Preparatory adaptations for winter survival in the cold hardy beetles, Dendroides canadensis and Dendroides concolor

Thermal hysteresis (indicative of macromolecular antifreeze levels) was measured in hemolymph samples from the beetle, Dendroides canadensis, after acclimation to a short (8 h) photoperiod at 20 °C, or long (16 h) photoperiod at temperatures of 10 and 20 °C. Both the short photoperiod and low temperature (10 °C) treatment caused a significant elevation of thermal hysteresis, thereby implicating increased antifreeze protein production. Oxygen consumption rates of animals in each acclimation treatment were measured and no significant differences in metabolic rates were noted between treatments when measured at a high (20 °C) temperature. Thus, conditions which initiate antifreeze protein production fail to induce a diapause condition, characterized by a drop in metabolic rates. Likewise, natural populations sampled in mid-winter possess elevated levels of thermal hysteresis, and accumulated glycerol and sorbitol, but do not show a depressed metabolic rate. Therefore, D. canadensis do not enter a diapause during the winter, but are fully capable of achieving a high level of cold hardiness through the accumulation of antifreeze proteins and polyhydroxy alcohols. The possibility that Dendroides canadensis exhibited metabolic compensation under any acclimation treatment was examined and the results indicated that acclimation to a long photoperiod or low temperature did not affect oxygen consumption rates. In contrast, D. canadensis acclimated to a short photoperiod at 20 °C displayed considerable metabolic rate adjustments, as indicated by a Q₁₀ of 1.36. Dendroides concolor, a known congener of D. canadensis also displayed metabolic rate elevation at low temperatures following acclimation to a short photoperiod. For both species, the photoperiodically induced metabolic compensation was effected through a rotation in the metabolism-temperature curve. The results indicate that in the absence of a diapause, D. canadensis and D. concolor display metabolic rate compensation in response to seasonally changing photoperiods.