A simple bioassay is described for insulin-like activity (lLA) which is based on the incorporation of (3H)glucose into the lipids of isolated rat fat cells. Total lipids were extracted by adding toluene-based scintillation fluid direcdy to the incubation tlasks, and the radioactivity in the lipids measured by liquid scintillation counting. Insulin dose-response curves with (2-3H)-, (3-3H) and (6-3H)glucose were compared and those obtained with (2-3H)glucose and (3-3H) glucose were found suitable for routine use.

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Phenotypic plasticity is a mechanism by which organisms can alter their morphology, life history or behaviour in response to environmental change. Here, we investigate shell plasticity in the intertidal gastropod Littorina littorea in response to the ocean acidification and elevated temperature values predicted for 2100, focusing on shell traits known to relate to protection from predators (size, shape and thickness) and resistance to desiccation (aperture shape). We also measured and desiccation rates (measured as percentage water loss). Ocean acidification was simulated by bubbling carbon dioxide into closed-circuit tanks at concentrations of 380 and 1000 ppm, giving respective pH levels of 8.0 and 7.7; temperatures were set at 15 or 20°C. Both low pH and elevated temperature disrupted the overall investment in shell material; snails in acidified seawater and elevated temperature in isolation or in combination had lower shell growth rates than control individuals. The percentage increase in shell length was also lower for individuals kept under combined acidified seawater and elevated temperature, and the percentage of shell thickness increase at the growing edge was lower under acidified and combined conditions. Shells were also more globular (i.e. had lower aspect ratios) under elevated temperature and lower pH. Desiccation rates were lower at low pH and high temperature. Counter to predictions, water loss did not relate to shell biometric measures but was negatively correlated with adenosine triphosphate (ATP) concentrations. Finally, ATP concentration was positively correlated with shell thickening and weight, confirming the idea that negative effects of exposure to elevated p CO 2 /low pH and elevated temperature on shell morphology may occur (at least in part) through metabolic disruption.

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In the future, marine organisms will face the challenge of coping with multiple environmental changes associated with increased levels of atmospheric Pco(2), such as ocean warming and acidification. To predict how organisms may or may not meet these challenges, an in-depth understanding of the physiological and biochemical mechanisms underpinning organismal responses to climate change is needed. Here, we investigate the effects of elevated Pco(2) and temperature on the whole-organism and cellular physiology of the periwinkle Littorina littorea. Metabolic rates (measured as respiration rates), adenylate energy nucleotide concentrations and indexes, and end-product metabolite concentrations were measured. Compared with values for control conditions, snails decreased their respiration rate by 31% in response to elevated Pco(2) and by 15% in response to a combination of increased Pco(2) and temperature. Decreased respiration rates were associated with metabolic reduction and an increase in end-product metabolites in acidified treatments, indicating an increased reliance on anaerobic metabolism. There was also an interactive effect of elevated Pco(2) and temperature on total adenylate nucleotides, which was apparently compensated for by the maintenance of adenylate energy charge via AMP deaminase activity. Our findings suggest that marine intertidal organisms are likely to exhibit complex physiological responses to future environmental drivers, with likely negative effects on growth, population dynamics, and, ultimately, ecosystem processes.