Individual variation in heat tolerance and metabolism in marine Antarctic organisms

Climate change is one of the main concerns to Antarctic biodiversity. Since temperature plays a crucial role in various biological traits, it is key to understand how warming may affect organisms specialized to live in the cold habitats. Although heat tolerance of several polar species is known, little emphasis has been given to individual variation and its relationship with other biological traits such as metabolic performance. In this study, we investigated the association between thermal sensitivity in metabolism (Q₁₀) and heat tolerance (z) in six Antarctic marine organisms, including two fish species (Harpagifer antarcticus and Notothenia coriiceps), three crustaceans (Bovallia gigantea, Glyptonotus antarcticus, and Paraceradocus miersi), and one mollusk (Trophon nucelliformis). For this, we measured routine metabolic rates (RMR, mg O₂/h) followed by heat tolerance measurements to reconstruct dose-response curves employing sublethal assays or thermal-collapse time (TCT) curves. Analyses reveal a negative relationship between the intercept and the slope of the temperature tolerance curves (CT_max and z values, respectively) against Q₁₀, but only when T. nucelliformis was included in the generalized linear model. Therefore Q₁₀ may be a good predictor of heat tolerance, but it is not true for chordate or arthropod species studied. Additionally, CT_max and z values exhibited a positive relationship consistent with previous studies. This study represents the first example of temperature tolerance curves quantified on an individual basis, and the analyses provide some evidence that thermal sensitivity in metabolism and heat tolerance are correlated. In future studies, it will be crucial to determine whether this relationship is robust and how it may impact the response of different lineages to accelerated warming.