XV. Questions from the audience
Q: My question is how are new hydrothermal vents populated?
A:That's always the first question that's asked. The colonization of the
vents is an absolutely intriguing thing. The first problem is the needle
in the haystack problem. How does a vent organism that's releasing gametes
or larvae into the water have any hope that the little guys are going to
find another vent site. A trivial amount of the sea floor has the right
waters. It's been speculated with absolutely no evidence that maybe some
of the larval forms of the vent animals can sniff sulfide and follow sulfide
trails if they have the ability to swim. That's really an unknown. What
we do know is that the colonization is very effective. About five years
ago, just by good luck, one of the ships was going over a site in the East
Pacific rise seismic when activity occurred. They took Alvin down and they
found a brand new vent site. In fact, they found what was called worm "barbecue"
site, an underwater eruption which had killed off a whole community of tube
worms. They revisited that site. They did a time lapse study where the time
lapses were about six or eight or nine months apart. That's the point about
Riftia being the fastest growing invertebrate arose. Within about
a year to a year and a half, the sites had full sized tube worms. So it's
clear that larvae find these sites and settle effectively - and they just
grow like gang busters when there is the right mixture of sulfide and oxygen.
Childress has been very successful in developing technology for holding
a lot of the vent animals, especially the big tube worms. When he feeds
them the right amount of sulfide the worms grow centimeters a month.
Q: I always thought that the pressure-volume laws only worked for gases.
In terms of the athleticism argument in being related to darkness, there
are fish down there, I believe, that use photophores as searchlights. Therefore,
would it be worthwhile to check those fish in the sense of their athleticism
compared to other fish that can't do that?
A: That's a very good point. One of the problems in doing work with
deep sea organisms, at least as it applies in most studies, is that you
work with what you can catch. I think Bruce has shown this very well in
some of the presentations I've heard him give. As we get better ways of
viewing things unobtrusively, meaning that we don't scare away the things
that move fast, we do find in the midwater that there are a lot of things
that move really fast. There has been a certain amount of what you call
capture artifact in the past. String a net through the water and you're
basically catching things that don't get out of the way. There could be
very fast things down there one would never see by dragging a net through
the water at maybe 6 or 8 knots. So there are undoubtedly fishes down there
that move very fast. In the slide on enzyme "athleticism" versus
depth, there was quite a lot of scatter in any single depth. So it's clear
that fishes with different feeding strategies differ. It would be nice if
we could find fishes that go around with sniper scopes, it would be interesting
to see what they're doing.
Now, concerning your first question about pressure volume relationships,
it's hard to intuit how something which is in an aqueous phase is going
to face the sorts of things that Boyle's law would suggest about pressure/volume.
It turns out when people have done molecular simulations of the changes
in water organization that occur near proteins during function, a lot of
the change in volume that occurs is not so much the change in how efficiently
the protein is packed, but it's changes in the organization of water around
the molecule. I suppose the easiest way to intuit it is to realize that
water reaches its maximum density around four degrees. So water can change
its density a lot depending on physical conditions or depending on its chemical
environment. For example, if the protein thrusts out a charged group into
water, that will shrink the volume of the system because the water will
organize around the charged group. So when a protein is changing conformation,
it's going to be reversibly exposing to water, groups from the protein that
will effect water structure. That's where most of the volume changes will
start to come from. They're substantial. They can be 50-100 cubic centimeters
per mole of protein. By mechanisms that we don't understand, deep sea organisms
have learned to minimize these volume changes.
Q: How do the animals that are there get from place to place? Those which
colonize, where do they come from originally? Are they archaic types that
simply evolve there? Are they more modern types that somehow migrate?
A:In terms of the vent organisms? I have minimal expertise to answer
that, but let me touch on one point. Life may have originated at the vents.
That's a hypothesis, but there is more and more evidence that it's a feasible
idea. When you look at the ancestral forms by building molecular phylogenies,
we find hyperthermophilic organisms appear to be ancestral. The thought
is that the hydrothermal vents were a very high energy environment. They've
been around for a long time. You've got a lot of energy there in reduced
compounds like hydrogen sulfide. You don't have ultraviolet radiation coming
at you. So the vents may have been where life originated. The modern taxa
that we find most prevalent at the vents actually appear to be quite ancient
residents of these areas. In fact, they have found some barnacles at the
vents that people thought were extinct. It's like finding a Coelacanth off
of Madagascar.
|
|
|
Narrative Index
BioForum Index
