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Life Aboard Ship, Dispatches From South of the "Roaring Forties"
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July 5, 2004
We are now in
transit to Tristan da Cunha from Bouvetoya, (see Cruise Track, http://www.icefish.neu.edu/index.php)
and everyone is mostly bored because
we’re not doing any trawling or collecting. We are sleeping, eating,
doing laundry, watching movies, playing cards or foosball, catching
up on reading (recreational or scientific), writing research papers or proposals,
editing photographs, bird and whale-watching, and generally counting
the days until we get there. Believe it or not, this is the toughest part of
the cruise. The earlier parts that involved hard work were always varied and
interesting.
With no scientific work underway, the PALMER's scientists kick back with a little Foosball in the helo hangar. Two Italians, a German and a Kiwi go mano a mano.
Why are we going to Tristan? After all, it is an island that is neither cold nor subantarctic. In fact, it could be considered almost subtropical. We hope so, because we are looking forward to being able to lie in the sun for a change!
Tristan da Cunha has the northernmost occurrence of a notothenioid fish. Its
name is Bovichtus diacanthus (common name, Klipfish), and it lives in the tide
pools and shallow subtidal waters to a depth of about 20m (65 ft.) around the
island. It is an endemic species, that is, it is found only at Tristan and
nowhere else in the world. It is of great importance and interest to us because
the geneticists and physiologists aboard need to study its response to living
in such a warm environment.
The Klipfish, found only in shallow waters off Tristan da Cunha, is the PALMER's quarry at its next landfall. The critter's scientific name is Bovichtus elongatus, a close relative of B. diacanthus. (illustration from Fishes
of the Southern Ocean, O. Gon and P. Heemstra, editors)
I'll try to explain. The suborder Notothenioidei includes a number of closely
related families that share similar characters (as you would expect). Two
of these are a physiological tolerance (even a requirement) for low temperatures,
and the production of antifreeze that keeps tissues and fluids from freezing
at the extreme temperatures at which most species live. The Bovichtidae are
the most generalized family in the suborder, and thus are considered to represent
most closely the ancestors of the whole group. Note that they are NOT the
ancestors, but are probably most similar to them!
Bovichtids include eleven species, of which only one is Antarctic; the rest are more northern, and nowhere do two species live together in the same area. Most have distributions restricted to isolated islands and nowhere else (just like B. diacanthus at Tristan). That species appears to have the highest temperature tolerance of any in the suborder (up to 27° C, almost 81° F). The question is, what does this mean in relation to its physiology, and how does it differ genetically from its colder-living relatives?
Different research groups on board will look at the biochemistry, physiology, and anatomy of B. diacanthus to try to determine first, what was the notothenioid ancestor like, and second, what changes were necessary to enable it to live at sub-zero temperatures? More specifically: Does it have antifreeze? Does it have the gene for antifreeze but fail to express it? The upper lethal temperature for many Antarctic notothenioids is +6°C; what physiological mechanisms does this species have that enable it to so far exceed that temperature? For instance, does it have a wider variety of isozymes (same enzyme but different temperature tolerance) to cope with higher temperatures?
In very cold waters, oxygen is at a relatively high concentration and some fishes have lost hemoglobin entirely because they do not need it (see http://www.boatus.com/cruising/icefish/work.asp). Myoglobin is a similar oxygen-carrying molecule that occurs only within muscles and acts to distribute oxygen within the tissues (as opposed to hemoglobin, which acts to distribute it throughout the blood). Many notothenioids that still have hemoglobin have lost myoglobin in the heart for the same reason: there is enough oxygen so that special mechanisms are not needed. Does B. diacanthus have myoglobin? If so, what other differences, if any, does it have relative to the colder-living species, which have focused their enzyme systems to the narrow colder temperature range at which they live; some of them are never exposed to temperatures above freezing. If it does not have other enzymes, how does it survive in a warm, relatively oxygen-poor, environment?
So, we hope that this one species, which is supposed to be common and of which we will try to collect 20-30 living specimens, will provide keys to answering some fundamental questions about the evolution of the icefishes. In the next Bulletin I hope to be able to tell you about what happened at Tristan and what it was like.
Just as an aside, we have seen NO evidence of humanity (other than ourselves and the NBP) since we left South Georgia on June 10. No ships, no jetsam, no buildings, no contrails from aircraft, nada. In the modern world in which many people take care to NEVER be out of contact with others, this is not only unusual, but an odd feeling.
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