Life on the edge: O2 binding in Atlantic cod red blood cells near their southern distribution limit is not sensitive to temperature or haemoglobin genotype.
Atlantic cod are a commercially important species believed to be threatened by warming seas near their southern, equatorward upper thermal edge of distribution. Limitations to circulatory O2transport, in particular cardiac output, and the geographic distribution of functionally different haemoglobin (Hb) genotypes have separately been suggested to play a role in setting thermal tolerance in this species. The present study assessed the thermal sensitivity of O2binding in Atlantic cod red blood cells with different Hb genotypes near their upper thermal distribution limit and modelled its consequences for the arterio-venous O2saturation difference, Sa-vO2, another major determinant of circulatory O2supply rate. The results showed statistically indistinguishable red blood cell O2binding between the three HbI genotypes in wild-caught Atlantic cod from the Irish Sea (53° N). Red blood cells had an unusually low O2affinity, with reduced or even reversed thermal sensitivity between pH 7.4 and 7.9, and 5.0 and 20.0°C. This was paired with strongly pH-dependent affinity and cooperativity of red blood cell O2binding (Bohr and Root effects). Modelling of Sa-vO2at physiological pH, temperature and O2partial pressures revealed a substantial capacity for increases in Sa-vO2to meet rising tissue O2demands at 5.0 and 12.5°C, but not at 20°C. Furthermore, there was no evidence for an increase of maximal Sa-vO2with temperature. It is suggested that Atlantic cod at such high temperatures may solely depend on increases in cardiac output and blood O2capacity, or thermal acclimatisation of metabolic rate, for matching circulatory O2supply to tissue demand.
Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, The University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK sbarlow168@gmail.com michaelb@liverpool.ac.uk.
Samantha L
SL
Barlow
Centre for Environment, Fisheries and Aquaculture Science (CEFAS), Lowestoft NR33 0HT, UK.
Julian
J
Metcalfe
Centre for Environment, Fisheries and Aquaculture Science (CEFAS), Lowestoft NR33 0HT, UK.
David A
DA
Righton
Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, The University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK sbarlow168@gmail.com michaelb@liverpool.ac.uk.
Michael
http://orcid.org/0000-0002-0793-1313
M
Berenbrink
D000064:Acclimatization; D000818:Animals; D004912:Erythrocytes / Q000378:metabolism*; D048389:Gadus morhua / Q000097:blood* / Q000235:genetics / Q000502:physiology*; D005838:Genotype; D057232:Global Warming; D006454:Hemoglobins / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D011485:Protein Binding; D013696:Temperature
D006454:Hemoglobins; D010100:Oxygen
Bohr effect; Climate change; Gadus morhua; O2 affinity; Oxygen transport; Thermal tolerance