XI. Athleticism
So one of the approaches that we've used is to try and develop indexes of athleticism.
In other words, can we bring up freshly dead organisms, measure some biochemical
characteristic, and come to some conclusion about their locomotory activity?
The logic here is that the amount of ATP generating capacity that a gram
of muscle contains is a quantitative measure of the muscle's ability to
power locomotory activity. Muscles that work very fast, high power muscles,
have a high level of enzymatic activity for generating ATP. That's very
well established. So our logic is that if we could measure the quantities
of ATP generating activity in a gram of muscle and compare grams of muscle
from a wide range of species, this might be a test of whether or not there
is, in fact, a large reduction in locomotory power with depth through the
water column. So the method is simple.
Here is what we find. In fact there is substantially decreased athleticism in
deep-sea fishes. Here on the Y axis, I've plotted enzyme power per gram
of muscle. The enzyme in question is lactate dehydrogenase of the glycolytic
pathway. That's the pathway that a fish depends on when it's undergoing
bursts of activity during predator-prey interactions. Let me define the
symbols here. The open squares, the highest activities, are from warm bodied
fishes, tuna fishes. These open symbols are for hydrothermal vent fishes.
All the filled symbols are for pelagic fishes collected at different depths.
The species' depth of occurrence is the minimal depth at which it occurs.
We can see among shallow organisms that there is a wide range of enzymatic
power in a gram of muscle. In other words, there is a great range of athleticism
among shallow-living species. Warm-bodied fishes have an enormously high
metabolic rate. All of these enzymatic activities have been measured at
a common temperature, at 10° C. If we were to ramp up the rates in warm-bodied
fishes to 25 or 30 degrees, these rates would be perhaps 3000-4000 times
higher than the rates that we find in a gram of muscle in some of the very
watery deep-sea fishes. The most sluggish deep-sea fishes have only 5-10
units of activity compared to 1000 units in a rapidly swimming tuna fish.
So there has been a tremendous reduction in locomotory activity with depth.
What can we conclude from these patterns of enzymatic activity versus depth?
Because there is a very strong correlation between oxygen consumption rate
and the amount of enzyme power in the swimming muscle, the reductions that
we find in oxygen consumption rate with depth are almost certainly due mostly
to reduction in swimming power.
One of the things that I haven't mentioned yet is the fact that muscle may be
unique in this pattern of depth-related enzymatic activity. See the parallel
dashed lines. They represent an envelope of values that we determined for
enzymatic activity in brain tissue. There is no change in ATP generating
power with depth. This is further evidence that there has been a specific
reduction in the swimming power of these fishes as opposed to their mental
power.
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