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208 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA 471.6 mM for control crabs and 503.8 mM for acclimated crabs. This reflects a change in ionic regulation with Na+ being hyper-regulated after repressurization compared to the sea water salinity. The cause and the role of this change are unclear. High calcium and potassium levels were correlated with normoxia but no clear physiological interpretation can be made. In most crustaceans, hypoxia, high temperature or stress usually induce a lactate and/or urate response (Bridges, 2001). For hydrothermal vent crustaceans, a strong lactate response was observed in Bythograea thermydron under severe hypoxia (31.1 mM lactate in 5 % O 2 ) and up to 20.4 mM lactate was measured in Cyanagraea praedator after a 4h30 stabulation at atmospheric pressure. Thus the absence of lactate response in S. mesatlantica is original. An absence of lactate response was also observed in the buried isopod Saduria entomon which has only about 3 mM lactate after 144 h exposure to severe hypoxia (Hagerman et Szaniawska, 1988). Response in term of phenotypic plasticity / Hc structure Phenotypic plasticity has been observed in several species during development (Cancer magister) (Terwilliger et Terwilliger, 1982, Terwilliger et Dumler, 2001) or in response to environmental changes (Callinectes sapidus, Panulirus elephas, Panulirus mauritanicus) (Bellelli et al., 1988, Condó et al., 1991, Mangum, 1994). In our study, no effect of acclimation condition was found on the subunit composition for S. mesatlantica. Thus phenotypic plasticity at the subunit level is not involved in the physiological response to respiratory stresses under the conditions tested here. The short term adaptation in our crabs must be rather hemolymphatic than phenotypic. It can be interpreted in term of metabolic cost : the cost of protein synthesis for short time adaptation (16 h) must be higher than a hemolymphatic response such as urate production or a local acidification near metabolizing tissues coupled with a strong Bohr effect. A strong response in complex proportions was observed, with a higher proportion of hexamer in high temperature acclimated crab and a higher proportion of dodecamer in low temperature acclimated crabs. A similar difference in complex proportions under temperature adaptation was observed for Astacus leptodactylus and was associated with a higher affinity of the hexamer (Decker et Foll, 2000). In our case, functional properties of purified complexes from a single individual could not be investigated due to the low quantity of available material for each crab. The potential physiological advantages for oxygen transport of this proportion adjustment are unclear. Previous studies have shown similar properties for both complexes (Ocypode quadrata (Johnson, 1987)), a higher affinity for the hexamer (Astacus leptodactylus, Callinectes sapidus (Mangum et al., 1991), Carcinus aestuarii (Dainese et al., 1998)) or the dodecamer (Penaeus monodon (Beltramini et al., 2005), Litopenaeus vannamei (y. Pan et al., 2008), Calappa granulata at high pH (Olianas et al., 2006)) depending on
5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 209 the species. Different thermal stability is not involved since it was shown that no dissociation occurs upon incubation at 35°C (Chausson, 2001). In S. mesatlantica we observed a correlation between high dodecamer proportion and high protein content : this enables to decrease blood viscosity and osmotic pressure at the very high protein contents observed in some crabs (up to 200 µg/µl and 282 µg/µl), compared to what it would be with the same protein quantity under the hexameric form. It must also be noted that freezing can cause partial dissociation of dodecamers, as observed for several decapod species Morris (1988). The correlation between sodium and protein concentration and the dodecamer proportion can possibly reflect stabilizing effect of one complex or the other during freezing. The ideal control experiment would be to perform SEC experiments on board on freshly sampled hemolymph. An interesting alternative explanation is that hydrostatic pressure could have an effect on oligomerization. Elevated hydrostatic pressure can modify chemical equilibria and rate constants depending on the specific volumes and activation volumes of reactions and has an effect on ionic interactions, hydrogen bonds and hydrophobic cores. Pressure can stabilize or destabilize protein conformation depending on the type of interaction involved in the tertiary structure. Dissociation of oligomeric proteins is usually promoted by high pressures (Gross et Jaenicke, 1994, Boonyaratanakornkit et al., 2002). Glossoscolex paulistus giant hemoglobin is dissociated at pressures above 1 kbar (equivalent to 10 000 m depth) (Silva et al., 1989). Lactate dehydrogenase apoenzyme is progressively dissociated/inactivated at pressures comprised between 0 and 80 MPa (0 and 800 bar, equivalent to 8 000 m depth) (Gross et Jaenicke, 1994). To our knowledge, all deep-sea crabs studied to date have higher hexamer proportions than shallow-water crabs (including for a bathyal species non-endemic from hydrothermal vents, Chaceon affinis (Chausson, 2001)). These proportions could reflect a specific molecular adaptation of the oligomeric complexes to deep-sea pressure. Functional properties S. mesatlantica Hc had a very high affinity for O 2 and exhibited a strong Bohr effect. Along with no or inverse temperature effect on affinity, this is a common feature of hydrothermal-vent crustacean Hc and is adaptive in hypoxic environments for efficient loading at the gills and unloading near the metabolizing tissues (Hourdez et Lallier, 2007). The strong lactate effect observed and the absence of urate effect for S. mesatlantica is not typical of hydrothermal species. Cyanagraea praedator Hc is insensitive to lactate (Chausson, 2001) whereas lactate sensitivity is small for Bythograea thermydron Hc ( ∆log(P 50) ∆log[lactate] =-0.06 (Sanders et Childress, 1992)), moderate for Rimicaris exoculata Hc (-0.12 (Lallier et Truchot, 1997)) and Chorocaris chacei (-0.16 (Lallier et al., 1998)). From our data, L-lactate is not a physiological modulator of Hc for S. mesatlantica given the occurrence of a strong lactate effect, a high basal lactate level and no lactate
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THESE DE DOCTORAT DE L’UNIVERSITE
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i Résumé / Abstract Réponse adap
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iv SOMMAIRE 4.2 Objectifs de l’é
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2 CHAPITRE 1. INTRODUCTION Les éco
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FIG. 1.5 - Localisation des princip
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134 CHAPITRE 4. PLASTICITÉ PHÉNOT
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Page 243 and 244: Bibliographie Adair, G. S. The hemo
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Page 247 and 248: BIBLIOGRAPHIE 241 Farmer, C. S., J.
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Page 253 and 254: BIBLIOGRAPHIE 247 Rainer, J., C. P.
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Page 259 and 260: Liste des figures 1.1 Cycle des mar
Page 261: LISTE DES FIGURES 255 4.17 Profils
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Table des matières Résumé Sommai
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TABLE DES MATIÈRES 261 4.3.5 Spect
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TABLE DES MATIÈRES 263 Table des m
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