A small set of overwintering insects are termed freeze tolerant and can survive the anoxic and osmotic stresses associated with extracellular ice formation. A recent study indicated repeated freezing negatively impacts survival greater than a single freeze of the same cumulative duration. However, it is unclear if the reduced survival is due to repeated cellular osmotic stress and/or oxidative stress during oxygen reperfusion upon thawing. To determine if repeated anoxia and oxygen reperfusion may reduce survival, we measured oxidative protein damage (µmol chloromine T/µg protein), survival based on pupation, and percentage of fat body cell viability for cold tolerance of Eurosta solidaginis larvae subjected to either 0, 10, 20 or 30 cycles of diurnal anoxia/reperfusion. To standardize for time spent anoxic, we also tested a separate group of larvae that were exposed to a single bout of anoxia for 15 straight days. Although there was a trend of reduced aqueous antioxidants, there was no significant increase in oxidative protein damage compared to controls. Every group exposed to multiple repeated anoxic exposures had a significant increase in lipid peroxidation compared to controls with the highest values occurring at 24h and 168h post final exposure for animals subjected 20 exposures. Even though repeated anoxia subjected animals to oxidative stress, it had little effect on animal survival, as pupation percentages averaged 75.2% for all groups. Interestingly, repeated anoxia limited cold tolerance as animals subjected to repeated anoxia followed by an exposure to -80°C for five days had reduced fat body cell survival (61.3 ± 2.5%) compared to controls (69.3 ± 2.9%). In conclusion, repeated anoxia and oxygen reperfusion resulted in oxidative stress, especially with increased bouts of exposure, however it did not negatively affect organismal survival. Anoxia exposure did reduced cold tolerance and may work synergistically with other stressors associated with freezing to limit survival after repeated freezing and thawing in nature.
|Commitee:||Fowler, Thomas, Luesse, Darron|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 55/02M(E), Masters Abstracts International|
|Keywords:||Cryobiology, Eurosta solidaginis, Overwintering, Oxidative stress|
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