Balancing nutritional requirements for copper in the common woodlouse, Porcellio scaber (Isopoda: Oniscidea)

Abstract

We studied the copper budget, feeding preferences and digestive processes in the common woodlouse, Porcellio scaber, feeding on experimentally copper-contaminated leaf litter. Isopods lost copper from their body storage when feeding on a copper-free artificial diet for 4 weeks. The copper balance in subsequent feeding experiments depended on both the pre-experimental copper treatment and the copper content of leaf litter that has been experimentally increased to mimic a food source from a copper-contaminated area. Although the overall copper uptake did not depend on microbial activity, the copper content of isopod feces from feeding experiments provided evidence for increased copper absorption through leaf litter-colonizing microbiota. Consumption of leaf litter was influenced by the pre-experimental copper treatment of isopods and the copper content of the leaf litter. Food assimilation was affected by microbial leaf litter activity and both pre-experimental copper treatment of isopods and copper content of the leaf litter. Growth rates differed between food sources, but no effect of copper or microbial activity was evident. The duration of molt cycles was prolonged when feeding on copper-contaminated leaf litter, indicating long-term sub-lethal toxic effects of copper contamination, but both microbial activity of experimental leaf litter and pre-experimental acclimatization of isopods to moderate copper contamination reduced this effect. In feeding preference tests, both copper-fed and copper-deficient woodlice preferred copper-poor leaf litter over experimentally contaminated leaf litter with high copper content. The preference for copper-poor leaf litter was neither affected by the litter type nor by the activity of litter-colonizing microbiota, but appears to indicate the avoidance of copper-contaminated litter. Sensory preference tests provided evidence for direct detection of copper in leaf litter extracts through contact-chemoreception. Isopods turned significantly more often towards aqueous extracts of copper-poor leaf litter than of copper-contaminated leaf litter. Our data show that even copper-deficient isopods avoid excessive consumption of highly copper-contaminated leaf litter although copper increases its digestibility. Copper absorption is independent of the body copper content but is facilitated by leaf litter-colonizing microbiota. Further, microbiota as well as previous exposure to copper reduce the toxic effects of copper.