Environmental Engineering Reference
In-Depth Information
Reduced metabolism conserves water as well as scarce
food. The ability to live on air-dried food without any ac-
cess to water, the production of concentrated excreta,
hiding in burrows, venturing out mostly at night, and
tolerating salt water are other common thermoregulative
adaptations among desert mammals. Camels have partic-
ularly effective adaptations (Gauthier-Pilters and Dagg
1981). They are able to forage on dry, thorny plants, do
not drink during cooler months even when water is
offered, tolerate long spells without water (up to 10-15
days at 30
C-35
C), can lose as much as 40% of their
body weight, and have an almost instantaneous rehydra-
tion ability as they drink an equivalent of more than 30%
of body weight within 10-20 min.
Cold environments are much more extensive on the
Earth than extremely hot niches. Besides vast polar
deserts there is also the ocean: except for the topmost
1200 m, all of it remains constantly below 5
C, and the
underlying sediments are permanently at about 3
C.
Microorganisms that prefer temperatures lower than
15
C are considered psychrophilic, and many of them
live at close to 0
C (Russell and Hamamoto 1998). Liv-
ing microbes are found in supercooled cloud droplets.
Psenner and Sattler (1998) reported their occurrence at
altitudes above 3000 m in the Alps at around
5
C.
They are also found in brine solutions, which remain liq-
uid at well below the freezing point. The most extreme
psychroecosystem was discovered in the perennial Ant-
arctic lake ice in the McMurdo Dry Valleys (Priscu et al.
1998). Solar heating of the sediment layer containing
sand and microbes blown from the surrounding cold
deserts and embedded in the 3-6-m-thick ice produces
miniature pockets of water that contain bacteria and
cyanobacteria.
In order to survive in the planet's ice-laden polar
waters (
1.4
Cto
2.15
C), Notothenioids (teleost
fish) produce antifreeze proteins (glycopeptides), whose
adsorption to minute ice crystals stops their growth and
lowers the freezing point (Fletcher, Hew, and Davies
2001). Other marine organisms protecting their cells by
secreting ice nucleators into the extracellular fluids are
molluscs, both bivalves and gastropods, living in inter-
tidal zones that are temporarily exposed to low tempera-
tures (Loomis 1995). Littorina littorea, a snail from the
northeastern United States, may survive with more than
70% of its total water content frozen when it is exposed
to temperatures as low as
30
C; barnacles survive even
with 80% of ice in their extracellular tissues. Glycine-rich
antifreeze proteins are also found among many terrestrial
arthropods (beetles, mites, spiders), but these organisms
also survive by insulating their bodies by ice formed
across their cuticles, and by extending the supercooling
capacities of water, from which they remove ice nucle-
ators (Duman 2001). Small volumes of pure water can
be supercooled by as much as 40
C (the point of sponta-
neous nucleation), and antifreeze proteins can lower this
temperature further. Alaskan willow cone gall fly larvae
supercool to
56
C. Among metazoans, turtles and
amphibians also use antifreeze proteins together with
ice-nucleating proteins to initiate the formation of tiny
extracellular ice crystals as they freeze solid while preserv-
ing their vital intracellular structures (Storey and Storey
1988).
Endotherms cope with cold climate by highly effective
insulation. Arctic wolves and caribous have skin temper-
atures comparable to those for a well-clothed human
even at
32
C. Experiments with shorn, shaven, or
hairless animals demonstrate increased heat losses by ra-
