Maximum cardiac performance of Antarctic fishes that lack haemoglobin and myoglobin: exploring the effect of warming on nature’s natural knockouts

• Published in: Conservation Physiology
• Main Authors: Egginton, Stuart, Axelsson, Michael, Crockett, Elizabeth L, O’Brien, Kristin M, Farrell, Anthony P
• Other Authors: Todgham, Anne, NSERC Canada, Swedish Research Council, University of Leeds, Natural Sciences and Engineering Council of Canada, National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2019
• Subjects: Management, Monitoring, Policy and Law; Nature and Landscape Conservation; Ecological Modeling; Physiology; Antarc*; Antarctic; Icefish
• Online Access: http://dx.doi.org/10.1093/conphys/coz049; http://academic.oup.com/conphys/article-pdf/7/1/coz049/30133082/coz049.pdf

Abstract Antarctic notothenioids, some of which lack myoglobin (Mb) and/or haemoglobin (Hb), are considered extremely stenothermal, which raises conservation concerns since Polar regions are warming at unprecedented rates. Without reliable estimates of maximum cardiac output ($\dot{Q}$), it is impossible to assess their physiological scope in response to warming seas. Therefore, we compared cardiac performance of two icefish species, Chionodraco rastrospinosus (Hb−Mb+) and Chaenocephalus aceratus (Hb−Mb−), with a related notothenioid, Notothenia coriiceps (Hb+Mb+) using an in situ perfused heart preparation. The maximum $\dot{Q}$, heart rate (fH), maximum cardiac work (WC) and relative ventricular mass of N. coriiceps at 1°C were comparable to temperate-water teleosts, and acute warming to 4°C increased fH and WC, as expected. In contrast, icefish hearts accommodated a higher maximum stroke volume (VS) and maximum $\dot{Q}$ at 1°C, but their unusually large hearts had a lower fH and maximum afterload tolerance than N. coriiceps at 1°C. Furthermore, maximum VS, maximum $\dot{Q}$ and fH were all significantly higher for the Hb−Mb+ condition compared with the Hb−Mb− condition, a potential selective advantage when coping with environmental warming. Like N. coriiceps, both icefish species increased fH at 4°C. Acutely warming C. aceratus increased maximum $\dot{Q}$, while C. rastrospinosus (like N. coriiceps) held at 4°C for 1 week maintained maximum $\dot{Q}$ when tested at 4°C. These experiments involving short-term warming should be followed up with long-term acclimation studies, since the maximum cardiac performance of these three Antarctic species studied seem to be tolerant of temperatures in excess of predictions associated with global warming.