Water relations in millipedes from some alpine habitat types (Central Alps, Tyrol) (Diplopoda)

Five species of millipedes, living cither in a mixed oak wood (alt. 670 m) (Enantiulus nanus, Mastigona mutabilis) or in an Alnus viridis community (alt. 2000 m) ( Leptoiulus saltuvagus, Haasea fonticulorum and Ochogona caroli) and the nival species Trimerophorella nivicomes are compared in respect of their desiccation tolerance and their capacity to take up water from moist substrate. Results are expressed as the change of the initial water content of normally hydrated animals (Δm0, % h-1) and as the rate of transpiration per unit surface area per unit time per saturation deficit (µg cm-2 h-1 mmHg-1). At 0% r.h. and at 25° C, O. caroli (44.6% h-1), M. mutabilis (54.6) and H. fonticulorum (65.5) lost their water at rates higher than L. saltuvagus (9.1), T. nivicomes (9.8) and E. nanus (17.4). The tolerable water loss, expressed as a percentage of the initial body water, varied between 21 % (E. nanus) and 44.2% ( L. saltuvagus). The uptake of water by eversion of rectal tissue onto moist surface seems to be an important source of water gain. Dehydrated animals of M. mutabilis absorbed at a maximal rate of 79% h-1. The ecological implications of these facts are discussed.