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First published online November 10, 2003

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Metabolic and cardiovascular adjustments of juvenile green turtles to seasonal changes in temperature and photoperiod

Amanda L. Southwood^*, Charles A. Darveau and David R. Jones

Department of Zoology, The University of British Columbia, 6270 University Blvd, Vancouver, BC, Canada V6T 1Z4

View larger version (11K): [in a new window]   Fig. 1. Effects of a laboratory simulation of summer and winter conditions on (A) oxygen consumption (O2), (B) breathing frequency (fB), and (C) percent time spent active of captive juvenile green turtles. Filled bars represent simulated summer conditions (TW=26°C, photoperiod 14 h:10 h light:dark) and open bars represent simulated winter conditions (TW=17°C, photoperiod 10.25 h:13.75 h light:dark). Variables were measured during exposure to summer conditions before and after the winter simulation (26-pre and 26-post, respectively) and after 8 weeks and 16 weeks exposure to winter conditions (17-8w and 17-16w, respectively). There was no statistically significant difference in O2 (P=0.059), fB (P=0.288) or percent time spent active (P=0.400) between treatment groups. N=5 for all treatment groups except 26-post, in which N=4.

View larger version (17K): [in a new window]   Fig. 2. There was a significant positive relationship between activity and oxygen consumption (O2 ; r2=0.63, P<0.001) for juvenile green turtles. Data points for individual turtles are shown for the summer simulation (filled symbols) and winter simulation (open symbols).

View larger version (12K): [in a new window]   Fig. 3. (A) There was a significant correlation between breathing frequency (fB) and oxygen consumption (O2) of green turtles during exposure to summer conditions (fB=-0.496+14.660xO2 -0.83, r=0.982, P=0.018, N=4). Data points represent means ± S.E.M. for individual turtles during exposure to summer conditions before (26-pre) and after (26-post) the winter simulation. (B) The correlation between fB and O2 was much weaker and not significant during exposure to winter conditions (r=0.514, P=0.375, N=5). Data points represent means ± S.E.M. for individual turtles after 8 weeks (17-8w) and 16 weeks (17-16w) exposure to winter conditions.

View larger version (11K): [in a new window]   Fig. 4. Activity (i.u. g-1 wet mass) of (A) citrate synthase (CS), (B) lactate dehydrogenase (LDH) and (C) pyruvate kinase (PK) in flexor tibialis muscle of captive juvenile green turtles (N=5) exposed to summer conditions (filled circles) and after 4 weeks exposure to winter conditions (open circles). CS activity was significantly lower in tissue collected from turtles exposed to winter conditions compared with summer conditions (P<0.001). Conversely, LDH and PK activity were significantly higher during exposure to winter conditions compared with summer conditions (P<0.001), a pattern typical of thermal acclimation. CS, LDH and PK had relatively low thermal dependence over the 15-30°C range of assay temperatures (Q10=1.44-1.69).

View larger version (12K): [in a new window]   Fig. 5. A comparison of resting (N=5) and active (N=3) heart rates of juvenile green turtles during exposure to summer (filled bars) and winter (open bars) conditions. Heart rates during exposure to winter conditions were significantly lower than heart rates during the summer simulation (P<0.001). Active heart rates were significantly higher than resting heart rates during the summer and winter simulations (P=0.012).