Metabolic consequences of rapid cycles of temperature change for freeze-avoiding vs freeze-tolerant insects

Abstract

The metabolic responses to repeated cycles of temperature change, alternating 24 h at −16 and +3°C, were compared for a freeze-tolerant ( Eurosta solidaginis) vs a freeze-avoiding ( Epiblema scudderiana) insect. The two species differed most strongly in the response by cellular energetics. ATP content and energy charge were depressed in E. scudderiana larvae with each −16°C exposure but rebounded with each return to +3°C; after 12 such cycles, final energy status at +3°C was not significantly different than control values. By contrast, E. solidaginis larvae maintained a high energy charge (at the expense of a decrease in the total adenylate pool) over the first two cycles of freeze/thaw only. Subsequently energy stress was cumulative, with no recovery in the +3°C half of each cycle, and energy charge fell to 0.70–0.75. Both species showed a rise in glucose-6- P with each cold exposure, indicative of cold shock activation of glycogen phosphorylase. E. scudderiana showed no net increase in cryoprotectant content over the experimental course but sorbitol levels rose 4-fold in E. solidaginis. Alanine content increased significantly in E. solidaginis over the 12 cycles but no glycolytic end products accumulated in E. scudderiana. The data indicate that the freeze-avoiding specie is better able to maintain cellular homeostasis in the face of rapid and wide variations in environmental temperature than is the freeze-tolerant specie and that this may represent a worthwhile advantage of the freeze-avoidance strategy of cold hardiness for some species.