Overwintering Physiology Of Arctic And Subarctic Insects From Interior Alaska

Abstract

This dissertation focuses on the overwintering of three insects from Interior Alaska: a hemipteran, Elasmostethus interstinctus, and a coleopteran, Cucujus clavipes puniceus, that are freeze avoiding in the strict sense of the phrase, and a dipteran, Exechia nugatoria, that is simultaneously partially freeze avoiding and freeze tolerant. The variability within the freeze avoidance strategy itself is a key theme throughout this dissertation. Two significant contributions to comparative physiology are the confirmation of insect vitrification (glass formation) with its attendant extension of freeze avoidance and survival into a new, extreme low temperature record of -100�C and the simultaneous coupling of freeze avoidance and tolerance within an individual, which may more properly be described as a new overwintering strategy. Vitrification is the process by which ice crystallization is circumvented, resulting in a supercooled amorphous solid. Through a combination of antifreeze proteins that inhibit ice nucleation, dehydration tolerance, presence of high glycerol concentration, and low temperatures, the mobility of the remaining liquid water molecules is reduced, effectively by-passing the crystalline state. The second contribution is the discovery of a new overwintering strategy that combines freeze avoidance and freeze tolerance within an individual. In this case, the abdomen freezes (and the insect survives), while the contiguous head/thorax remains supercooled. These findings lead to the following evolutionary and trans-disciplinary questions. Is vitrification an adaptation? What is the selective advantage of compartmentalizing ice between body sections of an individual insect? Is this new overwintering strategy an example of a species transitioning between either becoming exclusively freeze avoiding or free tolerant? Applying new understanding of mechanisms of insect vitrification and avoidance of devitrification to cryomedicine may extend preservation of human tissues and organs. Similarly, for physical and material scientists, by understanding the patterns of ice formation within insects that tolerate, inhibit, and/or impede ice formation below the homogeneous ice nucleation temperature of water (-40�C), new biomimetic possibilities can be envisioned.