Effect of summer frost exposures on the cold tolerance strategy of a sub-Antarctic beetle

• Published in: Journal of Insect Physiology
• Main Authors: Bale, J.S., Worland, M.R., Block, W.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2001
• Subjects: Antarctic; Antarc*
• Online Access: http://nora.nerc.ac.uk/id/eprint/18366/; http://www.sciencedirect.com/science/article/pii/S002219100100097X

The sub-AntarcticbeetleHydromedion sparsutum (Coleoptera, Perimylopidae) is common locally on the island of South Georgia where sub-zero temperatures can be experienced in any month of the year. Larvae were known to be weakly freeze tolerant in summer with a mean supercooling point (SCP) around −4°C and a lower lethal temperature of −10°C (15 min exposure). This study investigated the effects of successive freezing exposures on the SCP and subsequent survival of summer acclimatised larvae. The mean SCP of field fresh larvae was −4.2±0.2°C with a range from −1.0 to −6.1°C. When larvae were cooled to −6.5°C on 10 occasions at intervals of 30 min and one and four days, survival was 44, 70 and 68%, respectively. The ‘end of experiment’ SCP of larvae surviving 10 exposures at −6.5°C showed distinct changes and patterns from the original field population depending on the interval between exposure. In the 30 min interval group, most larvae froze between −6 and −8°C, a depression of up to 6°C from the original sample; all larvae were dead when cooling was continued below the SCP to −12°C. In the one and four day interval groups, most larvae froze above −6°C, showing no change as a result of the 10 exposures at −6.5°C. As with the 30 min interval group, some larvae froze below −6°C, but with a wider range, and again, all were dead when cooled to −12°C. However, in the one and four day interval groups, some larvae remained unfrozen when cooled to −12°C, a depression of their individual SCP of at least 6°C, and were alive 24 h after cooling. In a further experiment, larvae were cooled to their individual SCP temperature at daily intervals on 10 occasions to ensure that every larva froze every day. Most larvae which showed a depression of their SCP of 2–4°C from their day one value became moribund or died after six or seven freezing events. Survival was highest in larvae with SCPs of −2 to −3°C on day one and which froze at this level on all 10 occasions. The results indicate that in larvae in which the SCP is lowered ...