Molecular and biochemical adaptations in two cold-hardy gall insects.
Terrestrial insects have evolved molecular and biochemical adaptations that have allowed them to exploit virtually all climates on earth. Insects living in temperate and polar climates are forced to deal with freezing temperatures head-on. Two strategies of cold-tolerance in insects have emerged, freeze-tolerance and freeze-avoidance. Freeze-tolerantallow extracellular ice formation, whereas freeze-avoiding species depress the supercooling point of their body fluids below temperatures that they would normally encounter as part of their life-cycle. This research used a model species from each category of cold-tolerant insects. The model species chosen wereEpiblema scudderiana, a freeze-avoiding gall moth, and Eurosta solidaginis, a freeze-tolerant gall fly. Previous studies on these systems were based on measuring physiological parameters such as substrate utilization of product build-up. Results presented here are from molecular and biochemical studies completed to further our understanding of cold-tolerance and hypometabolism. Studies also included the effects of hypoxia on the two model species because this stress is often associated with freezing. The first step in each type of experiment was to examine how these species responded in nature and then see if we could reproduce that response under laboratory conditions to identify the trigger for such a response. The mechanism of ion pump regulation was examined and possible mediators of control were proposed. Three different gene expression analysis techniques were employed in an effort to identify key gene product that contribute to cold and hypoxic tolerance. Gene expression studies and enzyme assays have indicated that the role of the mitochondria in cold and hypoxic tolerance is more dynamic that previously understood. In addition, the MAP kinase superfamily of signal transduction has clearly been implicated in the survival success of these insects. The p38 family of MAPK is of particular interest because there were clear differences in this pathway between the freeze-tolerant and freeze-avoiding species. Reversible phosphorylation in undoubtedly a key mechanism of control in insect hypometabolism and stress tolerance. Finally, the role of NF-κB and the inflammatory response appears to be significant in the over winter survival of both species.