Strange Life in an Improbable Place - Scientific American Ice fishes, in particular, provide remarkable insight into the power of an extreme environment to shape life. As the Southern Ocean cooled from temperate conditions to its chronically frigid state—the freezing point of seawater near Antarctica is –1.87 degrees Celsius—during the past 40 million years, most major fish groups there became locally extinct. Today the fish fauna around Antarctica is dominated by species (approximately 100) of a single suborder, the Notothenioidei. Having been isolated in a freezing ocean for so long, these fishes (as well as marine invertebrates) can now live only at cold temperatures; in fact, most die if temperatures rise as little as five degrees C. As Eastman and DeVries describe, two astounding adaptations enabled these fishes to exploit this underutilized habitat: (1) they evolved potent antifreeze molecules that prevent their body fluids from freezing (a constant hazard in icy waters), and (2) some species of this swimbladderless group evolved neutral or near-neutral buoyancy (weightlessness in water), which allowed them to feed throughout the food-rich water column, in contrast to their denser, bottom-living relatives. The ice fish family (which includes 16 different species) provides us with further surprises. During a visit to South Georgia in 1929, a young Norwegian marine biologist, Johan T. Ruud, thought he was being made the butt of a joke when he was told by whalers that some of the local fishes had no blood (fish known as blodlaus-fisk). Sure enough, no red blood emerged from them, which was puzzling because red blood cells and hemoglobin are thought to be constants in vertebrate life. Ruud was not able to return to South Georgia until 1953 to investigate this mystery, which he describes in “The Ice Fish” from the November 1965 issue. One of Ruud’s important conclusions was that evolutionary loss of red cells and hemoglobin could occur only in very cold and oxygen-rich waters—precisely the conditions of the Southern Ocean.
Posted on: Tue, 09 Dec 2014 04:38:13 +0000
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