Mechanisms and evolution of hypoxia tolerance in fish

Abstract

The ability of an organism to acquire O2from its environment is key to survival and can play an important role in dictating a species' ecological distribution. This study is the first, to our knowledge, to show a tight, phylogenetically independent correlation between hypoxia tolerance, traits involved in dictating O2extraction capacity and the distribution of a group of closely related fish species, sculpins from the family Cottidae, along the nearshore marine environment. Sculpins with higher hypoxia tolerance, measured as low critical O2tensions (Pcrit), inhabit the O2variable intertidal zones, while species with lower hypoxia tolerance inhabit the more O2stable subtidal zone or freshwater. Hypoxia tolerance is phylogenetically independently associated with an enhanced O2extraction capacity, with three principal components accounting for 75 per cent of the variation inPcrit: routine O2consumption rate; mass-specific gill surface area; and whole blood haemoglobin (Hb)–O2-binding affinity (P50). Variation in whole blood Hb–O2P50is strongly correlated with the intrinsic O2-binding properties of the purified Hb while the differences in the concentration of the allosteric Hb modulators, ATP and GTP, provide a Hb system with substantial plasticity for survival in a highly O2variable environment.