Water relations of the terrestrial isopodsPorcellio laevis andPorcellionides pruinosus (Crustacea, Oniscoidea)

Abstract

Some aspects of the water relations of the terrestrial isopodsPorcellio laevis andPorcellionides pruinosus were investigated using a technique which provides a continuous record of the water lost by the specimen to a moving air stream. Water loss in both species varied considerably with time and was characterized by numerous moisture peaks due in part to movement by the animals. In living isopods, the water loss rate ofP. laevis was significantly higher than that ofP. pruinosus; however, the water loss rates of dead isopods were considerably lower than those of living animals, and the interspecific differences were absent after death. It was concluded that some additional avenue of water loss was present in living animals, although blockage of the mouth and anus ofP. laevis had little effect on the water loss rate. Cuticular permeability, measured in dead isopods, increased in both species with increasing temperatures (25 to 50° C), with the most marked changes occurring between 40 and 50° C. The increase in water loss rate persisted even after correction for saturation deficit.