Haemoglobin function in aquatic animals: molecular adaptations to environmental challenge

The adaptive nature of haemoglobin function in a diverse range of aquatic e ctothermic vertebrates is demonstrated by its intrinsic oxygen-binding prop erties and by erythrocyte cofactor modulation of Hb function. The selective advantage of heterogeneous isohaemoglobins and polymorphic expression of f unctionally distinct components is considered in relation to environmental oxygen tensions and temperature. The difficulty of comparing physiological adaptations in divergent species is emphasized. Recent population studies s uggest that relatively minor differences in environmental conditions, parti cularly temperature, direct the expression of functionally heterogeneous ha emoglobins, although the thresholds for expression have not been establishe d. Regulatory mechanisms underpinning the molecular mechanisms for hypoxic induction of Hb in aquatic vertebrates are not well understood.