Hemolymph protein patterns and coprophagous behaviour inOniscus asellusL. (Crustacea, Isopoda)

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Abstract
The ingestion of an animal's own faeces (coprophagy) is a common phenomenon in terrestrial isopods. In the present investigation the influence of withholding faeces on growth and on the hemolymph protein composition of different life stages of the wood-louse Oniscus asellus was assessed. Juvenile Oniscus asellus reared without access to their faeces suffered severely under this treatment. Their gain in body mass was significantly lower than that in the control group. In contrast, the effect of non-coprophagous rearing was moderate or not detectable in subadult and adult individuals, respectively. No correlation occurred between coprophagy and survival rates in all test groups. The relative content of hemocyanin in the hemolymph of coprophagous as compared to non-coprophagous juveniles showed no significant differences. The same was true for the total protein content of the hemolymph in relation to the body mass. However, the relative amount of a distinct glycoprotein, which typically disappears under starvation, was clearly reduced in the non-coprophagous test groups. The benefits of the ingestion of faeces in terrestrial isopods may be related to the products of the coprophilous microflora. Withholding of these products leads to decreased growth rates and other deleterious effects. The deficiencies caused by the removal of the faeces are compensated for some time by using stored nutrients or by metabolizing of body tissue. Coprophagy may be looked upon as a multifactorial strategy, developed for an optimized use of nutrients by terrestrial isopods.