IV. Tolerance Adaptations
c. adaptation to temperature
If we purify a given type of protein from species with different body temperatures
and measure the stability of the protein, what we typically find is what's
shown for the muscle protein actin shown on this figure. This work, done
by Dr. Robert Swezey, shows how the stability of actin varies among warm-
and cold-adapted species. Actin from the warm-adapted desert iguana, whose
core temperature might reach 47 degrees Celsius, is much more stable than
actins from cold-adapted Antarctic fishes that die of heat death near 4
degrees Celsius.
When we look at deep-sea fishes, most of which live at temperatures of 1-3
degrees above zero, we would expect that if pressure had no effect on protein
stability--if there were no selection for tougher proteins in the deep sea--then
deep-sea proteins would show relatively low stability, and would be very
similar to those of polar fishes. What we find instead is that for actin,
from three different deep sea fishes, the protein is tougher than even the
protein from a bird or a mammal. So, even though this is a very cold-adapted
group of organisms, this one protein turns out to have a very, tough structure.
We think this is a reflection of the necessity of having a more rigid protein
to be able to withstand the crushing pressures of the deep sea. Some of
these fishes do get down to depths of 3-5 kilometers.
We typically think of tolerance adaptations in the deep sea in terms of pressure
when we're dealing with physical factors. But when we look at the hydrothermal
vents, we find a very interesting situation in terms of an extraordinarily
large and very steep thermal gradient. I want to look at a few data that
concern the way in which different hydrothermal vent species are distributed
within this incredible thermal field, and then look at some of the mechanisms
that might be conferring adaptations not just to high pressure but also
to different temperatures in the vents field. One of my points here is to
illustrate how important temperature is as an environmental variable in
governing where organisms occur. We find that through the vent ecosystem,
there are characteristic differences in habitat temperature that correlate
very well with physiological properties of the organisms. So physiological
adaptations play major roles in the structuring of ecosystems.
I've drawn this cartoon to illustrate the types of water
masses that are present at the hydrothermal vents. As I said before, the
ambient bottom water is very cold. Around the hydrothermal vents near the
East Pacific rise and the Galapagos spreading center most of the water is
cold, relatively rich in oxygen and lacking in hydrogen sulfide. I'll come
back to sulfide in just a moment to talk about the symbiotic systems that
thrive at the vents.
There are two extremes of water: the cold extreme and the warm extreme.
The warm extreme is water that is exiting from the black smoker chimneys.
The black smoker chimneys are putting out what's called "end member"
water. What "end member" refers to is that it is water that has
not been diluted with any of this cold bottom water. The end member water
remains liquid because it's under a pressure of about 250 atmospheres at
the Galapagos and East Pacific rise sites.
The water stays in a liquid state even though it's super heated. The black
smoker water is also depleted in oxygen but it can have very high concentrations
of hydrogen sulfide, concentrations in the millimole range as high as concentrations
that you find in some smelly mud flats. Sulfide, of course, is what gives
the rotten egg smell to mud flats. Biologically, the most interesting waters
at the vents are what are called the warm water vent waters. This is where
there occurs a mixing of the very cold bottom water and this ultra-hot black
smoker water. As you'd expect, there is quite a temperature gradient in
the warm water vents. Temperatures can go from 2 degrees Celsius up to about
20 degrees Celsius with pulses perhaps of 40 degrees Celsius or 50 degrees
Celsius. It's very hard to get an upper limit on this number because of
the very rapidly changing temperature over distance and over time. Oxygen
is variable. Sulfide is variable.
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