Freeze tolerance and freeze avoidance are typically described as mutually exclusive strategies for overwintering in animals.
Here we show an insect species that combines both strategies. Individual fungus gnats, collected in Fairbanks, Alaska, display
two freezing events when experimentally cooled and different rates of survival after each event (mean ± SEM: −31.5 ± 0.2°C,
70% survival and −50.7 ± 0.4°C, 0% survival). To determine which body compartments froze at each event, we dissected the abdomen
from the head/thorax and cooled each part separately. There was a significant difference between temperature levels of abdominal
freezing (−30.1 ± 1.1°C) and head/thorax freezing (−48.7 ± 1.3°C). We suggest that freezing is initially restricted to one
body compartment by regional dehydration in the head/thorax that prevents inoculative freezing between the freeze-tolerant
abdomen (71.0 ± 0.8% water) and the supercooled, freeze-sensitive head/thorax (46.6 ± 0.8% water).
Keywords Mycetophilidae -
Exechia nugatoria
- Supercooling - Exotherm
Communicated by H.V. Carey.