Does Porcellio scaber (Isopoda: Oniscidea) gain from coprophagy?

In feeding experiments, leaf litter of different tree species and isopod feces derived from these leaf litter materials were offered to the common woodlouse, Porcellio scaber. Consumption indices were used to elucidate the nutritional significance of coprophagy. Consumption rates of P. scaber clearly differed between feeding assays with alder (Alnus glutinosa) litter and those with isopod feces derived from alder. Differences between feeding assays depended on microbial activity of the food sources when oak (Quercus robur) litter or isopod feces derived from oak were offered. Further, microbiota increased the digestibility of oak material, but did not change digestibility of alder litter and reduced digestibility of feces derived from alder. Thus, the significance of litter- or feces-colonizing microbiota decreased with increasing nutritive value of the leaf litter. Inoculated feces derived from oak provided better growth than any other oak-derived food. In contrast, isopods grew better on alder litter than on alder-derived feces. In sum, we found little evidence to support the notion that P. scaber gains from coprophagy. We reject the hypothesis that coprophagy meets a need for nutrients that, due to digestive incapabilities, cannot be satisfied by feeding on leaf litter alone. The hypothesis that microbial colonizers render feces attractive as a source of microbial enzymes or nutrients is only partly corroborated. P. scaber gains from coprophagy through microbial activity or biomass only if leaf litter quality is low.