anything, the long-term trend in
the McMurdo Dry Valleys, right on the edge of East Antarctica,
has been slight cooling. However, a series of short-term
flooding events in recent years has illustrated how quickly
the system can respond to even minor changes.
“If you turn that temperature gauge half a degree
above freezing for a period of time, you generate a lot
of water,” noted Berry Lyons , who is also on the
McMurdo LTER and is a geochemist from the Byrd Polar Research
Center at The Ohio State University .
“I think these are extremely sensitive systems,
and slight increases in temperature in summer time really
have a profound effect on how much water you generate,”
added Lyons, who is also a co-principal investigator on
the Beardmore team. His role will be to support the biological
study by analyzing the geochemistry of the soils.
“The chemistry is just an aid to better understand
the habitat — the soil’s age and composition,
how much nitrogen and carbon and how much salt,”
he explained. “I think they’re probably going
to look like a lot of the higher elevation soils we see
in the Dry Valleys.”
Going high and dry
That’s different from the floor of the Valleys, where
moisture from streams, lakes and permafrost melt helps
drive the activity, productivity and density of the organisms
in the soil. Wall’s “worm herders” science
team has found nematodes in up to 70 percent of the Dry
Valley soils.
In extremely dry soil areas, she said, only the nematode
Scottnema lindsayae has the temerity to survive, remaining
in an anhydrobiotic state, a sort of stasis where all
metabolic activities cease and it loses up to 99 percent
of its water content until moisture is available. It can
remain that way indefinitely.
“It’s the Rambo [of nematodes]. It’s a
tough worm,” Wall noted.
Added Adams, “We can find old soils that are dry
and have these nematodes in them. We can add water to
them and they come alive. We still don’t know the
answer to the question about how old these things are
and how long they can live in this state.”
Some of those answers may be found where no one has looked
— yet.
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