WATER FLUXES IN TERRESTRIAL ISOPODS

ABSTRACT

Exchanges of body water with the air were measured in a series of 16 species of terrestrial isopods from hygric to arid habitats using tritium as a tracer. Water fluxes were highest in the hygric, littoral species Alloniscus oahuensis and Deto marina. Species from arid and xeric habitats, Armadillo officinalis, Armadillidium fallax, Schizidium tiberianum from Mediterranean habitats, and Armadillidium vulgare from mesic habitats, had uniformly low water fluxes. Other mesic species had higher fluxes. The fractional exchange of body water was largely a function of the size of the body water pool. Flux data were used to predict threshold water activities for water vapor absorption. The similarity of the threshold values for arid, xeric, and certain mesic species suggests that the published value for Armadillidium vulgare is close to the minimum threshold for water vapor absorption likely to be found in terrestrial isopods. The rates of water exchange declined at ambient water activities below the threshold in most species.