Thermal tolerance and hypoxia tolerance are associated in blacktip reef shark (Carcharhinus melanopterus) neonates

Bouyoucos, Ian A., Morrison, Phillip R., Weideli, Ornella C., Jacquesson, Eva, Planes, Serge, Simpfendorfer, Colin A., Brauner, Colin J., and Rummer, Jodie L. (2020) Thermal tolerance and hypoxia tolerance are associated in blacktip reef shark (Carcharhinus melanopterus) neonates. Journal of Experimental Biology, 223 (14). jeb221937.

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Thermal dependence of growth and metabolism can influence thermal preference and tolerance in marine ectotherms, including threatened and data-deficient species. Here, we quantified the thermal dependence of physiological performance in neonates of a tropical shark species (blacktip reef shark, Carcharhinus melanopterus) from shallow, nearshore habitats. We measured minimum and maximum oxygen uptake rates (ṀO2), calculated aerobic scope, excess post-exercise oxygen consumption and recovery from exercise, and measured critical thermal maxima (CTmax), thermal safety margins, hypoxia tolerance, specific growth rates, body condition and food conversion efficiencies at two ecologically relevant acclimation temperatures (28 and 31°C). Owing to high post-exercise mortality, a third acclimation temperature (33°C) was not investigated further. Acclimation temperature did not affect ṀO2 or growth, but CTmax and hypoxia tolerance were greatest at 31°C and positively associated. We also quantified in vitro temperature (25, 30 and 35°C) and pH effects on haemoglobin–oxygen (Hb–O2) affinity of wild-caught, non-acclimated sharks. As expected, Hb–O2 affinity decreased with increasing temperatures, but pH effects observed at 30°C were absent at 25 and 35°C. Finally, we logged body temperatures of free-ranging sharks and determined that C. melanopterus neonates avoided 31°C in situ. We conclude that C. melanopterus neonates demonstrate minimal thermal dependence of whole-organism physiological performance across a seasonal temperature range and may use behaviour to avoid unfavourable environmental temperatures. The association between thermal tolerance and hypoxia tolerance suggests a common mechanism warranting further investigation. Future research should explore the consequences of ocean warming, especially in nearshore, tropical species.

Item ID: 65083
Item Type: Article (Research - C1)
ISSN: 1477-9145
Keywords: Aerobic scope, Critical thermal maximum, Growth, Haemoglobin–oxygen affinity, Temperature dependence, Thermal preference
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Copyright Information: © 2020. Published by The Company of Biologists Ltd
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A version of this publication was included as Chapter 5 of the following PhD thesis: Bouyoucos, Ian Alexander (2020) Ecological energetics of climate change for tropical sharks. PhD thesis, James Cook University, which is available Open Access in ResearchOnline@JCU. Please see the Related URLs for access.

Funders: Australian Research Council (ARC), L'Oréal-UNESCO Women in Science Foundation, ARC Centre of Excellence for Coral Reef Studies (CECRS), Natural Sciences and Engineering Research Council (NSERC), Laboratoire d'Excellence CORAIL, Station d'Ecologie Espérimentale of the Centre de Recherches Insulaires et Observatoire de l'Environnement (CRIOBE), French Ministère de l'Environnement, Company of Biologists (COB), Passions of Paradise Student Research Award, Oceania Chondrichthyan Society (OCS), British Ecological Society, Europcar Polynesie, Higher Degree Research Scheme, James Cook University (JCU)
Projects and Grants: ARC PDE150101266, L'Oréal-United Nations Educational, Scientific and Cultural Organization (UNESCO) Women in Science Foundation Fellowship (2015–16), NSERC Discovery Grant, COB (JEBTF-170510), JCU Postgraduate Research Scholarship
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Date Deposited: 01 Dec 2020 00:28
FoR Codes: 31 BIOLOGICAL SCIENCES > 3109 Zoology > 310912 Comparative physiology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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