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First published online August 17, 2007
Journal of Experimental Biology 210, 2999-3014 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006007

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Temperature adaptation in two bivalve species from different thermal habitats: energetics and remodelling of membrane lipids

Fabrice Pernet^1,*, Réjean Tremblay², Luc Comeau³ and Helga Guderley⁴

¹ Institut de Recherche sur les Zones Côtières, 232B rue de l'Église, Shippagan, Nouveau-Brunswick, E8S 1J2, Canada
² Institut des Sciences de la Mer, 310 allée des Ursulines, Rimouski, Québec, G5L 3A1, Canada
³ Department of Fisheries and Oceans, Science Branch, Gulf Fisheries Centre, PO Box 5030, Moncton, New Brunswick, E1C 9B6, Canada
⁴ Département de Biologie, Université Laval, Québec, Québec, G1K 7P4, Canada

View larger version (11K): [in this window] [in a new window]   Fig. 1. (A) Experimental protocol for low temperature and spring–summer simulation experiment with mussel Mytilus edulis and oyster Crassostrea virginica. Circles indicate dates of clearance rate measurements and lipid sampling. Routine O2 was measured on 12 April, 4 May and 31 May and O2min was measured on 8 June after starving the animals used for routine O2. (B) Schematic of the split-split plot experimental design. T°C=9, 4 or 0. See Materials and methods for further details.

View larger version (18K): [in this window] [in a new window]   Fig. 2. (A) Clearance rate (CR) and (B) oxygen consumption rate of mussels and oysters for a standard animal 1 g in whole body dry mass (mean ± s.e.m, N=2 tanks). CR was affected by the combination of temperature, species and date whereas oxygen consumption was affected only by the combination of species and date. Routine O2 was measured on 12 April, 4 May and 31 May, and O2min was measured on 8 June after starving the animals used for routine O2.

View larger version (29K): [in this window] [in a new window]   Fig. 3. Characteristics of the neutral lipids in mussel and oyster digestive glands as a function of time. Data presented here are (A) the concentration of triglycerides, (B) the unsaturation index and (C–F) the mol % of polyunsaturated fatty acids (PUFA; C), 22:6n-3 (D), 20:5n-3 (E) and 18:4n-3 (F). Values are means ± s.e.m, N=2–6 tanks. The green line indicates dietary values. The unsaturation index is calculated as the sum of the molar percentage of each unsaturated fatty acid multiplied by the number of double bonds within that fatty acid. Data from different overwintering temperatures were pooled as this effect was not significant. Different letters indicate significant differences.

View larger version (81K): [in this window] [in a new window]   Fig. 4. Relative mobilisation of fatty acids from the digestive glands of mussels and oysters overwintered at 0, 4 and 9°C during the overwintering period (A), the spring–summer simulation (B) and the overall period of study (C). The relative mobilisation of individual fatty acids was calculated as the ratio of initial to final levels in the TAG for each time interval. Values are means ± s.e.m, N=2. A ratio greater than, equal to, or lower than unity shows that the fatty acid is released more, equally, or less readily, respectively, than the total TAG-fatty acids. Values for fatty acids >2 mol % of the total are arranged in increasing order of relative mobilisation from bottom to top.

View larger version (45K): [in this window] [in a new window]   Fig. 5. Characteristics of the membrane lipids in mussel (M) and oyster (O) digestive glands (DG) and gills, as a function of time (left) and species and tissues (right). (A) The phospholipid to sterol ratio, (B) the unsaturation index and (C–E) the mol % of polyunsaturated fatty acids (PUFA; C), 22:6n-3 (D) and 20:5n-3 (E) in the polar lipids. Values are means ± s.e.m, N=2–6 tanks. The unsaturation index is calculated as the sum of the molar percentage of each unsaturated fatty acid multiplied by the number of double bonds within that fatty acid. Data from different overwintering temperatures were pooled as this effect was not significant. Different letters indicate significant differences.

View larger version (21K): [in this window] [in a new window]   Fig. 6. (A) Regression models using temperature as the explanatory variable and the unsaturation index of animals acclimated at 0°C, 4°C, 9°C (April 12) and 20°C (June 8) as the response variable in digestive glands (DG) and gills of mussels and oysters. (B) Mol % of polyunsaturated fatty acids (PUFA), 22:6n-3, and 20:5n-3 in the gills of mussels and oysters acclimated at 0°C, 4°C, 9°C (April 12) and 20°C (June 8) as a function of temperature.

View larger version (10K): [in this window] [in a new window]   Fig. 7. Mol % of arachidonic acid (20:4n-6) in the polar lipids as a function of temperaturexspeciesxdate. Values are means ± s.e.m, N=2 tanks). Data from different overwintering groups and tissues were pooled as these effects were not significant. Different letters indicate significant differences.

View larger version (9K): [in this window] [in a new window]   Fig. 8. Mol % of non-methylene interrupted dienoic fatty acids (22:2 NMI) in the polar lipids as a function of speciesxdate (A; data from different tissues pooled) and tissuexdate (B; data from different species pooled). Values are measn ± s.e.m, N=2–6 tanks. Data from different overwintering temperatures were pooled as this effect was not significant. Different letters indicate significant differences.