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Seasonal acclimatisation of muscle metabolic enzymes in a reptile (Alligator mississippiensis)

Frank Seebacher^1,*, Helga Guderley², Ruth M. Elsey³ and Phillip L. Trosclair, III³

¹ School of Biological Sciences A08, University of Sydney, New South Wales 2006, Australia
² Départment de Biologie, Université Laval, Québec, PQ G1K 7P4, Canada
³ Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, 5476 Grand Chenier Highway, Grand Chenier, LA 70643, USA

View larger version (15K): [in a new window]   Fig. 1. Mean daily body temperatures of alligators were significantly lower in winter compared with in summer. In winter, body temperatures increased with body mass, but there were no mass-related differences between alligators in summer. Redrawn from F. Seebacher et al., in press.

View larger version (16K): [in a new window]   Fig. 2. Daily amplitudes of body temperatures (Tb). Alligators experienced significantly greater fluctuations in daily Tb in winter compared with in summer. Redrawn from F. Seebacher et al., in press.

View larger version (13K): [in a new window]   Fig. 3. Metabolic enzyme activities of alligators in winter and summer at different assay temperatures. There were significant differences between seasons and assay temperatures in all enzymes: (A) lactate dehydrogenase (LDH), (B) citrate synthase (CS) and (C) cytochrome c oxidase (CCO). Note that the activity of LDH and CCO does not differ between winter animals at 15°C and summer animals at 30°C and that CS activity is significantly elevated at 15°C in winter compared with in summer.

View larger version (14K): [in a new window]   Fig. 4. Q10 values for each enzyme in winter and in summer. The thermal sensitivity of mitochondrial enzymes – citrate synthase (CS) and cytochrome c oxidase (CCO) – decreased significantly in winter, but Q10 values for lactate dehydrogenase (LDH) increased in winter compared with in summer.

View larger version (12K): [in a new window]   Fig. 5. Ratio of enzyme activity of males to females. The activity of mitochondrial enzymes [citrate synthase (CS) and cytochrome c oxidase (CCO)] was significantly greater in males compared with in females, but there was no difference between sexes in the activity of lactate dehydrogenase. There was no interaction between sex and assay temperature or season, and pooled data for each enzyme are shown.

View larger version (13K): [in a new window]   Fig. 6. Enzyme activities (means ± S.E.M.) plotted against body mass. Activities did not change with body mass for any enzyme, at any season or at any assay temperature. Examples shown here are from winter (solid circles) and summer (open circles) at 15°C. Solid lines indicate mean activities in winter; broken lines indicate mean activities in summer.