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

Authors

  • J.-F. David,

    1. Laboratoire d'Ecologie générale (ER 71, C.N.R.S.), Museum national d'Histoire naturelle, 4 avenue du Petit-Chateau, F-91800, Brunoy, France
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    • *

      Centre d'Ecologie Fonctionnelle et Evolutive, C.N.R.S., 1919 Route de Mende, B.P. 5051, F-34033, Montpellier, Cedex 1, France

  • G. Vannier

    1. Laboratoire d'Ecologie générale (ER 71, C.N.R.S.), Museum national d'Histoire naturelle, 4 avenue du Petit-Chateau, F-91800, Brunoy, France
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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.

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