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First published online March 8, 2005
Journal of Experimental Biology 208, 869-879 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01455

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Deleterious effects of repeated cold exposure in a freeze-tolerant sub-Antarctic caterpillar

Brent J. Sinclair^* and Steven L. Chown

Spatial, Physiological and Conservation Ecology Group, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa

View larger version (22K): [in a new window]   Fig. 1. (A) Mass-independent critical thermal minimum (CTmin) onset and recovery (least-square means ± 95% confidence intervals) of P. marioni larvae repeatedly exposed to cold (filled squares, broken lines) or handling controls (open triangles, solid lines). Number of exposures on x axis includes 5 days recovery after final exposure (r-5). (B) Mass at dissection (g) and (C) gutless mass (g; mass at dissection – gut + contents) of Pringleophaga marioni larvae exposed to –5°C on up to 5 occasions (filled squares, broken line) and handling controls (open triangles and solid lines). Number of exposures on x axis, includes 5 days (r-5) and 30 days (r-30) recovery after 5 exposures. Values are least-square means with initial mass as covariate ± 95% confidence intervals. All analyses were performed as ANCOVA on log10-transformed data. Asterisks indicate masses that are significantly different from initial mass (0 exposures), on the basis of non-overlapping confidence intervals. Control-treatment pairs whose confidence intervals do not overlap are significantly different (P<0.05). Mass at dissection: main effect F1,134=80.99, P<0.0001; treatment x exposure interaction F7,134=4.721, P<0.0001. Gutless mass: main effect F1,133=21.61, P<0.0001; treatment x exposure interaction F7,133=1.71, P=0.112.

View larger version (26K): [in a new window]   Fig. 2. Body composition in Pringleophaga marioni larvae exposed to increasing numbers of freeze–thaw cycles (filled squares, dotted lines) or handling controls (open triangles, solid lines), and 5 (r-5) and 30 (r-30) days after the final exposure. Values are least-square means ± 95% confidence intervals of nine measurements. T indicates a significant difference between treatment and control, TxE indicates a significant treatment x exposure interaction. See Table S1 in supplementary material for statistics and covariates used for each analysis.

View larger version (12K): [in a new window]   Fig. 3. Frequency distribution of freezing events of Pringleophaga marioni larvae exposed five times to –5.5°C. Note that some caterpillars froze on every exposure, while others did not freeze at all; N=43. See Table S2 in supplementary material for individual freezing profiles.

View larger version (16K): [in a new window]   Fig. 4. (A) Proportion of caterpillars that froze at each exposure to –5.5°C. Filled squares, broken line: treatment animals, exposed to –5.5°C each time; N=43. Open triangles, solid line: handling controls, exposed to –5.5°C for the first time at each exposure; N=16. (B) Least-squares mean temperature of crystallisation (Tc) ± 95% confidence intervals (after ANCOVA with body mass as covariate) of control (open triangles, solid line) and treatment (filled squares, broken line) caterpillars exposed to repeated cold events. Only individuals that froze every time are included in the treatment data. Control animals were exposed to the same handling as the treatments, but each exposure was their first exposure to cold for those individuals.

View larger version (8K): [in a new window]   Fig. 5. Positive relationship between caterpillar mass (g) and the number of times an individual caterpillar froze during five exposures to –5.5°C. Pearson's correlation coefficient r=0.552, P<0.001, N=43.

View larger version (26K): [in a new window]   Fig. 6. Body composition of larvae of P. marioni exposed five times to –5.5°C, and that froze between 0 and 5 times during those exposures. Values are least-square means ± 95% confidence intervals of mass (g) measurements. Gut water differed significantly with frequency of freezing; significant differences are indicated by different letters above the bars. See Table S2 in supplementary material for statistics and covariates used in ANCOVA.

View larger version (33K): [in a new window]   Fig. 7. Hourly microclimate temperatures measured at 1 cm depth in soil at 200 and 800 m above sea level on the eastern side of Marion Island from the beginning of July to the end of October 2002.

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