Changes in supercooling with body size, sex, and season in the long‐lived milliped Polyzonium germanicum (Diplopoda, Polyzonidae)

Abstract

The supercooling points (SCPs) of a field population of Polyzonium germanicum were measured at different stages in the life cycle. There was no post‐freezing survival under the experimental conditions used. The mean SCP was ‐26.2°C for eggs and increased to ‐18.2°C for juveniles of stadium III experiencing their first winter. From stadium V onwards, SCP varied considerably among individuals, ranging from ‐22.7 to ‐4.7°C. SCP was shown to increase significantly with body size in both sexes. Seasonal changes also occurred in males, SCP being lower in autumn‐winter than in spring‐summer. Measurements from a sample starved in the laboratory showed that the winter decrease could result from starvation affecting a proportion of males in the field. There was no relationship between the SCP and relative water content of individuals. After starvation in the laboratory, however, there was a relationship between the SCP and relative fat content of males. The results show that freezing is not a significant threat to the field population studied, with the possible exception of the largest overwintering females.