Martin Zimmer

Microorganisms and Cellulose Digestion in the Gut of the Woodlouse Porcellio scaber

In the common woodlouse Porcellio scaber different parts of the gut were observed with respect to microbial counts, cellulose activity, and degradation of cellulose. Cellulose is mainly digested in the anterior part of the hindgut, as was indicated by the distribution of cellulolytic activity and the decrease of cellulose content inside the gut. The cellulases woodlice utilize for the degradation of litter are mainly produced by endosymbiotic bacteria in the hepatopancreas rather than by microorganisms ingested with the food. Microorganisms ingested with the litter are digested in the anterior part of the hindgut and may provide an important food source. In the posterior hindgut, bacterial proliferation ensures microbial colonization of feces.

The role of coprophagy in nutrient release from feces of phytophagous insects

Abstract In microcosms containing soil from a mixed deciduous forest, we examined the nutrient release from feces of phytophagous insects through coprophagous behavior of saprophagous soil animals during 12 weeks of decomposition. The decomposition of feces of Operophthera fagata (Lepidoptera: Geometridae) fed on beech ( Fagus sylvatica ) released more cations (Ca 2+ , Mg 2+ , K + ) into the soil than the decomposition of beech litter, whether or not woodlice, Porcellio scaber and Oniscus asellus (Isopoda: Oniscidea), were present. Similarly, the C/N ratio of the soil was lower in assays with feces than in those with leaf litter. Coprophagy by isopods resulted in decreased C/N ratio of the soil. Respiratory activity of soil microbiota was greater when woodlice degraded Operophthera feces than when they degraded beech litter for 12 weeks. The present study provides evidence for nutrient release from the feces of phytophagous insects into the soil through the feeding activity of coprophagous soil animals.

Responses of the parthenogenetic isopod, Trichoniscus pusillus (Isopoda: Oniscidea), to changes in food quality

Summary Long-term observations of Trichoniscus pusillus revealed that chemical composition and microbial activity of the leaf litter serving as food influenced the reproductive success of females and the mortality rates of juveniles as well. Of the food sources investigated, only alder litter, exhibiting high microbial activity, allowed the maintenance of a stable population with frequently reproducing females. This study concludes that the food type is a significant factor for population parameters of this parthenogenetic isopod. Our results on T. pusillus, belonging to the taxon Synocheta, are compared with data on terrestrial isopod species of the taxon Crinocheta.

Surfactants in the gut fluids of Porcellio scaber (Isopoda: Oniscidea), and their interactions with phenolics.

Fluids from the gut lumen of Porcellio scaber showed significantly reduced surface tension compared to a buffer solution. Tests with several dilutions indicated that the concentration of the surface active substances (surfactants) was about 80-fold higher than the critical micelle concentration. Phenolics, e.g. gallotannins, when ingested in the diet increased the surface tension of the gut fluid, indicating reduced concentrations of free surfactants. The significance of gut surfactants in P. scaber, their role in digestive processes, and their interaction with tannins in this saprophagous soil arthropod are discussed.

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

Abstract 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.

Correspondence analytical evaluation of factors that influence soil macro-arthropod distribution in abandoned grassland

Summary We analysed field data on the occurrence of woodlice and millipedes in abandoned grassland in southwestern Germany using multivariate ordination statistics to extract information on single environmental factors influencing the distribution of particular species in the field. Different methods (DECORANA, CANOCO) revealed slightly different patterns of ordination, but led to similar conclusions. These conclusions coincide with previously observed ecophysiological requirements of isopods, and confirm the significance of the soil pH for their distribution. Howewer soil pH did not appear to be significant for diplopods. The distribution of diplopod species mainly corresponds with mean annual air temperature. Besides assigning particular species to single study sites that are characterised with respect to environmental factors, we statistically associate a group of three isopod species having similar ecological requirements.

Combined methods for the determination of microbial activity of leaf litter

Abstract A sensitive enzymatic test for glucose is introduced as a specific method for the determination of cellulolytic activity. The amount of released glucose serves as a measure for the cellulase activity of leaf litter, when crystalline cellulose is used as substrate. We compare the enzymatic measurement with an established method for the non-specific determination of glucose as a reducing carbohydrate. In comparison to our results on cellulase activity, the results of a modified determination of microbial respiration for small samples of leaf litter did not show the expected positive correlation to cellulolytic activities. This indication for differential effects of leaf litter characteristics on the composition of microbial populations provides arguments for suggesting simultaneous estimations of different measures for microbial activity.

NUTRITIONAL BIOLOGY OF TERRESTRIAL ISOPODS (ISOPODA: ONISCIDEA): COPPER REVISITED

ABSTRACT In Porcellio scaber, we detected extensive oxidation of phenolics by copper-containing enzymes in the hindgut. The activity of these phenol oxidases significantly correlated with the number of bacteria in the hepatopancreas. About one quarter of the hepatopancreatic copper was localized in these bacterial cells. We conclude that copper-containing phenol oxidases in the gut of P. scaber originate from the hepatopancreatic bacteria. Furthermore, our data provide evidence that microbial colonization and coprophagy, serving as an “external rumen, may be less important with respect to litter degradation by terrestrial isopods than has been previously assumed.