Abstract
The Arctic and Antarctic marine faunas differ by age and isolation. Fishes of the two polar regions have undergone different regional histories that have driven the physiological diversities. Antarctic fish are highly stenothermal, in keeping with stable water temperatures, whereas Arctic fish, being exposed to seasonal temperature variations, exhibit higher physiological plasticity. This study reports the characterization of the oxygen transport system of three Arctic species of the family Gadidae, namely the Arctic cod Arctogadus glacialis, the polar cod Boreogadus saida, and the Atlantic cod Gadus morhua. Unlike Antarctic notothenioids, the blood displays high multiplicity, i.e. it has three hemoglobins, similar to many other acanthomorph teleosts. In the most abundant hemoglobin, oxygen binding is modulated by heterotropic effectors, with marked Bohr and Root effects. Remarkably, in two species (A. glacialis and B. saida), the Hill coefficient is very close to one in the whole pH range, indicating the apparent absence of cooperativity. The amino acid sequences have been used to gain insight into the evolution history of globins of polar fish. The results indicate that Arctic and Antarctic globins have different phylogenies and lead us to suggest that the selective pressure of environment stability allows the phylogenetic signal to be maintained in the Antarctic sequences, whereas environmental variability would tend to disrupt this signal in the Gadidae sequences.
Highlights
The main differences between the Arctic and the Antarctic are the older age and longer isolation of the latter [1]
This study reports the characterization of the oxygen transport system of three Arctic species of the family Gadidae, namely the Arctic cod Arctogadus glacialis, the polar cod Boreogadus saida, and the Atlantic cod Gadus morhua
The results indicate that Arctic and Antarctic globins have different phylogenies and lead us to suggest that the selective pressure of environment stability allows the phylogenetic signal to be maintained in the Antarctic sequences, whereas environmental variability would tend to disrupt this signal in the Gadidae sequences
Summary
The main differences between the Arctic and the Antarctic are the older age and longer isolation of the latter [1]. The first glaciation, including shelf-ice formation, had occurred 36 million years ago (mya) in the early Oligocene. About 25 mya, the formation of the Polar Front, which followed the opening of the Drake passage, further isolated the Antarctic marine fauna from the world ocean. The Antarctic and Arctic fish faunas differ in age, endemism (denoting species native to a given geographical area), and taxonomic diversity. The Arctic fauna has no endemic higher taxonomic category equivalent to Antarctic Notothenioidei, and there has been no comparable adaptive radiation of any fish group. The North Atlantic and North Pacific character of the marine fauna reflects the continuity of shelf areas between the Arctic and boreal regions [2]. Some of the marine components are representative of groups, including the cosmopolitan fauna of the late Cretaceous period. Oxygen carriers provide interesting systems for studying the relationship between environmental conditions and molecular evolution, because the capacity of fish to colonize a large variety of habitats appears strictly correlated to the molecular and functional differences encountered in their Hb systems [6]
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