Among the perciform sub-order Notothenioidei, a variety of adaptations to cold temperatures exist (Coscia et al. 2011; di Prisco et al. 2007), with the most dramatic of these exemplified in the highly specialised crown group Channichthyidae (icefishes) (Tota et al 1997; Cheng et al. 2009). Consider the icefish Chionodraco hamatus, endemic to the frigid waters of the Antarctic in the Southern Ocean (Garofalo et al 2009). This species can survive in temperatures approaching -2.5 °C (Bilyk and DeVries 2010) and hence, is well suited to meet the demands of cold temperature survival. The major adaptation of C. hamatus for survival in cold temperatures is the expression of antifreeze glycoproteins (AFGPs) (Bilyk and DeVries 2010) which are absent in most teleosts but necessary for survival in frigid waters (DeVries 1988). Further adaptations of the icefish clade relate to the distinguishing synapomorphy of the group (di Prisco et al. 2007; Verde et al. 2004; Tota et al. 1997), the uniform absence of haemoglobin (Ruud 1954 in Holeton 1970). These adaptations, involving modified circulatory, respiratory, and integumentary systems, enable sufficient oxygenation of the tissues in the absence of haemoglobin (Eastman 1993, in Kock 2005). I will focus on two major functions of these adaptations: increased oxygen transport and increased oxygen uptake. This report will discuss how AFGPs, in addition to the myriad adaptations for increased oxygen transport and uptake, enable C. hamatus to successfully endure the frigid waters of the Antarctic
a) Antifreeze glycoproteins increase freeze tolerance in icefish blood and body fluids
To survive in the frigid waters of the Antarctic, C. hamatus utilizes an evolutionary key innovation shared by all members of the Antarctic clade of nototheniods, antifreeze glycoproteins (di Prisco et al. 2007; Eastman 2000; DeVries 1971). Composed of only alanine, threonine, N-acetylgalactosamine and galactose (DeVries 1971), AFGPs are thought to provide an “antifreeze” effect in the blood and tissue fluids of icefish (Fletcher et al. 2001) through preventing water molecules from attaching to the surface of ice crystals with which the AFGPs adsorb onto (DeVries 1971). Thus, through the use of its circulatory system to move AFGPs throughout its blood and other tissue fluids, C. hamatus is able to prevent the formation of ice within its body. Survival in frigid waters for related teleosts without the key innovation of antifreeze proteins is impossible ( DeVries 1988).
To determine the effect of AFGPs on the freezing point of icefish blood serum, researchers have utilized and improved upon the method DeVries (1971) modified from Ramsay and Brown (1955). DeVries’ (1971) technique involved freezing very small samples of blood serum and isolated aqueous AFGPs from icefish, with slow subsequent warming until a single small but stable ice crystal remained in each sample. Next the solutions were either slowly warmed or chilled, and the...