Physiological and evolutionary aspects of myoglobin expression in the haemoglobinless Antarctic icefishes

Summary

Fish fauna of the Southern Ocean present an unique combination of biological characteristics and evolutionary history compared with those from other marine systems. Two features figure prominently in setting these organisms apart from fishes of temperate zone and even polar boreal seas.

First, the level of endemism of Antarctic fishes is unparalleled in other ocean systems. Of the 250+ species of fish known to inhabit the Southern Ocean, the dominant group, in terms of both species numbers (>100) and abundance (50–90% of captures) are members of the perciform suborder Notothenioidei (Dewitt, 1971; Anderson, 1990; Eastman, 1993). With few exceptions, fishes of the six notothenioid families are indigenous to waters surrounding Antarctica where they have evolved during the last 25–40 My in isolation under conditions that are both thermally stable and severely cold. Within this monophyletic group are species displaying a wide diversity of ecologies and life histories, from sluggish demersal to active pelagic habits.

The second major feature that sets Antarctic notothenioid species apart from the ichthyofauna of other marine systems is their long geographical isolation in waters that are the most severely cold, thermally stable aquatic habitat on the planet. The best estimates are that thermal isolation of Antarctica began with the development of circumpolar currents in the late Oligocene and was followed shortly thereafter with the establishment of the Antarctic Convergence (about 20 million years ago) (Kennett, 1977, 1980). The demise of most non-notothenioid fishes and radiative expansion of this suborder in coastal Antarctica apparently began with the significant ocean cooling that predated these events (Anderson, 1990).