Simultaneous freeze tolerance and avoidance in individual fungus gnats, Exechia nugatoria.
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 degrees C, 70% survival and -50.7 +/- 0.4 degrees 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 degrees C) and head/thorax freezing (-48.7 +/- 1.3 degrees 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).
Sformo
Todd
T
Institute of Arctic Biology, University of Alaska Fairbanks, PO Box 757000, Fairbanks, AK, 99775-7000, USA. rfts@uaf.edu
Kohl
F
F
McIntyre
J
J
Kerr
P
P
Duman
J G
JG
Barnes
B M
BM
D000005:Abdomen; D000413:Alaska; D000818:Animals; D001834:Body Water / Q000502:physiology*; D003080:Cold Temperature; D003681:Dehydration; D004175:Diptera / Q000502:physiology*; D005615:Freezing / Q000009:adverse effects*; D006813:Humidity; D007300:Insect Control; D012621:Seasons; D013312:Stress, Physiological / Q000502:physiology*; D015996:Survival Rate; D013909:Thorax; D044366:Transition Temperature; D014197:Trees