The Role of Zinc Regulation in the Zinc Tolerance Mechanism of the Terrestrial Isopod Porcellio scaber

1. To elucidate mechanisms underlying adaptation to metals in the terrestrial isopod Porcellio scaber (Isopoda) responses to zinc were compared in field animals and laboratory-reared generations of three populations, one from a contaminated smelter site and the others from reference sites. 2. Isopods were exposed to a range of zinc concentrations in the food and their consumption, food and zinc assimilation, zinc concentration and internal zinc distribution were determined. 3. Isopods refused to eat food contaminated with 54 μ mol Zn g-1. 4. The zinc concentration of field isopods from the smelter site was three times higher than from the reference isopods. The mean fraction of zinc assimilated, determined as the difference between consumption and defecation (AEZn), was 25.3% for the reference isopods and 20.1% in the smelter isopods. When zinc assimilation was determined as the increase of the zinc body burden, the reference field isopods accumulated 3% of the zinc consumed; the increase in the smelter isopods was not significant. Isopods from both populations translocated zinc into the hepatopancreas. 5. In the laboratory-reared generations, food assimilation was reduced by zinc, this effect was more pronounced in the smelter isopods. In the smelter isopods, reduced food assimilation did not, however, result in less growth in comparison to the reference isopods. The AEZn did not differ significantly between the populations, but the increase in zinc body burden was again lower in the smelter isopods. 6. The higher growth efficiency of smelter isopods and their lower increase in zinc body burden may be regarded as an adaptation to zinc and may be one of the mechanisms contributing to survival of this population at a site severely polluted with zinc.