Temporal Plasticity in Cold Hardiness and Cryoprotectant Contents in Northern Versus Temperate Colias Butterflies (lepidoptera: Pieridae)

BACKGROUND: Butterflies Colias hyale and C. palaeno differ in distribution, habitat, voltinism and cold hardiness. OBJECTIVE: To compare changes in supercooling point (SCP) and cryoprotectant concentration(CPAc) of outdoor-reared caterpillars. MATERIALS AND METHODS: SCP was measured with a thermocouple and CPAc by gas chromatography monthly during winter. RESULTS: Seasonal changes in SCP and CPAc in overwintering larvae followed the pattern of change in ambient temperature. Only in warm November, SCP was low and CPAc high in boreal univoltine C. palaeno, whereas the opposite appeared in temperate multivoltine C. hyale. In mild December, SCP increased and CPAc decreased in C. palaeno, and acclimation reappeared in cold January. Both species differed in monthly cryoprotectant profiles, regarding both constitutive and inducible compounds. CONCLUSION: Seasonal pattern of SCP/CPAc enables C. palaeno to survive early frosts, but the costs of repeated acclimation during mild winters may set southern or low altitude limits of its distribution.